PSYC 575 Cognitive Psychology

Article review. You can select any article pertaining to cognitive psychology, but I suggest that you select an article that you could use in your paper on false memories.  The article should be a peer reviewed journal article that discusses an experiment the authors actually conducted (i.e. a primary source).  In other words, the article cannot be a review article, meta-analysis, editorial or something from the popular press.  In all of these examples the author is discussing someone else’s work and you’re reading about it second-hand.

Overview

For each Journal Article Summary, you will choose an article to review and use the
Journal Article Summary Template to complete the assignment. The article you select must be a peer-reviewed journal article in the field of cognitive psychology. The article must also be a primary source, meaning that the authors are discussing their own research, not others’ research (e.g. review articles). Do not use an article that conducted a meta-analysis. It is ideal to select an article that you will be using in your paper; however, this is not a requirement. If you use an article that does not meet these criteria, you will not receive credit for this assignment. See the example below for detailed explanation of the required material for each question. Submit the completed form and a PDF of the article being reviewed. All material must be in current APA format.

Instructions

1. APA reference of article being reviewed

Write the reference for the article as if it were in the reference section of your paper.

2. What is the research problem that is being investigated? What is the purpose of the research being conducted?

Provide the “why” behind the paper. Why have they conducted this experiment? For example: “These experiments were designed to explore the role of second order conditioning in anxiety disorders.”

3. What is the research question?

The research question is more specific. What is the specific question or questions the article will answer as a result of the study or experiment? For example: “Are adolescents more sensitive to the memory imparting effects of alcohol?”

4. What are 2 or more theories that are discussed in the Introduction? How are they used to motivate (or set up) the research question? Do the authors agree or disagree with these theories?

Simply restate the theories discussed in the introduction in your own words. State how these theories are driving the research questions. If the authors’ hypothesis is correct, will it support the theory or be inconsistent with the theory? You should have good idea of where the authors stand based on the evidence presented and the arguments they are making.

5. How is the research question operationalized? First, identify the abstract constructs being studied. Next identify the concrete way these are being observed or measured. This should include your IV and DV.

A construct is an abstract explanatory variable that this not directly observable (e.g. memory). The concrete way the construct is measured will point you to the dependent variable (DV). For example, if the paper is concerned with memory, the DV may be the number of items recalled. The independent variable (IV) could be the amount of sleep each participant was allowed the night before the test. Remember that we cannot directly measure many of the constructs that are studied in psychology, so it is important that we identify how they are being operationalize in each research study.

6. What is the research design (i.e. between or within subjects, what type of statistical tests were used, what were the levels of each variable)?

This information will be in the methods section of your paper. Be sure to provide enough detail to describe how the study was designed.

7. Describe the results (but not their broader implications). Were the results significant? Which ones? Do these support or not support the hypothesis?

Describe the result in your own words. For example: Group X were able to recall significantly more words than Group Y. This finding supports the hypothesis that manipulation Y would reduce recall.

8. What limitations are mentioned? Why are these limitations theoretically interesting?

Limitations can be found in the discussion section of the paper. If a limitation is that they didn’t have X control group, then explain in your own words why that is important. Does it change the interpretation of the findings?

Note: Your assignment will be checked for originality via the Turnitin plagiarism tool.

Page 2 of 2

https://doi.org/10.1177/1745691619862306

Perspectives on Psychological Science
2019, Vol. 14(6) 1072 –109

5

© The Author(s) 2019

Article reuse guidelines:
sagepub.com/journals-permissions
DOI: 10.1177/1745691619862306
www.psychologicalscience.org/PPS

ASSOCIATION FOR
PSYCHOLOGICAL SCIENCE

The past is never dead. It’s not even past.

Faulkner (1950/2011, p. 73)

More than 20 years ago, Crews (1995) coined the term
“memory wars” to refer to a contentious debate regard-
ing the existence of repressed memories, which refers
to memories that become inaccessible for conscious
inspection because of an active process known as
repression. This debate raged throughout the 1990s and
was widely assumed to have subsided in the new mil-
lennium. A number of prominent authors who were
skeptical of repressed memories (e.g., Barden, 2016;
McHugh, 2003; Paris, 2012) declared the memory wars
to be effectively over, essentially arguing that most

researchers and clinicians now understand that believ-
ing in such memories without reservation is at best
questionable scientifically. The argument among these
authors is essentially that the recovered-memory skep-
tics won. Others argue that the memory wars have been
resolved in the opposite direction, stating that there is
now better evidence for a trauma-dissociation model
and less room for a skeptical stance toward repressed
(dissociated; see below) memories (Dalenberg et  al.,

862306 PPSXXX10.1177/1745691619862306Otgaar et al.Return of the Repressed
research-article2019

Corresponding Author:
Henry Otgaar, Faculty of Psychology and Neuroscience, Section
Forensic Psychology, Maastricht University, Universiteitssingel 40, 6200
MD, Maastricht, the Netherlands
E-mail: henry.otgaar@maastrichtuniversity.nl

The Return of the Repressed: The
Persistent and Problematic Claims
of Long-Forgotten Trauma

Henry Otgaar1,2,3 , Mark L. Howe1,2, Lawrence Patihis4 ,
Harald Merckelbach1, Steven Jay Lynn5, Scott O. Lilienfeld6,
and Elizabeth F. Loftus7

1Faculty of Psychology and Neuroscience, Section of Forensic Psychology, Maastricht University;
2Department of Psychology, City, University of London; 3Leuvens Institute of Criminology, Faculty
of Law, Catholic University of Leuven; 4School of Psychology, University of Southern Mississippi;
5Laboratory of Consciousness, Cognition, and Psychopathology, Binghamton University; 6Department of
Psychology, Emory University; and 7Department of Psychological Science, University of California, Irvine

Abstract
Can purely psychological trauma lead to a complete blockage of autobiographical memories? This long-standing
question about the existence of repressed memories has been at the heart of one of the most heated debates in modern
psychology. These so-called memory wars originated in the 1990s, and many scholars have assumed that they are over.
We demonstrate that this assumption is incorrect and that the controversial issue of repressed memories is alive and
well and may even be on the rise. We review converging research and data from legal cases indicating that the topic
of repressed memories remains active in clinical, legal, and academic settings. We show that the belief in repressed
memories occurs on a nontrivial scale (58%) and appears to have increased among clinical psychologists since the
1990s. We also demonstrate that the scientifically controversial concept of dissociative amnesia, which we argue is a
substitute term for memory repression, has gained in popularity. Finally, we review work on the adverse side effects
of certain psychotherapeutic techniques, some of which may be linked to the recovery of repressed memories. The
memory wars have not vanished. They have continued to endure and contribute to potentially damaging consequences
in clinical, legal, and academic contexts.

Keywords
memory wars, repressed memory, repression, false memory, recovered memory, therapy

http://www.psychologicalscience.org/pps

mailto:henry.otgaar@maastrichtuniversity.nl

https://sagepub.com/journals-permissions

http://crossmark.crossref.org/dialog/?doi=10.1177%2F1745691619862306&domain=pdf&date_stamp=2019-10-04

Return of the Repressed 1073

2012). Some proponents of the idea of dissociative
amnesia (i.e., the inability to remember autobiographic
experiences usually as a result of trauma) have even
likened skeptics to climate-science deniers (Brand et al.,
2018, in response to Merckelbach & Patihis, 2018). Their
argument appears to be that they have won the memory
wars, and further proof of this is the continued inclusion
of dissociative amnesia in the fifth edition of the Diag-
nostic and Statistical Manual of Mental Disorders (DSM–
5; American Psychiatric Association, 2013; see also
Spiegel et al., 2011).

In this article, we present evidence that the debate
concerning repressed memories is by no means dead.
To the contrary, we contend that it rages on today and
that the term dissociative amnesia is being used as a
substitute term for repressed memory. To buttress this
point, we present converging lines of evidence from
several sources suggesting that the concept of repressed
memories has not vanished and that it has merely reap-
peared in numerous guises (e.g., in the context of dis-
sociative amnesia). Admittedly, some researchers have
argued that the memory wars have persisted (e.g.,
Patihis, Ho, Tingen, Lilienfeld, & Loftus, 2014), but no
review has systematically and critically evaluated this
proposition. In this article, we amass evidence from
multiple sources showing that beliefs associated with
repressed memories and related topics such as dissocia-
tive amnesia, far from being extinguished, as claimed
by some scholars, remain very much alive today. Fur-
thermore, we demonstrate that these beliefs carry sig-
nificant risks in clinical and legal settings.

Repressed Memories and the
Memory Wars

As Ellenberger (1970) explained in his classic mono-
graph, the concept of repressed memories traces its
roots to the psychoanalytic theory and practice of Sig-
mund Freud, who in turn was influenced by physician-
hypnotists, such as Jean-Martin Charcot, in the final
decades of the 19th century. At the heart of this concept
is the idea that traumatic experiences are often so over-
whelming that people use defense mechanisms to cope
with them. One of these mechanisms involves the auto-
matic and unconscious repression of the traumatic
memory with the consequence that people no longer
recollect or retain awareness of the experience that
triggered it (e.g., Loftus, 1993; McNally, 2005; Piper,
Lillevik, & Kritzer, 2008). Nevertheless, according to this
view, the repressed trauma ostensibly exacts a serious
mental and physical toll (Hornstein, 1992), manifesting
itself psychologically and somatically in a wide array
of symptoms (e.g., fainting, amnesia, mutism). This
influential body-keeps-the-score hypothesis implies that

trauma can be “entirely organized on an implicit or per-
ceptual level, without an accompanying narrative about
what happened” (van der Kolk & Fisler, 1995, p. 512).
The goal of therapy is thus to make the implicit—the
repressed—explicit (Yapko, 1994a), following Freud’s
famous tenet that psychoanalysis aims to make the
unconscious conscious. Thus, the notion of repressed
memories encompasses three ideas: People repress trau-
matic experiences, the repressed content has psycho-
pathological potential, and recovering traumatic content
is necessary for engendering symptom relief.

In the 1990s, as we demonstrate in a review of data
of surveyed clinicians, the belief in repressed memories
was endemic in therapeutic circles. Even when patients
did not recollect the trauma, such as sexual abuse, some
therapists suggested that their unconscious may harbor
repressed memories. When clients presented with
symptoms of, for example, anxiety, mood, personality,
or eating disorders, many clinicians seemed to take
these symptoms as signs of long-repressed memories
of abuse. Furthermore, in the 1990s, dream interpreta-
tion, hypnosis, guided imagery, repeated cuing of mem-
ories, and diary methods, among other recovered-memory
techniques, were used by many practitioners to osten-
sibly uncover repressed memories and bring them to
the surface of consciousness. As a result of these treat-
ments, patients started to recover purported memories
of abuse, typically sexual abuse, and some filed crimi-
nal or civil suits against their alleged perpetrator (Loftus,
1994; Loftus & Ketcham, 1994).

During these therapeutic interventions, suggestive
techniques were commonly used to recover the alleged
repressed memory. At that time, laboratory research
began to show the deleterious effects of suggestion on
autobiographical recollections of childhood episodes.
In one of the first such studies, Loftus and Pickrell
(1995) asked students to report on four events that
happened in their childhood. One event was fabricated
and involved being lost in a shopping mall at about
5 years old. Students were told that their parents pro-
vided these narratives to the experimenters, while in
fact, parents had confirmed that the event did not hap-
pen. After three suggestive interviews, 25% (n = 6) of
the participants claimed that the false event in fact had
occurred. This and other studies during the 1990s indi-
cated that false autobiographical memories1 can be
implanted with suggestive interviewing techniques
(e.g., Hyman, Husband, & Billings, 1995; for earlier
relevant work, see Laurence & Perry, 1983; for a review
of false memories before 1980, see Patihis & Younes
Burton, 2015).

Many memory scholars have argued on the basis of
this research that repressed memories recovered in
therapy may not be based on true events but could be

1074 Otgaar et al.

false memories (Lindsay & Read, 1995; Loftus & Davis,
2006). An additional scenario offered by researchers is
that some people may reinterpret childhood events as
a result of therapy and come to experience this rein-
terpretation as a recovered memory of abuse (McNally,
2012). For example, Schooler (2001) argued that indi-
viduals may initially not experience their abuse as trau-
matic but later come to reevaluate it in this fashion.
This change in meta-awareness may be experienced as
a recovery of a memory when it instead comprises a
new interpretation of a memory that was accessible all
along. Schooler offered several case descriptions sug-
gestive of this intriguing process, but strictly speaking
it does not involve the reemergence of repressed mem-
ories into consciousness. Nevertheless, the reinterpreta-
tion account may be a plausible explanation of certain
recovered memories of events that were genuinely
experienced.

Still, not all cases that were described by Schooler
(2001) can be interpreted in terms of reevaluation.
Wagenaar and Crombag (2005), for example, noted the
inherent problems that such descriptions have to dem-
onstrate the existence of recovered memories. They
criticized Schooler’s case descriptions on the grounds
that many assumptions needed to be met to confirm
the existence of recovered memories in these cases. For
example, Wagenaar and Crombag observed that alleged
victims sometimes received therapy that may have influ-
enced their memories. In addition, Wagenaar and Crom-
bag noted that claiming to have forgotten sexual abuse
is not the same as having forgotten the abuse.

Apart from suggestive techniques that might lead to
the creation of memory aberrations, some memory
researchers noted that the concept of repressed memo-
ries is difficult to reconcile with studies on the effects
of trauma on memory. Specifically, a large body of data
suggests that the central aspects of trauma tend to be
relatively well remembered (McNally, 2005). Several
authors concluded that complete memory loss for trau-
matic events is rare among trauma victims, such as
Holocaust survivors (Wagenaar & Groeneweg, 1990),
survivors of Japanese/Indonesian concentration camps
(Merckelbach, Dekkers, Wessel, & Roefs, 2003), and
victims of sexual abuse (Goodman et al., 2003). Fur-
thermore, the idea of repressed memories runs counter
to well-established principles of human memory. For
example, purported repressed memories are often
about repeated experiences of abuse, but repeated
events are generally well recollected. In addition, peo-
ple with posttraumatic stress disorder (PTSD) frequently
experience flashbacks and intrusive memories of the
trauma and hence do not typically report repressed
memories, at least of their triggering traumatic event.
In addition, the idea of apparent recovered memories

suggests that experiences can be forgotten and “recov-
ered” following retrieval cues. This common memory
phenomenon does not require the idea of repressed
memories (for an overview, see Roediger & Bergman,
1998).

The recovery of mundane childhood memories is a
perfectly normal phenomenon, although people may
find it difficult to estimate how long they have not
thought about a childhood experience (Parks, 1999).
The recovery of a purportedly long-forgotten trauma is
less plausible in light of everything that we know about
traumatic memories (see above), and in such cases the
question is whether there is independent evidence to
corroborate the memory. Thus, a central issue concern-
ing recovered memories is whether they can be inde-
pendently corroborated. Studies examining corroborative
evidence of recovered memories are often limited
because they rely exclusively on victims’ characteriza-
tions of corroboration (e.g., Chu, Frey, Ganzel, &
Matthews, 1999; Herman & Harvey, 1997). Research in
which at least partial independent corroboration has
been sought demonstrated that continuous memories
of child sexual abuse recalled outside of therapy were
more often corroborated than discontinued memories
of abuse recovered in therapy (Geraerts et  al., 2007;
see also McNally, Perlman, Ristuccia, & Clancy, 2006).
Another key point concerning recovered memories is
that people may not think about the abuse for many
years or may forget their previous recollections of their
traumatic experience. Such people might then sponta-
neously recover memories of abuse when reminded
about the abuse outside of therapy. However, such a
phenomenon, psychologically important as it is, is a far
cry from repressing a richly detailed memory in its
entirety and later recalling it in therapy or everyday life
(McNally & Geraerts, 2009).

One way to examine how clinicians think about the
reality of repressed memories is to survey them about their
beliefs on the topic and on their technical knowledge of
how memory works. In this respect, a summary of
practitioner-survey studies since the 1990s is informative.

Memory Beliefs About Repressed
Memories: From Then to Now

Beliefs among clinical psychologists

Scientific interest in what therapists and other mental-
health professionals know about the functioning of
memory originated because incorrect beliefs about
memory could catalyze suggestive clinical practices and
flawed treatment plans (Gore-Felton et al., 2000). Yapko
(1994a, 1994b) conducted one of the first surveys of
memory beliefs of psychology professionals. He found

Return of the Repressed 1075

that 34% (n = 190) of master’s-level psychotherapists
and 23% (n = 48) of PhD psychotherapists agreed that
traumatic memories uncovered via hypnosis are authen-
tic. Moreover, 59% (n = 513) of clinicians agreed that
“events that we know occurred but can’t remember are
repressed memories” (Yapko, 1994a, p. 231). Yapko
(1994a) also found that 49% (n = 419) agreed that “mem-
ory is a reliable mechanism when the self-defensive
need for repression is lifted” (p. 232). Dammeyer,
Nightingale, and McCoy (1997) found that 58% (n = 64)
of PhD-level clinicians, 71% (n = 74) of PsyD-level clini-
cians, and 60% (n = 43) of MSW-level clinicians agreed
that repressed memories are genuine. Merckelbach and
Wessel (1998) detected an even higher percentage: 96%
(n = 25) of licensed psychotherapists endorsed the view
that repressed memories exist. Poole, Lindsay, Memon,
and Bull (1995; Survey 2) found that 71% (n = 37) of
clinical psychologists reported that they had encoun-
tered at least one case of a recovered memory (see also
Polusny & Follette, 1996).

These studies were performed in the 1990s, which
is considered to be the zenith of interest in repressed
memories. After that period, a wealth of research pub-
lished in psychological, psychiatric, and more legally
oriented journals concluded that the notion of repressed
memories is a highly problematic concept, particularly
in the courts (Loftus, 2003; McNally, 2005; Piper et al.,
2008; Porter, Campbell, Birt, & Woodworth, 2003; Rofé,
2008; Takarangi, Polaschek, Hignett, & Garry, 2008).
Despite these critical articles, many psychologists, espe-
cially clinical and counseling psychologists, continue
to harbor the idea that traumatic memories can be bur-
ied for years or decades in the unconscious and later
recovered. Magnussen and Melinder (2012) surveyed
licensed psychologists and found that 63% (n = 540)
believed recovered memories to be “real.” Kemp,
Spilling, Hughes, and de Pauw (2013) demonstrated
that 89% (n = 333) of surveyed clinical psychologists
believed that memories for childhood trauma (such as
sexual abuse) can be “blocked out” for many years.
Patihis et al. (2014) found that 60.3% (n = 35) of clinical
practitioners and 69.1% (n = 56) of psychoanalysts
agreed that traumatic memories are often repressed.
Kagee and Breet (2015) found that 75.7% (n = 78) of
103 South African psychologists responded probably
or definitely true to the statement that “individuals com-
monly repress the memories of traumatic experiences”
(Kagee & Breet, 2015, p. 5).

Ost, Easton, Hope, French, and Wright (2017) showed
that 69.6% (n = 87) of clinical psychologists strongly
endorsed the belief that “the mind is capable of uncon-
sciously ‘blocking out’ memories of traumatic events”
(p. 60). Wessel (2018) recently examined memory
beliefs among eye-movement desensitization and repro-
cessing (EMDR) practitioners. EMDR is thought to be

effective in making traumatic memories less vivid and
emotionally negative (Lee & Cuijpers, 2013). Wessel
asked EMDR practitioners whether access to traumatic
memories can be blocked and found that 93% (n = 457)
responded affirmatively.

Beliefs among other professionals

Researchers have surveyed other professionals for
whom it would be important to possess accurate knowl-
edge concerning memory. Many of these studies did
not specifically ask about professionals’ beliefs con-
cerning the existence of repressed memories but instead
asked about issues related to eyewitness memory (e.g.,
confidence-accuracy relationship; see Magnussen,
Melinder, Stridbeck, & Raja, 2010). Exceptions to this
trend include the study by Benton, Ross, Bradshaw,
Thomas, and Bradshaw (2006). In an American sample,
they demonstrated that 73% (n = 81) of jurors, 50%
(n = 21) of judges, and 65% (n = 34) of law-enforcement
personnel believed in long-term repressed memories.
Odinot, Boon, and Wolters (2015) asked Dutch police
interviewers about whether traumatic memories can be
repressed. They found that 75.7% (n = 108) agreed that
they could. In a recent study, 84% (n = 133) of Dutch
child-protection workers indicated that traumatic mem-
ories are often repressed (Erens, Otgaar, Patihis, & De
Ruiter, 2019).

Beliefs among laypersons

Laypeople such as undergraduates have also been asked
in a number of studies to indicate their levels of belief
concerning the existence of repressed memories (Lynn,
Evans, Laurence, & Lilienfeld, 2015). Golding, Sanchez,
and Sego (1996) reported that (a) 89% of 613 under-
graduates were familiar with a circumstance in which
someone recovered a repressed memory, (b) 75% of
these students noted that the source of this information
was television, and (c) belief in repressed memories was
positively correlated with the amount of media expo-
sure. Merckelbach and Wessel (1998) found that 94%
(n = 47) of students endorsed the idea that repressed
memories exist. Magnussen et al. (2006) surveyed 2000
Norwegian people from the general public. They found
that 45% (n = 900) of respondents believed that trau-
matic memories can be repressed. Strikingly, 40% (n =
800) believed that people who committed a murder can
repress the memory of that event. Finally, Patihis et al.
(2014) found that 81% (n = 316) of undergraduates
believed that traumatic memories are often repressed.

On the basis of these survey data, we calculated the
overall percentage of people who believe in the exis-
tence of repressed memories in the combined samples
(see Table 1). Although caution needs to be exercised

1076 Otgaar et al.

Table 1. Percentages of People Who Believe in the Concept of Repressed Memory Among Various Studi

es

Study N % Statement Scale Country

Clinical psychologists
Yapko (1994a) 869 59 “Events that we know

occurred but can’t
remember are repressed
memories.”

Agree–disagree

U.S.

Dammeyer,
Nightingale, and
McCoy (1997)

111 58a “Do you believe that repressed
memory exists?”

1 = definitely no, 10 =
definitely yes

U.S.

Dammeyer et al.
(1997)

105 71 “Do you believe that repressed
memory exists?”

1 = definitely no, 10 =
definitely yes

U.S.

Dammeyer et al.
(1997)

75 60 “Do you believe that repressed
memory exists?”

1 = definitely no, 10 =
definitely yes

U.S.

Merckelbach and
Wessel (1998)

27 96 “[Does] repression exist?” Yes, no, don’t know

The Netherlands

Magnussen and
Melinder (2012)

858 63 “Sometimes adults in
psychotherapy remember
traumatic events from early
childhood, about which they
previously had absolutely
no recollection. Do you
think such memories are
real or false?”

All are real, most are
real, most are false,
all are false-uncertain

Norway

Kemp et al. (2013) 375 89 “Can memories for childhood
trauma (i.e., sexual abuse)
be ‘blocked out’ from
conscious memory for many
years?”

Yes, but rare; don’t
know; no, don’t
believe this

England and
Wales

Patihis et al. (2014) 58 60.3b “Traumatic memories are often
repressed.”

Strongly disagree,
disagree, slightly
disagree, slightly
agree, agree, strongly
agree

U.S.

Patihis et al. (2014) 82 69.1 “Traumatic memories are often
repressed.”

Strongly disagree,
disagree, slightly
disagree, slightly
agree, agree, strongly
agree

U.S.

Kagee and Breet
(2015)

103 75.7 “Individuals commonly repress
the memories of traumatic
experiences.”

Definitely untrue,
probably untrue,
probably true,
definitely true

South Africa

Ost et al. (2017) 125 69.6 “The mind is capable of
unconsciously ‘blocking
out’ memories of traumatic
events.”

1 = strongly disagree;
4 = strongly agree

U.K.

Wessel (2018) 492 93 “It is possible that access
to trauma memory is
blocked.”c

Agree, disagree, no
opinion

The Netherlands

Other professionals
Benton Ross,

Bradshaw,
Thomas, and
Bradshaw (2006)

111 73 “Traumatic experiences can
be repressed for many years
for many years and then
recovered.”

Generally true, generally
false, I don’t know

U.S.

(continued)

Return of the Repressed 1077

Study N % Statement Scale Country

Benton et al.
(2006)

42 50 “Traumatic experiences can
be repressed for many years
and then recovered.”

Generally true, generally
false, I don’t know

U.S.

Benton et al.
(2006)

52 65 “Traumatic experiences can
be repressed for many years
and then recovered.”

Generally true, generally
false, I don’t know

U.S.

Odinot, Boon, and
Wolters (2015)

143 75.7 “Traumatic experiences can
be repressed for many years
and then recovered.”d

Agree, disagree The Netherlands

Erens Otgaar,
Patihis, and De
Ruiter (2019)

158 84 “Traumatic memories are often
repressed because of their
painful content.”

Agree, disagree The Netherlands

Laypersons
Merckelbach and

Wessel (1998)
50 94 “[Does] repression exist?” Yes, no, don’t know The Netherlands

Magnussen et al.
(2006)

2,000 45 “Sometimes adults in
psychotherapy remember
traumatic events from early
childhood, about which they
previously had absolutely
no recollection. Do you
think such memories are
real or false?”

All are real, most are
real, most are false,
all are false-uncertain

Norway

Magnussen et al.
(2006)

2,000 40 “Sometimes adults in
psychotherapy remember
traumatic events from early
childhood, about which they
previously had absolutely
no recollection. Do you
think such memories are
real or false?”

All are real, most are
real, most are false,
all are false-uncertain

Norway

Patihis et al. (2014) 390 81 “Traumatic memories are often
repressed.”

Strongly disagree,
disagree, slightly
disagree, slightly
agree, agree, strongly
agree

U.S.

Note: U.S. = United States; U.K. = United Kingdom.
aRefers to people scoring 8, 9, or 10. bRefers to people who chose slightly agree, agree, or strongly agree. cTranslated from the Dutch: “goed
mogelijk dat toegang tot traumaherinnering is geblokkeerd.” dTranslated from the Dutch: “Traumatische ervaringen kunnen jarenlang worden
verdrongen (d.w.z. geheel vergeten zijn) en dan toch nog worden hervonden.

Table 1. (Continued)

when collapsing data across such surveys because the
samples may vary on many dimensions, aggregated
data can be informative given they can generally be
expected to cancel out largely random differences in
participant characteristics. On average, 58% (n = 4,745)
of those who were surveyed indicated some degree of
belief in the existence of repressed memories. When
we examined the prevalence of these beliefs across
subgroups within the combined sample, interesting
results emerged. Among clinical psychologists, 70%
(n = 2,305) believed in the existence of repressed mem-
ories. This percentage was somewhat lower in the 1990s

(61%; n = 719) and increased to 76% (n = 1,586) from
2010 onward. Furthermore, 75% (n = 377) of other
professionals expressed a strong belief in repressed
memories, as did 46% (n = 2,063) of laypersons.

We also performed additional analyses. For example,
when we focused only on survey items using the word
“repression,” we found a prevalence of 65% (n = 1,265)
in the belief of repressed memories. In addition,
because the items used differed to some extent among
survey studies, we concentrated on statements for
which people were asked specifically about the fre-
quency of repressed memories (e.g., “Traumatic

1078 Otgaar et al.

memories are often repressed”). When we focused on
these statements (Erens et  al., 2019; Kagee & Breet,
2015; Patihis et al., 2014), we found that 78% (n = 618)
of surveyed people believed that traumatic experiences
are often repressed. We also compared the rates of
belief in repressed memories in the 1990s with those
of all studies performed after the 1990s. A prevalence
of 62% (n = 766) was observed for studies in the 1990s;
this rate was slightly lower for studies performed after
the 1990s (57%; n = 3,979).

Taken together, our data suggest, perhaps surpris-
ingly, that mental-health professionals in our combined
samples were not more critical about repressed memo-
ries than were laypeople. This finding underscores our
argument that a belief in repressed memories is deeply
rooted in modern Western societies. Moreover, the data
suggest that despite a plethora of scientific work calling
the existence of repressed memories into question (e.g.,
Loftus & Davis, 2006), clinical psychologists’, other
mental-health professionals’, and the general public’s
views on repressed memories remain strong. Further-
more, it seems that belief in repressed memories even
increased within clinical psychologists.

Still, in certain groups of professionals, notably those
working in legal psychology, skepticism regarding
repressed memories is high. For example, Kassin, Tubb,
Hosch, and Memon (2001) found that 22% of experts
opined that repressed memories are “reliable enough”
to present as evidence in the courtroom. Likewise, some
recent research suggests that memory scientists tend to
harbor strong reservations concerning the existence of
repressed memories (only 12.5% agreed that repressed
memories can be retrieved in therapy accurately; 27.2%
of experimental psychologists agreed to some extent that
traumatic memories are often repressed; Patihis, Ho,
Loftus, & Herrera, 2018). It is important to emphasize
that many informed scientists are skeptical: It counters
the argument that repressed memories must exist because
so many people believe in them, a tempting logical error
termed the bandwagon fallacy (Briggs, 2014).

Many of these surveys relied on the terms repression
or repressed memories. These terms may have all kinds
of connotations, leading to artificially raised endorse-
ment patterns suggestive of belief in repressed memo-
ries. Brewin, Li, Ntarantana, Unsworth, and McNeilis
(2019; Study 3) recently argued that high endorsement
rates in the belief in repressed memories (to the state-
ment “Traumatic experiences can be repressed for many
years and then recovered”) actually reflect a belief in
conscious memory suppression (see section below on
retrieval inhibition). They found that when members of
the general public were asked about their belief in
conscious repression and were questioned regarding

repressed memories (“Traumatic experiences can be
repressed for many years and then recovered”), similar
endorsement rates were found. However, because
Brewin and colleagues did not include a survey item
on unconscious repression, it is unknown which
endorsement rates would be detected for such a con-
troversial statement. To remedy this omission, Otgaar
et al. (2019) specifically inquired about people’s belief
in unconscious repression. They found high endorse-
ment rates for belief in both conscious and unconscious
repression (around 60%), implying that the belief in
repressed memories is still widespread. In what follows,
we show that, as is true for the belief in repressed
memories, dissociative amnesia, a conceptual twin of
repression, has been deeply embedded into psychology
lore in such a way that it could be the most potent
threat to extending the memory wars.

Dissociative Amnesia = Repressed
Memories?

Despite the widespread belief in repressed memory,
the term “repression” became controversial in the mem-
ory wars and is now seldom used in a credible context
in scientific publications. After the concept became
intensely controversial, many clinicians adopted a new
and perhaps more palatable term dissociative amnesia.
This term became the preferred and more widely used
appellation for the process whereby traumas are ren-
dered inaccessible. For example, dissociative amnesia
is mentioned in DSM–5 (American Psychiatric Associa-
tion, 2013), whereas repressed memory or repression is
not.

There might be several reasons for why dissociative
amnesia is listed in the DSM–5. One likely reason is
that the substantial majority of the Task Force members
of the DSM–5 were psychiatrists rather than psycholo-
gists, and the Task Force did not include memory
experts (see Yan, 2007). This Task Force also did not
adequately reflect the full range of scientific opinions
regarding the empirical status of dissociative disorders,
including dissociative amnesia. Indeed, as Lilienfeld,
Watts, and Smith (2012) noted the following:

It is troubling that the DSM–5 Anxiety, Obsessive-
Compulsive Spectrum, Posttraumatic, and Dissociative
Disorders Work Group contains no members who
have expressed doubts in scholarly outlets regarding
the etiology of dissociative identity disorder and
related dissociative disorders (e.g., dissociative
amnesia, dissociative fugue), despite the fact that
these disorders are exceedingly controversial in the
scientific community. (p. 831)

Return of the Repressed 1079

Case studies of patients claiming dissociative amne-
sia have also figured prominently in the clinical litera-
ture, in turn perhaps contributing to the prima facie
validity of the construct of dissociative amnesia (e.g.,
Staniloiu, Markowitsch, & Kordon, 2018).

We propose that during and after the 1990s, when
the term repressed memory was widely criticized, pro-
ponents began to favor the term dissociative amnesia
instead. Perhaps Holmes (1994) was one of the first to
notice this trend:

In the absence of good laboratory or clinical
evidence for repression, proponents of the
concept have begun to emphasize dissociation
instead. But that is simply another name for
repression; if one dissociates oneself from an
event (is no longer aware of it), one has repressed
it. Dissociative amnesia is supposed to occur after
certain traumatic experiences. Yet  alleged cases
of this phenomenon are very rare. (p. 18)

Consistent with this idea, dissociative amnesia was not
mentioned in pre-1990s work on repression by Holmes
(1972, 1974) and Holmes and Schallow (1969). This
subtle but significant name change has muddied the
waters and provided a cover for the continued practice
of psychotherapy that involves repressed memories,
albeit under new terminology.

Dissociative amnesia is defined in the DSM–5 as the
“inability to recall autobiographical information” that
(a) is “usually of a traumatic or stressful nature,” (b) is
“inconsistent with ordinary forgetting,” (c) should be
“successfully stored,” (d) involves a period of time
when there is an “inability to recall,” (e) is not caused
by “a substance” or “neurological . . . condition,” and
(f) is “always potentially reversible because the memory
has been successfully stored” (American Psychiatric
Association, 2013, p. 298). These defining features serve
as an umbrella set of criteria for three types of dissocia-
tive amnesia listed in the DSM–5. Localized dissociative
amnesia applies to memory loss for a “circumscribed
period of time” and may be broader than amnesia for
a single traumatic event, for example, “months or years
associated with child abuse” (p. 298). Because localized
dissociative amnesia most resembles what was formerly
called repressed memory, it is noteworthy that the
DSM–5 calls this type “the most common form of dis-
sociative amnesia.” In selective dissociative amnesia, the
individual “can recall some, but not all, of the events
during a circumscribed period of time” (p. 298). Gen-
eralized dissociative amnesia involves “a complete loss
of memory for one’s life history” and “is rare” (p. 298).
The DSM–5 indicates “histories of trauma, child abuse,
and victimization” as features that support a diagnosis
of dissociative amnesia (p. 299).

Although dissociative symptoms can manifest them-
selves in contexts quite different from trauma—for exam-
ple, after the ingestion or administration of the anesthetic
ketamine (Simeon, 2004) or ecstasy, cannabis, and
cocaine (van Heugten-van der Kloet et al., 2015)—Table
2 illustrates similarities in the definitions of dissociative
amnesia from the DSM–5 and definitions advanced by
scientific skeptics of repressed memory (text from Loftus,
1993; and Holmes, 1974). We contend, on the basis of
striking parallels in definitions, that skeptical arguments
against repressed memories should apply with equal
force to dissociative amnesia. More specifically, defini-
tions of both dissociative amnesia and repressed memory
share the idea that traumatic or upsetting material is
stored, becomes inaccessible because of the trauma, and
can later be retrieved in intact form.

Although repressed memory as a concept is rarely
defended in scientific circles these days, the idea of
dissociative amnesia has become popular, especially in
some psychiatric quarters. For example, between 2010
and 2019, the Journal of Trauma & Dissociation has
published 71 articles related to dissociative amnesia;
between 1990 and 1999, no such articles were pub-
lished.2 This ascension appears to be a major reason
for the revitalization of the memory wars and for the
continuation of therapies that attempt to exhume trau-
matic memories. In the first two editions of the DSM
(American Psychiatric Association, 1952, 1968), neither
dissociative amnesia nor psychogenic amnesia was
listed or mentioned, although dissociative types of neu-
rosis were. Psychogenic amnesia first appeared in the
third edition of the DSM (American Psychiatric Associa-
tion, 1980; mentioned 19 times). Dissociative amnesia
appeared for the first time in the fourth edition of the
DSM (American Psychiatric Association, 1994; mentioned
50 times). In DSM–5, dissociative amnesia appeared 75
times (American Psychiatric Association, 2013). Interest-
ingly, in no edition of the DSM have the words repress,
repressed memory, or repression been used.

The DSM has codified and widely disseminated the
concept of dissociative amnesia. In some quarters of
psychology and psychiatry, dissociative amnesia is
apparently taken as a valid and totally unproblematic
concept (with notable exceptions; see Pope, Poliakoff,
Parker, Boynes, & Hudson, 2007). Nevertheless, the
definition of dissociative amnesia is scientifically fraught
in many respects, just as is repressed memory. There
are inherent problems when trying to ascertain whether
a trauma has been stored but is nevertheless inacces-
sible. First, there is the complex problem of the lack of
falsifiability: The only way we can determine whether
a memory was stored is by memorial report, but a
memorial report instantly disproves the claim that the
memory is inaccessible. Second, it is difficult to test, or
falsify, whether psychological trauma is the reason why

1080 Otgaar et al.

an event is not remembered. How this is established
depends in part on the theoretical orientation of the
psychologist and whether she or he interprets an inabil-
ity to recall as having been caused by psychogenic
trauma or mundane encoding failures or forgetting
mechanisms.

Indeed, one key question is whether cases that seem
to document dissociative amnesia or repressed memory
can be explained in terms of ordinary memory mecha-
nisms. An example is provided by McNally (2003), who
commented on two alleged cases of dissociative/
psychogenic amnesia in children who had witnessed a
lightning strike. McNally concluded that the memory
loss could plausibly be explained by the fact that

both amnestic youngsters had themselves been
struck by side flashes from the main lightning bolt,
knocked unconscious, and nearly killed. Given the
serious effects on the brain of being knocked
unconscious by lightning, it is little wonder that these
two children had no memory of the event. (p. 192)

The presence of a history of (mild) brain injury in
case descriptions of patients diagnosed with dissocia-
tive amnesia has also been noted by other authors
(Staniloiu & Markowitsch, 2014).

Consider another example that is illustrative of many
similar clinical reports. Harrison et al. (2017) claimed
to have documented 53 cases of, as the authors pre-
ferred to call it, “psychogenic amnesia.” These cases are
cited by others as evidence for the existence of disso-
ciative amnesia (Brand et  al., 2018). Harrison et  al.
(2017) asked the amnesics several questions concerning
their autobiographical memory. Note that none of these
cases adequately satisfied the six tenets of dissociative
amnesia discussed earlier. For instance, amnesia due to
neurological damage, such as “traumatic brain injury”
(American Psychiatric Association, 2013, p. 298), sub-
stance use, or other physical causes were not ruled out,
which would preclude memory loss from being diag-
nosed in the DSM–5 as dissociative amnesia. The pos-
sibility of head injury causing memory impairment is
particularly relevant here, especially because Harrison
et al. found that a history of head injury was common
in the “psychogenic” cases. In addition, Harrison et al.
did not establish whether psychological shock or
trauma caused the reported memory problems or that
any recalled memories really were inaccessible for a
period of time (see also Patihis, Otgaar, & Merckelbach,
2019).

Another issue is that Harrison et al. (2017) did not
exclude the possibility that the dissociative amnesia

Table 2. Side-by-Side Comparisons of the Definitions of Dissociative Amnesia and Repressed Memory

Dissociative amnesia Repressed memory

Repression

DSM–5 (APA, 2013, p. 298) Loftus (1993, p. 518) Holmes (1974, p. 632–633)

“inability to recall autobiographical
information”

[implied indirectly in quotes] “repression is a loss [of memory] which
. . .”

“usually of a traumatic or stressful nature,
that is inconsistent with ordinary
forgetting”

“something happens that is so
shocking. . .”

“is specifically designed to selectively
eliminate from consciousness those
memories which cause the individual
[affective] pain . . . rather than being a
general loss due to simple decay”

“and that it should be successfully
stored”

“that the mind grabs hold of the
memory and pushes it underground”

“material which is repressed is not lost
but rather stored in the unconscious
[emphasis in original]”

“involves a period of time when there is
an inability to recall”

“into some inaccessible corner of the
unconscious. There it sleeps for years,
or even decades, or even forever
isolated from the rest of mental life”

[implied indirectly in quotes]

“not caused by ‘a substance’ or
‘neurological . . . condition’ ”

[implied indirectly]
Implied cause: an event “that is so

shocking”

[implied indirectly]
Implied cause: “repression is a process

motivated by a need to avoid the
disturbing affect associated with
certain memories”

“always potentially reversible because the
memory has been successfully stored”

“Then, one day, it may rise up and
emerge into consciousness”

“the material can return to consciousness
without having to go through the
process of being relearned”

Note: DSM–5 = fifth edition of the Diagnostic and Statistical Manual of Mental Disorders; APA = American Psychiatric Association.

Return of the Repressed 1081

was the result of feigning. This omission is remarkable
because many of the patients with dissociative amnesia
described by these authors were plagued by financial
problems, and it would have been relatively easy to
administer symptom-validity tests to them. With these
tests, one can gauge whether patients endorse atypical
or bizarre symptoms in an attempt to exaggerate their
problems (Lilienfeld, Thames, & Watts, 2013; Peters, van
Oorsouw, Jelicic, & Merckelbach, 2013). Other authors
have found that overreporting of bizarre and implau-
sible symptoms (e.g., “When I hear voices I feel as
though my teeth are leaving my body”) is prevalent
among those who claim dissociative amnesia (Cima,
Merckelbach, Hollnack, & Knauer, 2003). Claiming dis-
sociative amnesia is not the same as suffering from it
(see also Peters et al., 2013). With this consideration in
mind, Staniloiu and Markowitsch (2014) acknowledged
in their review article that “the main challenge posed
by the differential diagnosis of dissociative amnesia is
to distinguish between true and feigned or malingered
amnesia” (p. 237).

Key to our argument is that the evidence that scholars
put forward for dissociative amnesia is typically subject
to more plausible explanations. McNally (2007) listed
several alternative and perhaps more plausible interpre-
tations of the evidence for dissociative amnesia. First,
memory problems that emerge after trauma might be
caused by everyday forgetfulness and should not be
confused with amnesia for the trauma. Second, some
dissociative-amnesia theorists have confused organic
amnesia with dissociative amnesia. Third, people who
have experienced trauma and cannot recollect all of it
might have failed to encode relevant parts of the trau-
matic experience. Fourth, victims of abuse commonly
fail to disclose the abuse (e.g., because they feel
ashamed), a reporting decision that should not be con-
fused with dissociative amnesia. Fifth, when people can-
not recollect any events (even traumatic ones) before
the age of about 3 years old, it likely reflects the well-
established phenomenon of childhood amnesia (Fivush,
Haden, & Adam, 1995; Howe, 2013) rather than dissocia-
tion. Sixth and finally, victims of abuse understandably
often do not want to think about their traumatic experi-
ences but often cannot help it because of flashbacks
and intrusive memories. This phenomenon of suppres-
sion should not be confused with repression, and it falls
well outside the domain of dissociative amnesia.

The Purported Empirical Evidence for
Repressed-Memory Mechanisms

Three main areas of research are typically used to sup-
port repressed memories or dissociative amnesia:
retrieval inhibition, motivated forgetting, and the

relation between trauma and dissociation. Nevertheless,
none of them fully supports all six parts of the defini-
tion of either concept shown in Table 2.

For example, the phenomenon of retrieval inhibition
(M. C. Anderson & Green, 2001; Anderson & Hanslmayr,
2014; M. C. Anderson et al., 2004) suggests that some
mechanism inhibits some memories whereas others
come to consciousness, and that trying not to think
about a memory can make it harder to remember. How-
ever, this phenomenon does not meet the six tenets of
dissociative amnesia, such as the principle that the
event is often traumatic in nature (see also Kihlstrom,
2002). Likewise, some research has shown limbic inhi-
bition via the frontal cortex among individuals with a
subtype of PTSD that involves emotional suppression
(Lanius et  al., 2010). Although interesting, cases of
PTSD involving inhibited emotions do not establish that
a memory is stored, that it is inaccessible because of
trauma and then later becomes accessible. One can
inhibit one’s emotions regarding a painful memory
while retaining a full recollection of this memory.

Other research has shown that alleged cases of dis-
sociative amnesia were accompanied by increased pre-
frontal cortex activity and decreased activation of the
hippocampus when patients were exposed to stimuli
(i.e., certain faces) for which they had reported amnesia
(Kikuchi et al., 2009). However, it would be premature
to interpret this study as evidence for repressed/
dissociated memories. Before concluding that dissocia-
tive amnesia is involved, it is imperative to rule out
other possible plausible explanations, such as feigned
amnesia, which was not investigated in this work. This
is all the more remarkable because one of the patients
who claimed to be amnesic was worried about his
impending marriage, whereas the other patient took a
leave of absence from work after he had been involved
in an accident.

Retrieval inhibition has been suggested to be “a via-
ble model for repression” (M. C. Anderson & Green,
2001, p. 366). The canonical paradigm used to evaluate
retrieval inhibition is the think/no-think paradigm
(M. C. Anderson & Green, 2001). In the original version,
participants see several unrelated word pairs (e.g.,
ordeal-roach). After seeing these stimuli, participants
are presented with cue words (e.g., ordeal) and are
instructed to either recall the associated word (think)
or not (no-think). When participants are asked to recall
all response words during the presentation of cue
words, no-think response words are remembered less
accurately. A meta-analysis showed that no-think words
were associated with lower recall rates than items that
were studied but not asked about during the think/no-
think phase (8% reduction; M. C. Anderson & Huddleston,
2012). One problem with this meta-analysis is that no

1082 Otgaar et al.

unpublished studies from other labs were included,
raising the specter of file-drawer effects and therefore
inflated effect sizes. In fact, Bulevich, Roediger, Balota,
and Butler (2006) conducted three experiments that
failed to replicate the think/no-think memory-suppression
effect and noted that “while working on this project, we
have become aware of other groups of researchers who
have failed to replicate the original M. C. Anderson and
Green (2001) results, although most have given up and
not attempted to publish their results” (p. 1574). Other
memory researchers have recently pointed to unpub-
lished studies that failed to replicate the original think/
no-think finding (A. J. Barnier, personal communica-
tion, November 17, 2018; I. Wessel, personal commu-
nication, January 10, 2019).

Our argument is that the following two research lines
are needed in the area of the think/no-think memory-
suppression effect. First, empirical work is necessary
on the relation between trauma and memory suppres-
sion. To date, there is only limited work in this specific
domain. For example, Hulbert and Anderson (2018)
found that students reporting a greater history of trauma
showed more memory suppression than did students
who reported having little experience with trauma.
Although interesting, this research does not causally
establish whether trauma led to more memory suppres-
sion. Second, a multicenter replication attempt would
yield critical information regarding the robustness, reli-
ability, and potential boundary conditions of the think/
no-think memory-suppression effect.

Motivated forgetting of trauma-related words in the
directed-forgetting paradigm is another technique held
up to support dissociative amnesia (as argued by
DePrince et al., 2012 as part of betrayal trauma theory).
For example, DePrince and Freyd (2001) argued they
had adduced evidence for motivated forgetting in dis-
sociated individuals. In this study, participants scoring
low and high on the dissociative-experiences scale
(DES; E. M. Bernstein & Putnam, 1986) received several
words (trauma-related and neutral) and after each word
were instructed to remember or forget the word. The
authors found that under divided-attention conditions,
participants scoring high on dissociation recalled fewer
trauma-related and more neutral words than those scor-
ing low on dissociation. Still, several other researchers
could not replicate these results (e.g., Devilly et  al.,
2007; Giesbrecht & Merckelbach, 2009; McNally,
Metzger, Lasko, Clancy, & Pitman, 1998). In recent
research, Patihis and Place (2018) found only weak
evidence supporting the hypothesis that traumatized
and dissociated individuals would forget trauma-related
words; only one of eight hypotheses predicted support
for differential motivated forgetting. Patihis and Place
(2018) pointed out the high number of “degrees of

freedom” available to researchers to choose compari-
sons in such directed-forgetting experiments. As they
noted:

Within a given data set, researchers can attempt to
demonstrate differential forgetting between the To
Be Remembered lists and the To Be Forgotten lists.
If that fails they can compare trauma to positive
or neutral words. If that fails they can look for
statistical significance in several interactions—and
they can make all these comparisons with a
number of categorisations: on dissociation, trauma,
diagnosis, acute stress, which all provide additional
degrees of freedom. Given the number of possible
combinations, a motivated researcher will likely
be able to find one comparison that might be
interpreted as motivated forgetting. (p. 630)

Even if this paradigm could consistently reveal that
trauma words are remembered less well by dissociated
individuals, it would not be evidence that a trauma can
be stored and become both inaccessible and ultimately
retrievable with accuracy. Furthermore, there is work
showing that even directed forgetting of autobiographi-
cal memories is not significantly related to the emo-
tional valence of these memories, a finding that runs
counter to the expectation that trauma should lead to
a distinctive repression effect on memory (Barnier
et al., 2007). Despite many assertions in the literature
to the contrary, directed-forgetting research provides
no compelling evidence for repressed memories or dis-
sociative amnesia. On a more general note, researchers
have noted that the memory-impairing effects of
directed forgetting may be due to a lack of rehearsal,
thereby negating the need to invoke repressed memo-
ries (Roediger & Crowder, 1972).

In addition, researchers have heralded the statistical
correlation between trauma and dissociative symptoms
as support for a general theory that trauma can lead to
dissociative amnesia (see Dalenberg et al., 2012, 2014;
but see Lynn et al., 2014). However, even if this relation
is strong—typically it is not (see Patihis & Lynn, 2017)—
this does not establish evidence for dissociative amne-
sia. Dissociation, as measured by the widely used DES,
assesses feelings of depersonalization, derealization,
and memory problems. These symptoms are not
unlikely correlates of being traumatized or stressed for
a period of time. Nevertheless, the DES does not assess
dissociative amnesia as it is defined in the DSM–5,
despite the use of the word “dissociative.” Specifically,
the dissociative-amnesia subscale of the DES (e.g.,
Stockdale, Gridley, Balogh, & Holtgraves, 2002) con-
tains items such as “finding oneself in a place, but
unaware how one got there,” “finding oneself dressed

Return of the Repressed 1083

up in clothes one can’t remember putting on,” “finding
unfamiliar things among one’s belongings,” “not recog-
nizing friends or family members,” and “no memory of
some important personal events (e.g., graduation)”
(E. M. Bernstein & Putnam, 1986; pp. 733–734). These
items do not describe dissociative amnesia and do not
assess reactions to trauma and stored yet inaccessible
memories. Rather, they might reflect poor attentive con-
trol and commonplace cognitive failures. Indeed, studies
have found that in undergraduate samples, scores on the
amnesia items of the DES correlate positively and sig-
nificantly with a measure of poor attentive control—that
is, cognitive failures (Merckelbach, Muris, & Rassin, 1999:
Study 1, r = .49; Study 2, r = .36; see also Merckelbach
et al., 2000); for replication in nonclinical groups, see
Bruce, Ray, and Carlson (2007: r = .31–.46).

The picture we have so far does not imply that dis-
sociation is unrelated to memory. Our position is that
trauma can sometimes lead to feelings of depersonaliza-
tion and that, probably because of accompanying stress
levels, memory problems might arise. However, this
position does not favor the existence of dissociative
amnesia, which implies that memories of entire auto-
biographical experiences have been temporarily inac-
cessible and can later be completely and accurately
recovered (see also Patihis et al., 2019). It is true that
some earlier studies (e.g., Eich, Macaulay, Loewenstein,
& Dihle, 1997) found suggestive evidence for interiden-
tity amnesia in patients with dissociative identity disor-
der (DID). However, a more recent series of studies
by Huntjens and colleagues demonstrated the impor-
tance of distinguishing between what people subjec-
tively report about their memory loss and (the absence
of) objective manifestations of such loss. Huntjens,
Verschuere, and McNally (2012) assessed the transfer
of information between personality states in patients
with a diagnosis of DID. Both tests of explicit and
implicit memory were included, as well as neutral, emo-
tional, and autobiographical information. The data
across studies were consistent in that, subjectively, DID
patients reported amnesia between their personality
states, but objectively, no evidence emerged for interi-
dentity amnesia (e.g., Dorahy & Huntjens, 2007; Huntjens
et al., 2012).

Psychotherapeutic Techniques, Memory
Distortions, and Other Side Effects

We now consider the role of therapy in the emergence
of repressed memories. We discuss research on how
often therapists suggest to clients that they might have
repressed memories, the effects of therapy on (false)
memory, and the link between psychopathology and
(false) memory recovery.

Reports of recovered memories
in therapy

We have shown that a large percentage of clinical psy-
chologists continue to believe that repressed memories
might occur when people are faced with trauma. A
pivotal point here is to know whether such beliefs bear
any ramifications in therapeutic contexts. Patihis and
Pendergrast (2019) surveyed 2,326 U.S. citizens about
memory recovery in psychotherapy. Nine percent (n =
217) of the sample reported that their therapists had
discussed the possibility that they (the client) had
repressed memories of childhood abuse. Furthermore,
those participants were 20 times more likely to report
recovering memories of abuse in therapy (that they
were unaware of before therapy) than participants
whose therapists did not discuss the possibility of
repressed memories. Five percent (n = 122) of the pub-
lic sample reported that in the course of therapy, they
had memories of being abused, of which they had no
previous memory. Therapists who reported recovering
memories engaged in a wide range of therapies, from
attachment therapy to cognitive-behavioral therapy. In
most therapy types, participants indicated a minority
of therapists had discussed the possibility of repressed
memories. For some therapies that involve working
through past trauma, this occurred more frequently
(e.g., attachment therapy, EMDR).

The study by Patihis and Pendergrast (2019) con-
cerned recovered memories in the United States; how-
ever, Shaw, Leonte, Ball, and Felstead (2017) examined
the frequency of repressed and recovered memories in
the United Kingdom. They analyzed cases from the
British False Memory Society, which is a charity that
supports individuals claiming to have been falsely
accused of a crime on the basis of a false memory. The
society database contains more than 2,500 cases since
1993. The researchers selected a random sample from
the database and found that 84.3% (n = 153) of daugh-
ters accusing fathers were said to have undergone a
form of therapy ranging from standard psychotherapy
to hypnosis. Furthermore, Shaw and Vredeveldt (2019)
noted that the Dutch equivalent of the British False
Memory Society, the Fictitious Memory Group, received
13 new possible false-memory cases from 2011 and
2018. Importantly, in 77% (n = 10) of these cases,
alleged victims underwent some form of therapeutic
intervention (e.g., EMDR, reincarnation therapy).

In Germany, a similar false-memory group called
False Memory Deutschland (2019) maintains an archive
containing cases of individuals claiming to have been
falsely accused on the basis of recovered memories of
sexual abuse. This group states on its website that at
the time of the accusations, 83% (n = 81) of alleged

1084 Otgaar et al.

victims had been receiving psychotherapy. Even more
interesting, the number of accusations has increased
since 2002. All in all, reports of repressed memories in
therapy occur on a nontrivial scale and can be found
in many different countries. Of course, here too, the
data should be interpreted with caution because selec-
tion biases might play a role. Still, the data provide
additional evidence that the issue of repressed memo-
ries has not disappeared, and there are even some
indications that that it has made a resurgence, at least
in some areas (see also below).

Therapy and side effects

One of the most important hypotheses underlying the
memory wars was that during psychological treatment,
some therapists suggested to clients that they had
repressed a memory of trauma, which might have
engendered false memories. Although experimental
work has confirmed that suggestive questions can elicit
false memories (Scoboria et  al., 2017), a paucity of
systematic research exists on how therapy shapes mem-
ory. Goodman, Goldfarb, Quas, and Lyon (2017) inves-
tigated whether therapy during a child sexual-abuse
prosecution predicted memory consistency (10–16
years later). Interestingly, the authors found that ther-
apy use positively correlated with memory consistency.
Specifically, alleged victims who received therapy dur-
ing or shortly after the prosecution were more likely to
correctly remember abuse-related details (e.g., name of
the perpetrator, perpetrators’ age) than those who did
not. The use of nonsuggestive psychotherapy may aid
memory consistency rather than hinder it. However,
consistent remembering is not the same as accurate
remembering (Smeets, Candel, & Merckelbach, 2004;
Talarico & Rubin, 2003).

Nevertheless, Goodman et al. (2017) did not specifi-
cally assess whether the type of therapy used was
related to memory accuracy, and no causal conclusions
concerning the effect of therapy on memory accuracy
could be drawn from their study. Establishing a causal
relation is important because some therapies, such as
EMDR and psychoanalytic therapies, rely on patients
retrieving specific autobiographical memories, and
hence there might an increased risk of false memories.
Furthermore, an important issue is whether certain
therapies might increase people’s proneness to acqui-
esce with suggestions and form false memories. Indeed,
Goodman et al. (2017) argued that “a study using an
experimental design with random assignment to groups
to investigate the effects of therapeutic intervention on
true and false memory for traumatic events would be
a welcome contribution to this important field of study”
(p. 929). Houben, Otgaar, Roelofs, and Merckelbach

(2018) addressed this issue by examining the effect of
eye movements as provided in EMDR on false-memory
formation (i.e., reporting of misinformation). Participants
who received eye-movement treatments were more sus-
ceptible to creating false memories than participants who
did not receive eye-movement treatments. Presumably,
eye movements degraded memory, which might make
people more susceptible to accept external misleading
information—which could result in false memories (but
see also van Schie & Leer, 2019). So, although eye move-
ments as in EMDR may improve memory retrieval (e.g.,
Lyle, 2018), they might also increase people’s willingness
to accept external suggestions.

In addition to focusing on the effects of therapy on
memory performance, it is imperative to examine
unwanted side effects of psychotherapy as reported by
the therapists and patients themselves. Although this work
is limited, research has shown that psychotherapy can in
some cases engender negative side effects (Lilienfeld,
2007; Merckelbach, Houben, Dandachi-Fitzgerald, Otgaar,
& Roelofs, 2018; Rozental et al., 2018). Of special inter-
est are studies that examined the relation between
therapy and memory. For example, Rozental, Kottorp,
Boettcher, Andersson, and Carlbring (2016) surveyed
participants who had been in treatment for social anxi-
ety and found that the most frequently endorsed side
effect of treatment was “unpleasant memories resur-
faced” (n = 251; 38%).

Especially relevant are studies examining what hap-
pened after clients recovered memories via therapy.
Fetkewicz, Sharma, and Merskey (2000) noted that sui-
cide attempts increased after patients received recov-
ered-memory therapy, although the absence of a
comparison group of patients who did not receive such
interventions mitigates their conclusions. Loftus (1997)
observed a similar pattern with patients who received
compensation after recovering memories in therapy.
Before memory recovery, 3 patients (10%) reported
thinking about committing suicide, whereas after recov-
ery 20 patients (67%) reported being suicidal. Of course,
it cannot be concluded that this specific therapy caused
these suicide attempts or feelings, but it is concerning
that patients can become more symptomatic after such
therapeutic interventions. Collectively, research on the
negative side effects of therapy, although limited in
quantity, suggests that negative effects of therapy may
not be negligible and that memory recovery may play
a role in deterioration.

Psychopathology and false memory

Another way to examine the role of therapy in the
reported unearthing of repressed memories is to deter-
mine whether people with some form of psychopathology

Return of the Repressed 1085

are at higher risk for false memories than are people
without psychopathology. This information is vital because
people might seek an explanation for their disorder in
therapy (cf. “effort after meaning,” Bartlett, 1932), and
therapists might actively search for such explanations in
patients’ memories and thereby create a springboard for
false memories. Authors have voiced differing opinions
with regard to the relation between psychopathology and
false-memory generation. For example, Bookbinder and
Brainerd (2016) stated that “with respect to PTSD espe-
cially, available data do not provide a consistent picture
of false memory effects” (p. 1345). In contrast, Scoboria
et al. (2017) opined that “people struggling with psycho-
pathology who seek help for their symptoms may be
particularly vulnerable to suggestions” (p. 160).

Otgaar, Muris, Howe, and Merckelbach (2017)
recently reviewed the body of empirical work related
to psychopathology and false-memory creation. Specifi-
cally, they focused on false-memory effects in people
with PTSD, depression, and a history of trauma and
found that in most of these studies, researchers used
the Deese/Roediger-McDermott (DRM) false-memory
paradigm (Deese, 1959; Roediger & McDermott, 1995).
In this paradigm, participants receive word lists contain-
ing associatively related words (e.g., night, pillow,
moon). During recall and recognition tasks, participants
frequently misremember a related but not presented
word called the critical lure (in this case, sleep). Otgaar,
Muris, et  al. (2017) also included experiments that
relied on emotionally charged word lists related to
some aspects of the participants’ psychopathology. For
example, for patients with depression, lists could be
used that focused on the word sad. The general finding
from the review was that people with PTSD, depression,
or a history of trauma were at increased risk of forming
false memories when they received word lists linked to
their symptoms (see also Howe & Malone, 2011). There
is good evidence that certain forms of psychopathology
(e.g., schizophrenia) go hand in hand with a tendency
to accept and give in to external pressure (Peters, Moritz,
Tekin, Jelicic, & Merckelbach, 2012). More importantly,
existing work also indicates that psychopathology (i.e.,
depression, PTSD) is linked to an enhanced propensity
to produce spontaneous false memories.

The implications of this review should be drawn with
care, however, because spontaneous false memories as
induced by the DRM paradigm are typically weakly
related or even unrelated to false memories induced by
suggestion (e.g., D. M. Bernstein, Scoboria, Desjarlais,
& Soucie, 2018; Calado, Otgaar, & Muris, 2019; Nichols
& Loftus, 2019; Ost et al., 2013; Otgaar & Candel, 2011;
Patihis, Frenda, & Loftus, 2018; Zhu, Chen, Loftus, Lin,
& Dong, 2013). So, although psychopathology seems
to be related to an increased vulnerability for

spontaneous false-memory production, this does not
necessarily imply that it is also linked to an increased
susceptibility to suggestion-induced false memories.

The Creation of Implanted False
Memories

Many battles of the memory wars revolved around the
issue of therapists who informed patients that they had
repressed memories of childhood. The fact that some
therapists suggested to patients that they had been
sexually abused raised concerns regarding false memo-
ries in psychotherapy (Loftus, 1994) as well as whether
suggestive therapeutic interventions could fuel false-
memory formation. Focusing on cases in which recov-
ered memories surfaced, researchers began to examine
the conditions, such as the types of events suggested,
under which false events could be inadvertently
implanted in memory. Specifically, a question that was
addressed was whether false events could be implanted
and whether even emotionally negative false memories
could be formed.

False events and implanted false
memories

Researchers have used the false-memory-implantation
paradigm to demonstrate that entire events, ranging
from positive (e.g., a birthday party) to negative (e.g.,
getting lost in a shopping mall), can be implanted. In
the false-memory-implantation paradigm (Loftus &
Pickrell, 1995), participants are asked what they can
remember about a true experienced event and a false
event. Participants are (falsely) told that their parents
confirmed that these events were experienced by the
participants. During multiple suggestive interviews,
about 30% of participants claim to remember the false
event (Scoboria et al., 2017). Studies that have success-
fully implanted negative events bear special relevance
to the claim that recovered memories of abuse may be
instances of rich false memories.

For example, Hyman et  al. (1995) found in their
implantation study that at the second suggestive inter-
view 10% (n = 2) of their subjects falsely remembered
that they spent a night at the hospital because of a high
fever and an ear infection. Loftus and Pickrell (1995)
showed that 25% (n = 6) of their sample created false
memories of being lost in a shopping mall. Porter, Yuille,
and Lehman (1999) implanted several negative events
(i.e., getting lost, serious medical procedure, getting seri-
ously hurt by a child, animal attack, indoor accident),
and percentages of implantation ranged from 16.7%
(n = 3; getting lost) to 36.8% (n = 7; animal attack). Shaw

1086 Otgaar et al.

and Porter (2015) found that 70% (n = 21) of participants
formed false memories of committing a crime (but see
Wade, Garry, & Pezdek, 2018, who used another scoring
method and reported that only 26% to 30% of Shaw and
Porter’s subjects formed false memories).

Of course, the events that have been implanted in
experimental studies on false memories differ in various
ways from recollected events in real cases (e.g., sexual
abuse), which almost always involve feelings of shame
and taboo (Goodman, Quas, & Ogle, 2010). Indeed,
when Pezdek, Finger, and Hodge (1997) attempted to
implant an experience of a rectal enema in adult partici-
pants, none of them fell prey to the suggestion. However,
this is not to say that such events cannot be implanted
in memory. Otgaar, Candel, Scoboria, and Merckelbach
(2010) found that during the second interview, six chil-
dren (10%) falsely reported having received a rectal
enema (see also Hart & Schooler, 2006). Furthermore,
in general, research suggests that negative events are
more likely to be misremembered than are more mun-
dane events (e.g., Otgaar, Candel, & Merckelbach, 2008;
Porter, Taylor, & ten Brinke, 2008). This finding has been
explained by the fact that because emotionally negative
memories contain a high level of connectivity with other
memories, it is relatively easy to activate and then
remember events that were not experienced but related
to the experienced event (e.g., Bookbinder & Brainerd,
2016; Otgaar, Merckelbach, et al., 2017).

Although one could argue that the type of events
implanted in false-memory research do not match
events of interest in legal cases, in false-memory-
implantation studies, participants are generally inter-
viewed two or three times in a suggestive fashion,
whereas legal cases often drive home the point that
people with false memories received suggestive inter-
views by therapists over the course of years (Maran,
2010; van Til, 1997). It seems safe to assume that with
enough suggestive pressure, even extreme negative
events may be implantable in memory.

Estimating the prevalence
of false-memory implantation

Researchers have tried to estimate the percentage of
individuals who develop false autobiographical memo-
ries in the laboratory. Such experiments have mainly
involved healthy undergraduate students who are con-
fronted with suggestive information, after which their
memory reports are evaluated for indications of accept-
ing false information. Attempting to come up with an
accurate estimate is, however, a daunting task because
studies differ in terms of coding and criteria for defining
a report of false memory. Brewin and Andrews (2017)

reviewed false-memory-implantation studies and con-
cluded that in 15% of the recollective experiences
induced by the implantation method, statements were
rated as full-blown false memories. They argued that
this statistic shows that “susceptibility to false memories
of childhood events appears more limited than has
been suggested” (p. 2).

Nevertheless, the review by Brewin and Andrews
(2017) has been criticized (for a critical analysis, see
Otgaar, Merckelbach, et al., 2017). First, as mentioned
previously, the coding of false memories varied among
false-memory-implantation studies. Therefore, Scoboria
et  al. (2017) devised a new coding system based on
theories concerning remembering (e.g., Brewer, 1996;
Conway & Pleydell-Pearce, 2000; Johnson, Hashtroudi,
& Lindsay, 1993; Rubin, 2006). Using this system, they
recoded transcripts from eight published false-memory-
implantation studies. Overall, they found that 30.4% of
transcripts were coded as false memories, which is
twice the percentage that Brewin and Andrews (2017)
reported. In addition, in the analysis by Scoboria et al.,
an additional 23% of cases were coded as having
accepted the false event to some extent.

Second, Otgaar, Merckelbach, et al. (2017) reviewed
15 false-memory laboratory studies that investigated
the confidence that participants place in their false
memories. The data revealed a mean confidence rating
of 74%, with an unweighted 95% confidence interval =
[0.66, 0.78].3 Furthermore, in 93% (k = 14) of the stud-
ies, false-memory reports had confidence ratings
exceeding the midpoint of the rating scale. Clearly,
confidence is often high in implanted false memories.

Third, even if we accept the highly conservative 15%
as a fair estimate of overall false-memory potential, this
percentage still points to a significant problem in legal
and therapeutic settings. It means that if a therapist
using suggestive prompts consulted with 100 patients,
on average, 15 of them might develop illusory autobio-
graphical memories of, for example, sexual abuse, and
some might falsely accuse an innocent person because
of this memory (Nash, Wade, Garry, Loftus, & Ost, 2017;
see also Smeets, Merckelbach, Jelicic, & Otgaar, 2017).

Memory Wars in the Courtroom
and Beyond

We have reviewed several lines of evidence showing
that the topic of repressed memories continues to be
popular although scientifically controversial among
psychologists and psychiatrists. We now examine the
role of repressed memories and dissociative amnesia
in legal cases and the persistence of naive memory
beliefs in the courtroom.

Return of the Repressed 1087

Repressed memories and dissociative
amnesia in the courtroom

In 2017, a French ministerial report was published pro-
posing to increase the statute of limitations for prose-
cuting sexual abuse from 20 to 30 years (Flament &
Calmettes, 2017). The reason given was that because
victims often delay disclosing their abusive experience
(e.g., Goodman-Brown, Edelstein, Goodman, Jones, &
Gordon, 2003; see also Connolly & Read, 2006), they
are still entitled to have their day in court. However, a
more controversial reason for increasing the statute of
limitations given in the report was that traumatic experi-
ences of abuse could lead to dissociative amnesia
(Dodier & Thomas, 2019). Dodier and Thomas rightly
noted that the use of such a controversial term in an
official governmental report might lead people with a
history of trauma to believe that their traumatic memo-
ries are atypical and that to uncover additional memo-
ries they should rely on methods such as recovered
memory therapy that might result in false memories.
Admittedly, victims might take many years to disclose
their traumatic experiences, but as noted before, there
are more plausible explanations than dissociative amne-
sia for the delay in reporting the abuse, such as feeling
ashamed of the trauma and reinterpreting the experi-
ence as abusive (e.g., Goodman-Brown et  al., 2003;
Schooler, 2001). This issue of delayed disclosure is espe-
cially relevant to stress, as there is currently much atten-
tion regarding historic sexual abuse cases, such as those
that emerged in the #MeToo discussion, of which the
overwhelming majority has nothing to do with memory
repression or recovery (see also Goodman et al., 2017).

There is also evidence of recovered memories enter-
ing into some cases in the United Kingdom. The UK

Advocate’s Gateway (2015) document on trauma
explains to lawyers how to approach traumatized wit-
nesses and victims. It stipulates that dissociative amne-
sia is possible and argues that “Trauma disrupts the left
hemisphere function of the brain. . . . This disruption
affects the ability to give a verbal narrative. . . . The
right hemisphere of the brain stores implicit or sensory
associated memories” (p. 5). This is questionable advice,
with some potentially unsupported and pseudoscien-
tific ideas mixed into the document.

An alternative way to examine whether the issue of
repressed memories and dissociative amnesia is still
prominent in the legal arena is to examine court pro-
ceedings and investigate the number of cases in which
repressed memories played a role. In the Netherlands,
an online database of court rulings (http://www.recht
spraak.nl) exists in which one can search for key terms
in a diverse set of cases. The database is not exhaustive
in that it only lists the most prominent court rulings.
We used the search term verdringing (“repression”) and
investigated criminal trials from 1990 to 2018 in which
repressed memories were mentioned. Figure 1 demon-
strates that cases in which this term was used referring
to cases on repressed memories have increased over
the past years. When a similar exercise was performed
using the search term hervonden herinnering (“recov-
ered memory”), a similar pattern emerged. Moreover,
when we used the term dissociatieve amnesia (“dis-
sociative amnesia”), again, we found that this term is
on the rise.4

Caution should be exerted when interpreting these
data. First, it is remarkable that virtually no legal cases
were found on repression and recovered memory from
1990 to 2000. One reason might be that such older cases
are not represented in this database. Second, although

0

5

10

15

20

25

30

35

1990–2000 2001–2010 2011–2018

Nu
m

be
r o

f C
as

es

Repression

Recovered Memory

Dissociative Amnesia

Fig. 1. Number of Dutch legal cases mentioning repression, recovered memory, or dissocia-
tive memory from 1990 to 2018.

http://www.rechtspraak.nl

http://www.rechtspraak.nl

1088 Otgaar et al.

issues such as repressed and recovered memories were
discussed in these criminal trials summarized by perti-
nent court rulings thereafter, judges did not necessarily
accept these notions uncritically. Nonetheless, these
data demonstrate that, at least in the Netherlands, legal
professionals still use the Freudian and neo-Freudian
nomenclature of repression and dissociative amnesia.

Memory beliefs in the courtroom

Although we have discussed naive beliefs about mem-
ory across a variety of lay and professional populations,
these beliefs can be especially problematic in the court-
room. Because judicial outcomes may be influenced by
the naive beliefs about memory that triers of fact har-
bor, it is critical that when testimony consists mainly of
memory evidence (e.g., remembering event details,
identifying the perpetrator), actors in the legal domain
possess a scientifically informed view of how memory
works.

To appreciate how the disconnect between the sci-
ence of memory and the beliefs held by individuals in
the legal arena can lead to unsafe convictions, one can
examine the cases listed on the Innocence Project web-
sites in the United States (http://www.innocenceproject
.org) and the United Kingdom (http://www.innocen
cenetwork.org.uk). The most common factor in these
false convictions has been faulty memory evidence (i.e.,
incorrect eyewitness identifications are implicated in
more than 70% of cases). Police and prosecutors appar-
ently made decisions about this memory evidence per-
haps without exactly understanding the science of how
memory works and often because other more objective
evidence was lacking (for reviews, see Howe & Knott,
2015; Howe, Knott, & Conway, 2018).

Judges and prosecutors alike differ as to whether
they will accept expert memory testimony. For example,
in a Dutch revision case in which dissociative memories
of abuse were the central issue, one senior prosecutor
opined that in contrast to DNA experts, psychological
experts do not aid judges in helping them to understand
the intricacies of statements by witnesses or defendants
(https://uitspraken.rechtspraak.nl/inziendocument?id=
ECLI:NL:PHR:2015:2769). He added that the field of
legal psychology is known for its lack of consensus and
for its high degree of subjectivity, which is hyperbolic
when one looks at the generally broad consensus on
a range of topics found in surveys among legal psy-
chologists (Kassin, Redlich, Alceste, & Luke, 2018;
Kassin et al., 2001). Furthermore, research clearly indi-
cates that judges routinely overestimate jurors’ ability
to understand and correctly use memory evidence
when in fact it is based solely on their “common
sense”—such as that memory works like a video camera

(e.g., Houston, Hope, Memon, & Read, 2013; Magnussen
et  al., 2010); for the Scooter Libby effect, see also
Kassam, Gilbert, Swencionis, & Wilson, 2009).

The question of whether jurors’ commonsense views
of memory in court are adequate also extends to cases
in which adults are recollecting events that happened
decades earlier in childhood. As elsewhere, it is not a
given that judges will necessarily accept scientific
expert testimony about memory in their courtroom to
counteract the commonsense views held by jurors and
others involved in the judicial system. Progress has
been made in some U.S. states in which judges in trials
involving eyewitness identification must now present
jurors with cautions about the reliability of such evi-
dence before their deliberation (State of New Jersey v.
Henderson, 2011). In Pennsylvania, Loftus, Francis, and
Turgeon (2012) drafted jury instructions that addressed
issues concerning a broad spectrum of expert memory
testimony. Likewise, in the United Kingdom, judges are
now obligated to give juries so-called Turnbull guide-
lines in the cases that heavily rely on eyewitness iden-
tification (Trevelyan, n.d.). Admittedly, these are but a
few recent examples, and much more research needs
to be conducted to counteract the impact of erroneous
lay beliefs about memory in the courtroom.

Furthermore, it is also imperative that such guide-
lines are not fixed but are provisional and can be
updated any time. Guidelines are ideally based on the
current corpus of scientific findings, but new findings
might warrant amendments. For example, previous
research has suggested that the confidence that eyewit-
nesses place in their identification is only weakly
related to their accuracy. In contrast, recent research
has demonstrated that under optimal conditions, con-
fidence is strongly predictive of accuracy (Sauerland &
Sporer, 2009; Wixted & Wells, 2017). It is important to
be cognizant about such new developments.

Memory wars in the scientific literature

One might posit that although the controversial issue
of repressed memories is still relevant in clinical and
legal contexts, the debate concerning repressed memo-
ries is now muted in the scientific literature. There are
two indications that this is not the case. First, in a recent
bibliometric analysis, Dodier (2019) examined the num-
ber of publications and citations regarding repressed
and recovered memories from 2001 to 2018. The author
found that proponents and opponents of repressed
memories have continued to publish articles about
repressed and recovered memories throughout the time
period. Notably, these articles were cited just as often
as articles published during the presumed heyday of
the memory wars in the 1990s. In addition, the year

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Return of the Repressed 1089

2018 witnessed an increase in publications on this
topic. This increase was characterized by a mix of arti-
cles in favor or against the concept of repressed memo-
ries. Specifically, of the 16 articles in 2018, 5 (31%) were
largely or entirely in favor of the existence of repressed
memories, whereas 9 (56%) articles expressed skepti-
cism regarding the existence of repressed memories
(two articles adopted a neutral position).

Second, the debate over repressed memories and
dissociative amnesia has hardly vanished from the sci-
entific literature. For example, Brand, Schielke, and
Brams (2017) and Brand, Schielke, Brams, and DiComo
(2017) recently tried to provide legal professionals with
evidence-based knowledge on trauma-related dissocia-
tion and concomitant effects such as dissociative amne-
sia. Their articles provoked a disagreement between
them and memory researchers who argued that their
conclusions were not based on evidence and poten-
tially hazardous (Brand et  al., 2018; Merckelbach &
Patihis, 2018; Patihis et al., 2019). Debates relating to
the issue of dissociative amnesia, repressed memories,
or both, are clearly alive and well in the scientific lit-
erature (see also Staniloiu & Markowitsch, 2014).

Conclusion

The claims of some authors to the contrary, the contro-
versial topic of repressed memories and dissociative
amnesia continues to be very much alive in clinical,
legal, and academic contexts. Converging lines of evi-
dence suggest that concerns regarding the widespread
belief in repressed memories are far from having been
resolved following the memory wars of the 1990s.
Across many different professionals (e.g., psychothera-
pists), the percentage who believe in repressed memo-
ries remains high, generally above 50%. Furthermore,
the idea of repressed memories has merely become
popular under a different name—dissociative amnesia—
which shares many characteristics with repressed mem-
ory and that carries the added cachet of being associated
with the DSM–5 (American Psychiatric Association,
2013). In addition, research points to the possibility that
some therapeutic techniques exert adverse effects by
potentially increasing the likelihood of false memories.
Finally, questions of repressed memories continue to
be addressed in the courtroom and in the scientific
literature. Taken together, these different threads of
evidence imply that falsely recovered memories of
abuse continue to pose a substantial risk in therapeutic
settings, potentially leading to false accusations and
associated miscarriages of justice.

A relevant question is how flawed ideas regarding
the functioning of memory could be corrected. That
unconscious repressed memory is still accepted with

little qualification and remains popular among many
mental-health professionals can be explained in part
by the now well-replicated finding that it is typically
difficult to correct erroneous beliefs. Specifically, when
people are confronted with any form of misinformation
(e.g., fake news), correcting such errors is challenging,
a phenomenon referred to as the continued-influence
effect (Lewandowsky, Ecker, Seifert, Schwarz, & Cook,
2012; see also Lilienfeld, Marshall, Todd, & Shane, 2014)
or belief perseverance (C. A. Anderson, Lepper, & Ross,
1980). However, recent studies suggest that informing
people that their firmly held beliefs are incorrect (“pre-
bunking”), and even providing them with the correct
alternative information (debunking), can often be effec-
tive in correcting these beliefs (e.g., Blank & Launay,
2014; Crozier & Strange, 2019). In addition to applying
these provisional but promising methods, it is crucially
important to educate individuals, especially legal pro-
fessionals and clinicians, about the science of memory.
This effort is all the more essential given that these
professionals are often in close contact with victims,
patients, witnesses, and suspects. Such interactions are
a prime opportunity for inadvertent memory contami-
nation. Increasing their awareness of potentially harm-
ful beliefs about repressed memories should therefore
be a priority in clinical and legal work as well as for
psychological scientists at large.

Action Editor

Laura A. King served as action editor for this article.

ORCID iDs

Henry Otgaar https://orcid.org/0000-0002-2782-2181
Lawrence Patihis https://orcid.org/0000-0003-2870-8986

Declaration of Conflicting Interests

The author(s) declared that there were no conflicts of interest
with respect to the authorship or the publication of this
article.

Notes

1. We use the term false memory in this article to refer to the
remembrance of events/details that did not occur (e.g., Loftus,
2005).
2. On the website of the Journal of Trauma & Dissociation, we
looked for articles using the search term “dissociative amnesia”
from January 2010 to May 2019 and from January 1990 to May
1999.
3. In the reviewed studies, confidence was measured using dif-
ferent rating scales (e.g., 1–5, 1–10, 50–100).
4. We explored whether the rise of these terms is also evident
when controlling for the total number of cases in the Dutch
legal database. From 2001 to 2010, there were a total of 192,345
cases, and from 2011 to 2018 there were a total of 267,377

https://orcid.org/0000-0002-2782-2181

https://orcid.org/0000-0003-2870-8986

1090 Otgaar et al.

cases. Even if these base rates were taken into account, we
found that the terms recovered memory (9 × 10−5 to 1.2 × 10−4)
and dissociative amnesia (7 × 10−5 to 1 × 10−4) increased from
2001 to 2010 to 2011 to 2018.

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J Sleep Res. 2022;31:e13527. wileyonlinelibrary.com/journal/jsr  | 1 of 12
https://doi.org/10.1111/jsr.13527

1  |  INTRODUC TION

Previous studies report that false memories can be influenced by
sleep (for a review see Conte & Ficca, 2013; Landmann et al., 2014).
Among the first to investigate the relationship between sleep and
false memories, Diekelmann, Born, and Wagner (2010), Diekelmann,
Landolt, Lahl, Born, and Wagner (2008) showed that sleep- deprived

individuals produce more false memories at morning re- test com-
pared to participants in an undisturbed sleep condition. The au-
thors specified that this effect could be mainly linked to an impaired
memory retrieval process. In fact, acute sleep loss can affect several
cognitive functions related to prefrontal activity that are essential
to accurate recall from long- term memory (Durmer & Dinges, 2005;
Frenda & Fenn, 2016).

Received: 28 June 2021  | Revised: 16 November 2021  | Accepted: 18 November 2021
DOI: 10.1111/jsr.13527

R E S E A R C H A R T I C L E

False memories formation is increased in individuals with
insomnia

Serena Malloggi1  | Francesca Conte2  | Oreste De Rosa2  | Stefania Righi1  |
Giorgio Gronchi1  | Gianluca Ficca2  | Fiorenza Giganti1

1Department of NEUROFARBA,
University of Florence, Florence, Italy
2Department of Psychology, University of
Campania L. Vanvitelli, Caserta, Italy

Correspondence
Serena Malloggi, Department of
NEUROFARBA, University of Florence,
Via di San Salvi 12, 50135, Florence, Italy.
Email: serena.malloggi@unifi.it

Funding information
V:ALERE 2019

Summary
Previous studies suggest that sleep can influence false memories formation.
Specifically, acute sleep loss has been shown to promote false memories production
by impairing memory retrieval at subsequent testing. Surprisingly, the relationship
between sleep and false memories has only been investigated in healthy subjects
but not in individuals with insomnia, whose sleep is objectively impaired compared
to healthy subjects. Indeed, this population shows several cognitive impairments
involving prefrontal functioning that could affect source monitoring processes and
contribute to false memories generation. Moreover, it has been previously reported
that subjects with insomnia differentially process sleep- related versus neutral stimuli.
Therefore, the aim of the present study was to compare false memories production
between individuals with insomnia symptoms and good sleepers, and to evaluate
the possible influence of stimulus category (neutral versus sleep- related) in the two
groups. The results show that false memories are globally increased in participants re-
porting insomnia symptoms compared to good sleepers. A reduction in source moni-
toring ability was also observed in the former group, suggesting that an impairment
of this executive function could be especially involved in false memories formation.
Moreover, our data seem to confirm that false memories production in individuals
with insomnia symptoms appears significantly modulated by stimulus category.

K E Y W O R D S
Deese– Roediger– McDermott (DRM) paradigm, false memory, insomnia disorder, sleep- related
stimuli

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2 of 12  |     MALLOGGI ET AL.

Most of the available studies on sleep and false memories have
been conducted on healthy subjects exposed to experimental sleep
deprivation (see Diekelmann et al., 2008, 2010 or restriction e.g. Lo,
Chong, Ganesan, Leong, & Chee, 2016), while clinical samples have
been neglected. As there is growing acceptance that the nature and
severity of the cognitive consequences of these experimental sleep
interventions differ from those reported in chronic sleep disorders
(Shekleton, Rogers, & Rajaratnama, 2010), we intended to assess the
effect of chronically disturbed sleep on false memories production.

Insomnia is a sleep disorder characterised by subjective com-
plaints of non- restorative sleep and of difficulties in initiating and/
or maintaining sleep, accompanied by decreased daytime func-
tioning, which persist in time (American Psychiatric Association,
2013). Objective sleep impairments are also often reported in this
population, such as changes in sleep architecture (i.e. reduction in
slow- wave sleep and rapid eye movement [REM] sleep duration)
compared to healthy subjects (Baglioni et al., 2014). Moreover, indi-
viduals with insomnia show several cognitive impairments that could
contribute to false memories generation. It has been observed that
they perform more poorly than good sleepers on complex cognitive
tasks depending on the efficiency of the prefrontal cortex, e.g. in
tests assessing working memory (e.g. retention and manipulation
of previously acquired information), problem solving, information
processing, and selective attention (for a review see Fortier- Brochu,
Beaulieu- Bonneau, Ivers, & Morin, 2012).

Other factors are likely to modulate the effects of disordered
sleep on false memories production. For instance, an important
one could be the nature of the administered stimuli. Indeed, several
studies report that individuals with insomnia preferentially focus
their attention on stimuli that are related to sleep, which appear to
them more salient than neutral ones (Espie, Broomfield, MacMahon,
Macphee, & Taylor, 2006; Harvey, 2002). This phenomenon is
known as “attentional bias” and has been previously observed in this
population through specific cognitive tasks, such as the Stroop task
(Spiegelhalder, Espie, Nissen, & Riemann, 2008; Zhou et al., 2018),
the dot probe task (MacMahon, Broomfield, & Espie, 2006), prim-
ing tasks (Giganti et al., 2017), and eye- tracking paradigms (Woods,
Scheepers, Ross, Espie, & Biello, 2013). Overall, these studies sug-
gest that sleep- related stimuli induce a higher activation in individ-
uals with insomnia relative to good sleepers, leading the former to
respond differently to these stimuli. For instance, it has been ob-
served that individuals with insomnia, compared to good sleepers,
show slower reaction times for sleep- related stimuli at the Stroop
task (Spiegelhalder et al., 2008; Zhou et al., 2018) and that they rec-
ognise these stimuli at lower spatial frequencies in a priming task
(Giganti et al., 2017). Instead, the effect of stimulus category has
not yet been investigated in tasks based on semantically associated
items, such as the Deese– Roediger– McDermott paradigm (DRM;
Roediger & McDermott, 1995).

A complementary hypothesis has been sometimes put forward
(e.g. Williams, Mathews, & MacLeod, 1996) that the attentional
bias may reflect the way in which “experts” react to their expertise-
related stimuli when performing specific tasks. A few studies

actually show that experts generally produce higher rates of false
memories for words that are related to the domain of their expertise
compared to non- experts (Baird, 2003; Castel, McCabe, Roediger, &
Heitman, 2007). This finding is attributed to the stronger semantic
activation occurring in experts: in the case of DRM word lists, ex-
pertise would increase the number and strength of associations be-
tween expertise- related terms and enhance the spreading activation
to include the non- presented critical words.

In light of this literature, the investigation of the effects of stimu-
lus category in a DRM task in individuals with insomnia, who may be
considered “experts” and strongly activated by the theme of sleep
(Espie et al., 2006; Harvey, 2002), appears particularly interesting.

The first aim of the present study was to assess whether chronic
poor sleep quality in subjects with insomnia affects false memories
production. To this end, we compared performance at the DRM par-
adigm (Roediger & McDermott, 1995) between a group of individu-
als showing insomnia symptoms and one of good sleepers. In light of
literature on the attentional bias described in people with insomnia
(Giganti et al., 2017; Harris et al., 2015), we also evaluated the possible
effect of stimulus category by comparing performance at neutral and
sleep- related word lists included in the DRM task. Finally, consider-
ing the association between false memories production and executive
functioning (e.g. Leding, 2012; Peters, Jelicic, Verbeek, & Merckelbach,
2007), as well as the observed impairments of these functions in in-
somnia (for example see Haimov, Hanuka, & Horowitz, 2008; Joo et al.,
2013), we assessed in both groups working memory, inhibitory control
and source monitoring ability, the latter being considered as especially
linked to false memories formation (Mitchell & Johnson, 2000).

2  |  METHODS

2.1  |  Participants and procedure

A total of 80 potential participants were approached at university
sites (i.e. lecture halls, library, etc.) and asked to complete a set of
screening questionnaires: the Pittsburgh Sleep Quality Index (PSQI;
Italian version from Curcio et al., 2013), Insomnia Severity Index
(ISI; Italian version from Castronovo et al., 2016), Sleep Disorder
Questionnaire (SDQ; Violani, Devoto, Lucidi, Lombardo, & Russo,
2004), Beck Depression Inventory II (BDI- II; Italian version from
Sica & Ghisi, 2007), and Beck Anxiety Inventory (BAI; Italian version
from Sica & Ghisi, 2007) described in detail below. In addition, they
were administered a semi- structured interview at the sleep labora-
tory, conducted by a licensed psychologist who had received spe-
cific training, in order to assess general medical condition and health
habits, presence of psychiatric disorders and sleep disorders. The
presence of clinical insomnia was specifically addressed by means of
the semi- structured interview (Morin, 1993).

Based on scores at the screening instruments and on the inter-
view, 53 university students were recruited for the study and in-
cluded in either the “good sleep group” (GS Group, n = 28) or the
“insomnia group” (IN Group, n = 25). Inclusion criteria common to

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    |  3 of 12MALLOGGI ET AL.

both groups were: absence of any relevant somatic or psychiatric
disorder; absence of clinically significant depression and anxiety
symptoms (BDI- II score ≤29; BAI score ≤25); no history of drug or al-
cohol abuse; absence of sleep disorders (other than insomnia for the
IN Group) and of any sleep apnea or respiratory disorder symptom;
having a regular sleep– wake pattern (e.g. individuals with irregular
study or working habits such as shift- working were excluded); no use
of psychoactive medication or alcohol at bedtime. In addition, for
inclusion in the IN Group, participants had to score ≥5 at the PSQI,
≥8 at the ISI and to be classified as presenting “clinically significant
insomnia” at the SDQ; further, they had to fully meet Diagnostic and
Statistical Manual of Mental Disorders, fifth edition (DSM- 5) criteria
for Insomnia Disorder, as verified through the interview. Finally, in-
clusion in the GS Group was based on: PSQI score <5, ISI score <8, being classified as a “good sleeper” at the SDQ, and absence of any sleep disorder as also verified through the interview.

The two groups did not differ for age, gender distribution, cir-
cadian preference (measured through the reduced version of the
Morningness– Eveningness Questionnaire; Italian version from
Natale, Esposito, Martoni, & Fabbri, 2006) and daytime sleepi-
ness (measured through the Epworth Sleepiness Scale; Italian ver-
sion from Vignatelli et al., 2003). Instead, as expected, significant
between- group differences emerged in several habitual sleep fea-
tures assessed through the PSQI, such as bedtime, sleep duration
and sleep onset latency, as well as in PSQI global scores (Table 1).

Participants were requested to complete a sleep diary on the day
of the DRMs testing session, in order to control that they performed
the task after a night of sleep that was representative of their habit-
ual sleep. In Table 2 we report the sleep measures of the night before
the administration of the memory task in both groups.

All selected participants were individually invited to the sleep
laboratory, where they were administered the DRM paradigm
(Roediger & McDermott, 1995).

On separate days, a subsample of 17 participants from
the IN Group (eight males and nine females; mean [SD] age of
24.5 [2.2] years) and 21 from the GS Group (eight males and 13
females; mean [SD] age of 24.1 [2.2] years) were again invited in-
dividually to the sleep laboratory where they were administered a
set of cognitive tests to evaluate executive functioning and source
monitoring ability. Table 3 lists demographic characteristics, circa-
dian preference, daytime sleepiness and habitual sleep features of
the subsample. All testing sessions (both the DRM and the exec-
utive functioning tasks) were performed in the morning, between
11:00 a.m. and 1:00 p.m., by an experimenter who was blind to the
study group.

There was no money or credit compensation for participating in
the study.

The study design was submitted to the Ethical Committee of the
Department of Psychology, University of Campania “L. Vanvitelli”,
which approved the research (code 22/2020) and certified that the
involvement of human participants was performed according to ac-
ceptable standards.

2.2  |  Screening instruments

1. The PSQI (Italian version from Curcio et al., 2013), a self- report
questionnaire evaluating subjective sleep quality in the past
month. It is composed of 19- items grouped into seven sub-
scales: Subjective Sleep Quality, Sleep Latency, Sleep Duration,
Habitual Sleep Efficiency, Sleep Disturbances, Use of Sleep
Medication and Daytime Dysfunctions due to sleepiness. The
PSQI total score ranges from 0 to 21, with higher scores
indicating sleep difficulties and lower sleep quality. The cut-
off score of ≥5 is adopted to discriminate between good and
bad sleepers.

TA B L E 1 Age, gender distribution, circadian preference, daytime sleepiness, habitual sleep features and sleep quality in the insomnia
group (IN Group) and good sleep group (GS Group)

Variable IN Group GS Group Statistical test

Age, years, mean (SD) 25.16 (4.34) 24.10 (3.17) U = 278.50, p = 0.19

Gender, male/female, n 13/12 11/17 χ2 = 0.86, p = 0.862

MEQr score, mean (SD) 13.00 (2.61) 14.54 (3.18) U = 245.00, p = 0.06

ESS score, mean (SD) 7.64 (2.82) 6.32 (3.28) U = 253.00, p = 0.11

Habitual bedtime, hh:mm, mean (SD) 00:32 (00:52) 23:32 (00:59) U = 91.50, p = 0.001

Habitual rise time, hh:mm, mean (SD) 08:08 (01:04) 07:32 (01:23) U = 182.50, p = 0.233

Habitual sleep duration, hh:mm, mean (SD) 06:27 (00:59) 07:41 (00:48) U = 78.50, p < 0.001

Habitual sleep onset latency, hh:mm, mean (SD) 00:25 (00:13) 00:11 (00:05) U = 116.00, p < 0.001

PSQI global score, mean (SD) 8.16 (2.26) 3.21 (0.87) U = 0.000, p < 0.001

ESS, Epworth Sleepiness Scale; GS Group, good sleep group; IN Group, insomnia group; MEQr, Morningness– Eveningness Questionnaire (reduced
version); PSQI, Pittsburgh Sleep Quality Index.
Habitual bedtime, rise time, sleep duration and sleep onset latency were collected through the PSQI. Mann– Whitney U is reported for between-
groups comparisons for all variables except gender. Results of the chi- squared test are reported for differences in gender distribution.

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4 of 12  |     MALLOGGI ET AL.

2. The ISI (Italian version from Castronovo et al., 2016), assessing
the severity of insomnia symptoms during the previous 2 weeks.
Based on the scores, subjects are classified into four categories:
(a) no clinically significant insomnia (score 0– 7); (b) subthreshold
insomnia (8– 14); (c) clinical insomnia – moderate severity (score
15– 21); (d) clinical insomnia – severe (22– 28).

3. The SDQ (Violani et al., 2004) is a self- rating questionnaire with 27
items evaluating the presence of different sleep problems in the last
month. The first three questions concern symptoms of insomnia,
while the others investigate the presence of excessive sleepiness,
sleep apnea, parasomnias, and snoring. A subsequent set of ques-
tions investigates the duration, frequency, and consequences of the
sleep problem, and is used for the evaluation of the severity of the
sleep disturbances reported. The SDQ permits the classification of
subjects into three main categories: subjects who do not complain
of any sleep disorder; subjects who report the occurrence of sub-
threshold insomnia and subjects with clinically significant insomnia.

4. The BDI- II (Italian version from Sica & Ghisi, 2007) assesses the se-
verity of depressive symptoms. It comprises 21 items and the total
score ranges from 0 to 63, with higher scores indicating more severe
depressive symptoms. Particularly, scores 0– 13 represent minimal

depression, scores 14– 19 mild depression, scores 20– 28 moderate
depression, and scores 29– 63 severe depression symptoms.

5. The BAI (Italian version from Sica & Ghisi, 2007), a self- report in-
strument assessing the presence and severity of anxiety symp-
toms in the past week. It comprises 21 items measuring the
intensity of common somatic and cognitive symptoms of anxiety
through a Likert scale ranging from 0 (Not at all) to 3 (Severely – it
bothered me a lot). The score range is 0– 63, with higher scores in-
dicating more severe anxiety symptoms: specifically, a total score
of 0– 7 is considered to index minimal severity, 8– 15 mild, 16– 25
moderate, and 26– 63 severe.

2.3  |  False memories task

In the classical DRM paradigm (Roediger & McDermott, 1995), an
immediate free recall test is administered on a list of words that
are semantically associated to an unstudied critical word (e.g. “ink”,
“paper”, “school”, all related to “pen”). This task reliably produces
high rates of false memories for unstudied critical lures (Roediger &
McDermott, 1995).

TA B L E 2 Sleep features of the night preceding the DRM task session in the insomnia group (IN Group) and good sleep group (GS Group)

Variable IN Group GS Group Statistical test

Bedtime, hh:mm, mean (SD) 00:42 (00:47) 23:46 (00:55) U = 85.50, p = 0.003

Rise time, hh:mm, mean (SD) 07:50 (01:01) 07:48 (00:51) U = 219.50, p = 0.98

Sleep duration, hh:mm, mean (SD) 06:47 (01:01) 07:52 (01:06) U = 0.004, p = 0.004

Sleep onset latency* 3 (i.e. “≥15 min”) 2 (i.e. “10 min”) U = 202.00, p = 0.010

Number of awakenings, mean (SD) 1.2 (1.18) 0.53 (0.83) U = 235.50, p = 0.025

Rise time latency* 2 (i.e. “10 min”) 1 (i.e. “5 min”) U = 206.00, p = 0.019

Sleep features were collected through sleep logs. Mann– Whitney U is reported for between- groups comparisons for all variables. An asterisk (*)
indicates median values. Prior night’s sleep onset latency was obtained through the question: “How long did it take you to fall asleep last night?”
(“<5 min”, “5 min”, “10 min”, “≥15 min”). Rise time latency was obtained through the question: “How long did it take you to rise from bed after this morning's awakening?” (“<5 min”, “5 min”, “10 min”, “≥15 min”).

TA B L E 3 Age, gender distribution, circadian preference, daytime sleepiness, habitual sleep features and sleep quality in participants of
the subsample

Variable IN Group GS Group Statistical test

Age, years, mean (SD) 24.53 (2.18 24.10 (3.56) U = 143.00, p = 0.31

Gender, male/female, n 8/9 8/13 χ2 = 0.310, p = 0.578

MEQr score, mean (SD) 12.82 (2.51 14.52 (3.61) U = 127.50, p = 0.136

ESS score, mean (SD) 8.35 (3.58 6.57 (3.52) U = 119.00, p = 0.08

Habitual bedtime, hh:mm, mean (SD) 00:36 (00:49 23:21 (00:40) U = 27.50, p < 0.001

Habitual rise time, hh:mm, mean (SD) 07:51 (01:14 07:23 (00:51) U = 87.00, p = 0.305

Habitual sleep duration, hh:mm, mean (SD) 06:22 (00:59 07:39 (00:48) U = 33.50, p = 0.001

Habitual sleep onset latency, hh:mm, mean (SD) 00:27 (00:14 00:10 (00:04) U = 41.00, p <0.001

PSQI global score, mean (SD) 8.35 (3.58 3.19 (0.98) U = 0.000, p ≤ 0.001

ESS, Epworth Sleepiness Scale; GS Group, good sleep group; IN G, insomnia group; MEQr, Morningness– Eveningness Questionnaire (reduced
version); PSQI, Pittsburgh Sleep Quality Index.
Habitual bedtime, rise time, sleep duration and sleep onset latency were collected through the PSQI. Mann– Whitney U is reported for between-
groups comparisons for all variables except gender. Results of the chi squared test are reported for differences in gender distribution.

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    |  5 of 12MALLOGGI ET AL.

In order to highlight the possible effect of stimulus category, here
we adopted, as in Baird (2003), a reduced version of the DRM para-
digm (Roediger & McDermott, 1995) consisting in the presentation
of four- word lists made up of 15 words each. Indeed, as observed in
a recent meta- analysis (Newbury & Monaghan, 2019), the length of
the lists rather than their number appears to significantly affect false
recall rates (with longer lists producing greater false recall).

The sleep- related list used in this study (i.e. the one correspond-
ing to the unpresented lure “sleep”) was created ad hoc in Italian
following the method used by Iacullo and Marucci (2016), due to the
absence of any such standardised list in Italian. Thus created, the list
was preliminarily presented to 30 university students (21 females
and nine males; mean [SD] age of 24.10 [4.06] years), not enrolled
in the present study, to assess the false recall rate for it (which was
27%). Then, we selected from Iacullo and Marucci (2016) the three
lists showing the most similar false recall rates. The selected lists,
corresponding to the lures “flag”, “pen”, and “river”, all showed a false
recall rate of 21%. Furthermore, in order to test possible differences
between our sleep- related list and the neutral one, 25 individuals
(16 females and nine males; mean [SD] age of 25.88 [3.23] years),
who were not enrolled in the main study, were asked to rate on a 1– 5
Likert scale the sleep- relatedness, familiarity, activation and valence
of each word belonging to the two lists, as well as their respective
critical lures. Comparisons between the two lists revealed no sig-
nificant difference for familiarity (t = −1.00, p = 0.33), activation
(t = 0.57, p = 0.57) or valence (which was judged as neutral for both
lists; t = −1.31, p = 0.20), whereas a significant difference emerged
for sleep- relatedness (t = −17.6, p ≤ 0.001).

As in Roediger and McDermott (1995) and Iacullo and Marucci
(2016), the words in each list were presented in order of associative
strength with the unpresented lure (from strongest to weakest).

As for task administration, the experimenter read the lists aloud
with an interval of 20 s between lists. Participants were instructed
to memorise the words as accurately as possible and were informed
that they would be tested on them later. The “flag” and “river” lists
(List 1 and 4, respectively), here used to control for primacy and re-
cency effects as in Baird (2003), were presented to all participants as
the first and last list of the set, respectively. The order of presenta-
tion of the “pen” and “sleep” lists (List 2 and 3, respectively), instead,
was balanced between subjects (Baird, 2003).

After the “river” list was presented, participants performed the
free recall test. Specifically, they were requested to write down on
a blank piece of paper as many words as possible from all the pre-
sented lists. They were allotted 5 min for recall. In order to hold re-
call time constant between subjects, participants were instructed to
continue thinking about the words for the whole allotted time.

2.4  |  Executive functioning tasks

For the assessment of executive functioning we employed classical
tasks that measure the main executive components (e.g. Denckla,
1994; Miyake et al., 2000): specifically, working memory was

evaluated through the Working memory subtests of the Wechsler
Adult Intelligence Scale, fourth edition (WAIS- IV; Wechsler, 2008)
and inhibitory control was tested through the Stroop task (Stroop,
1935). In addition, we created an ad hoc task aimed to evaluate
source monitoring ability, which is deemed to be specifically linked
to false memories formation (Mitchell & Johnson, 2000).

1. Working memory subtests of the WAIS- IV (Wechsler, 2008),
including the Digit Span subtest (made up of three increasingly
difficult tasks: digit span forwards, backwards, and sequencing)
and the Arithmetic subtest (requiring to perform mental arith-
metic problems): taken together, performance at these tasks
provides the Working Memory Index (WMI), a global measure of
the ability to attend to information presented verbally, manipulate
it in short- term memory, and then formulate a response. The
tests were administered according to the standard procedure
reported in the WAIS- IV manual.

2. Stroop Colour and Word Test (Stroop, 1935): here we adopted a
computerised version of the task developed on the Open Sesame
software (version 3.3.8). The stimuli consisted of the words “red,”
“green,” “yellow” and “blue” presented at the centre of a black
computer screen in one of the four colours. The colour of the
word displayed corresponded to its meaning in 50% of the trials
(congruent condition), whereas in the remaining 50% of the tri-
als word colour and meaning were different (incongruent condi-
tion). Subjects had to indicate, as soon as possible, the colour of
the text by pressing a key on the keyboard corresponding to the
effective colour of the text. Subjects performed a short training
phase consisting of 24 trials in order to familiarise with the task
and afterwards they performed the task including 240 trials.

3. Source Monitoring task: a computerised Source Monitoring Task
(see Supporting Information) was included to evaluate the abil-
ity to discriminate between different sources of information. We
developed this task from Nienow and Docherty (2004), who origi-
nally evaluated internal source monitoring ability, that is the abil-
ity to discriminate between two internal sources of information.
According to the classification of source monitoring’s types pro-
posed by Johnson, Hashtroudi, and Lindsay (1993), we extended
the original task in order to test External Source Monitoring (i.e.
the ability to discriminate between two externally derived sources
of information) and Reality Monitoring ability (i.e. the ability to
discriminate between internal and external information sources).
Therefore, our task included three different subtests: Internal
Source Monitoring (I- SM), External Source Monitoring (E- SM) and
Reality Monitoring (RM- SM). Tasks presentation was counterbal-
anced between subjects.

2.5  |  Data analysis

Outcome measures of the DRM task were: number of false memo-
ries, i.e. total number of falsely recalled critical lure words; number
of veridical memories, corresponding to the total number of words

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6 of 12  |     MALLOGGI ET AL.

correctly recalled from the original word lists; number of intrusions,
representing the total number of recalled words not corresponding
to studied items or to the critical lure words. Only performance at
the two experimental lists (“pen” and “sleep” lists) were included in
data analysis, as the first and last lists (“flag” and “river” lists) were
used to control for primacy and recency effects (as in Baird, 2003).
Veridical memories were significantly more numerous for lists one
and four compared to lists two and three (lists one and four: mean
[SD] 11.64 [2.58] versus lists two and three: mean [SD] 9.98 [3.18];
Wilcoxon’s Z: 878.00; p < 0.001; ES:0.624), confirming the presence of primacy and recency effects.

Concerning executive functioning, the outcome measures were:
digit span scores, arithmetic scores and the WMI obtained from the
WAIS- IV subtests, as well as number of correct responses, number of
errors and response times (ms) for the Stroop task. Finally, Table 4 dis-
plays outcome variables considered for the source monitoring task.

Due to non- normal distribution of the data, we employed non-
parametric statistics. Cardinal variables were compared between the
IN and GS groups through the Mann– Whitney U test. Within- subject
comparisons were performed through the Wilcoxon signed- rank test.
Finally, Spearman and point- biserial correlation analysis were per-
formed to test the association memory performance, cognitive testing,
and source monitoring ability in the whole sample. Spearman correla-
tion was also performed to assess associations between sleep features
of the night before the DRM session and DRM performance in the
whole sample. The statistical significance level was set at p ≤ 0.05.

To test the interaction between groups and stimulus type, we
analysed the data with a mixed model logistic regression using the
statistical software R (version 4.0.3) and the package “lme4”. In this

analysis, we considered the total number of false memories as depen-
dent variable, the group (GS Group and IN Group) as fixed effect. The
random effects were the type of list and participant unique identifier.

We also performed a mediation analysis (using PROCESS macro;
SPSS version 27; Hayes, 2018) to test the role of source monitoring
ability as mediator of the relationship between sleep quality (i.e. IN
Group and GS Group) and the total number of false memories pro-
duced. We considered “Group” as independent variable and the total
number of false memories as dependent variable. The considered
mediator was the source monitoring ability, calculated by summing
up all the correct responses to the three source monitoring subtests
(i.e. I- SM, E- SM, and RM- SM). We calculated the indirect effect of
“Group” on false memories production, through source monitor-
ing ability, quantified as the product of the ordinary least squares
(OLS) regression coefficient estimating source monitoring ability
from “Group” and the OLS regression coefficient estimating false
memories production from source monitoring ability controlling for
“Group”. A bootstrapping procedure (with 5,000 bootstrap samples)
to estimate 95% confidence intervals (CIs) was used. According to
Preacher and Hayes (2008), a 95% CI that does not include zero pro-
vides evidence of a significant indirect effect.

An a priori power analysis was conducted. Taking into account
the sample size of the study and an α level of 0.05, a power analysis
based on Mann– Whitney U test testified that we were able to detect
an effect size equal to p = 0.717 (i.e. P represents the effect size
index (Trumble, Ferrer, Bay, & Mollan, 2020), in particular, P(X

TA B L E 4 Outcome variables of the source monitoring task

Source Monitoring task

Subtest Variable Description

I- SM I – correct The number of words correctly attributed to the internal sources of
information

I – Index 1 The proportion of words correctly identified as “said” out of the total
number of words correctly recognised as “old”

I – Index 2 The proportion of words correctly identified as “thought” out of the
total number of words correctly recognised as “old”

E- SM E – correct The number of words correctly attributed to the external sources of
information

E – Index 1 The proportion of words correctly identified as from “man” source
out of the total number of words correctly recognised as “old”

E – Index 2 The proportion of words correctly identified as from “women” source
out of the total number of words correctly recognised as “old”

RM- SM RM – correct The number of words that were correctly attributed to the internal
and the external sources of information

RM – Index 1 The proportion of words correctly identified as from internal source
out of the total number of words correctly recognised as “old”

RM – Index 2 The proportion of words correctly identified as from external source
out of the total number of words correctly recognised as “old”

E- SM, external source monitoring subtask; I- SM, internal source monitoring subtask; RM- SM, reality monitoring subtask.

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    |  7 of 12MALLOGGI ET AL.

3  |  RESULTS

3.1  |  False memories task

The IN Group globally produced more false memories (U = 247.00;
p = 0.04; ES = −0.27) than the GS Group (Figure 1). No differences
emerged between groups in the total number of veridical memo-
ries (mean [SD] IN Group 9.44 [3.33] versus GS Group 10.36 [2.93];
U = 284.00, p = 0.24) or in the number of intrusions (mean [SD] IN
Group 1.24 [1.09] versus GS Group 1.18 [1.02]; U = 340.50, p = 0.86).

Moreover, the IN Group generated more false memories
(U = 254.00; p = 0.04; ES = −0.28; Figure 2) and less veridical memo-
ries (U = 242.500; p = 0.05; ES = −0.27; Figure 3) at the sleep- related
list compared to the GS Group. Instead, the two groups did not dif-
fer neither in the number of false memories (mean [SD] IN Group
0.52 [0.51] versus GS Group 0.36 [0.48]; U = 239.00, p = 0.24) nor of
veridical memories (mean [SD] IN Group 5.52 [2.48] versus GS Group
5.50 [1.67]; U = 349.5, p = 0.99) at the neutral list.

As for within- subjects comparisons, the IN Group produced less
veridical memories for the sleep- related list compared to the neutral
list (Z = −2.587, p = 0.01; ES = −0.52; Figure 3), while no differences
between lists emerged in the number of false memories (Z = −0.378,
p = 0.71; Figure 2). The GS Group did not show differences in the
number of false memories (Z = −0.471, p = 0.63; Figure 2) or veridi-
cal memories (Z = −1.81, p = 0.10; Figure 3).

As for the linear regression model, we observed a significant
main effect of Group (F1,51 = 5.00, p = 0.03), whereas no significant
main effect of list type (F1,51 = 0.04, p = 0.84) nor interaction effect
(F1,51 = 0.37, p = 0.55) emerged.

3.2  |  Executive functioning tasks

No between- groups differences emerged at the working memory
and Stroop tasks (Table 5).

As for source monitoring ability, the IN Group had lower scores
in Index 1 at the RM- SM subtest compared to the GS Group
(ES = −0.29; Table 6), suggesting difficulties in correctly discrimi-
nating between internal and external sources of information. There
were no other between- groups differences.

The number of false recalls at the sleep- related list showed a
negative correlation with the number of correct responses to the
Stroop task (r = −0.355, p = 0.03) and a positive correlation with the
number of errors (r = 0.355, p = 0.03), while the number of veridi-
cal recalls for the same list positively correlates with the digit span
score (r = 0.376, p = 0.02) and the WMI of the WAIS- IV (r = 0.344,
p = 0.03). Also, the total number of veridical memories showed
a positive correlation with the WMI of the WAIS- IV (r = 0.352,
p = 0.03) and a negative correlation with the total number of er-
rors at the I- SM task (r = −0.322, p = 0.05). As for the relationship
between sleep measures of the night preceding the DRM session
and subsequent DRM performance, we observed a positive correla-
tion between the total number of false memories and the number of

night awakenings (r = 0.267, p = 0.05), whereas the total number of
veridical memories showed a trend to a significant positive correla-
tion with sleep duration (r = 0.266, p = 0.09). No other significant
correlations emerged.

The results of the mediation analysis revealed a non- significant
indirect effect of sleep quality on false memories production
through source monitoring ability (point estimate = 0.04, 95% CI
−0.085, 0.086).

4  |  DISCUSSION

In the present study we investigated false memories production
in individuals with insomnia and in good sleepers, assuming that
poor sleep quality and its cognitive consequences (see for a review
Fortier- Brochu et al., 2012) can render the former more prone to this
phenomenon.

As a main result, we observed that the IN Group globally pro-
duced more false memories compared to the GS Group, thus sup-
porting an association between sleep quality and false memories
production. In light of the literature on cognitive functioning in
insomnia disorder, this result is of particular interest. According to
the Activation- Monitoring theory (Roediger & McDermott, 1995;
Roediger, Watson, McDermott, & Gallo, 2001), during the retrieval
phase participants generally rely on a source monitoring process to
separate items that were studied from those that were not: in this
phase, frontally mediated executive functions are essential to ensure
efficient source monitoring and memory accuracy (Johnson, Raye,
Mitchell, & Ankudowich, 2012). In this regard, it has been observed
that false memories production is increased in healthy subjects after
sleep deprivation (Diekelmann et al., 2008, 2010), a procedure that
strongly affects prefrontal functioning (Durmer & Dinges, 2005).
In subjects with insomnia, previous studies documented diurnal
impairment in the same cognitive functions that may help to reject
false memories and ensure efficient memory recall, i.e. retention and
manipulation of information in working memory, inhibitory control,
and cognitive flexibility (Fortier- Brochu et al., 2012).

In our present study, we did not observe significant between-
groups differences in most executive tasks. However, it would be
hazardous to rule out the presence of executive impairments in
insomnia. It might be that the changes in cognitive performance
reported in the present population are of a subtler and more situa-
tional kind (Fortier- Brochu et al., 2012) and therefore went partially
undetected in the classical neuropsychological tasks adopted here.
Moreover, the suggested relationship between executive function-
ing and performance at the DRM paradigm (see e.g. Leding, 2012;
Peters et al., 2007) seems to be supported by the correlational analy-
sis. In fact, we observed that the number of false recalls is negatively
associated with accuracy at the Stroop task, and, conversely, that
the number of veridical memories correlates both positively with the
WMI and negatively with accuracy at the source monitoring task.

Additionally, an interesting result comes from the RM- SM sub-
test of the source monitoring task, at which the IN Group were less

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8 of 12  |     MALLOGGI ET AL.

accurate than the GS Group. Importantly, this bias was limited to
the RM- SM subtest, which requires participants to discriminate
between internally and externally generated stimuli, i.e. the same
ability required by the DRM task (while it did not extend to the abil-
ity to discriminate between two internal or two external sources).
Together with our observation of higher false recall in the IN Group,
this finding lends support to the Source Monitoring Framework
(SMF) in the explanation of false memories formation (Mitchell &
Johnson, 2000) and to the hypothesis that the protective role of ex-
ecutive functioning against false memory is weakened in subjects
with insomnia. In fact, according to the SMF, false memories arise

from an error of commission, that is when thoughts or images com-
ing from one source (e.g. an external one) are erroneously attributed
to another one (e.g. an internal one; Mitchell & Johnson, 2000). The
ability to correctly discriminate between two sources of information
is linked to the efficiency of executive functioning and especially
of memory retrieval processes (Johnson et al., 2012): the latter are
strongly modulated by prefrontal functioning and are affected by
acute (Durmer & Dinges, 2005; Frenda & Fenn, 2016; Mitchell &
Johnson, 2000) and chronic sleep loss, as in the case of individuals
with insomnia (Fortier- Brochu et al., 2012). Therefore, in line with
the SMF, we may explain our present results by assuming that the IN
Group produced more numerous false memories than the GS Group
because they are more susceptible to errors of commission as a con-
sequence of their chronic sleep loss.

The data described so far should still be cautiously interpreted
for the methodological limitation represented by the limited sample
size, possibly accounting for the low magnitude of the finding and the
negative results of our mediation analysis. However, taken overall,
they encourage to thoroughly consider and further experimentally
explore the hypothesis that the efficiency of executive functions,
including the crucial source monitoring ability, promotes accurate
retrieval and prevents false memories formation (Diekelmann et al.,
2008; Peters et al., 2007).

Another interesting finding concerns the influence of stimulus
type on DRM performance in the IN Group. In accordance with lit-
erature on the attentional bias for sleep- related stimuli in individuals
with insomnia (Giganti et al., 2017; Harris et al., 2015), we observed
greater false recall at the “sleep” list in the IN Group compared to
the GS Group. Indeed, it is known that individuals with insomnia
preferentially focus their attention on sleep- related items, consid-
ering them more salient and “threatening” than neutral ones (Espie
et al., 2006; Harvey, 2002). This phenomenon has been previously

F I G U R E 1 Comparison between the insomnia group (IN Group)
and good sleep group (GS Group) in the total number of false
memories. *p ≤ 0.05. Error bars represent standard deviations
[Colour figure can be viewed at wileyonlinelibrary.com]

F I G U R E 2 Comparison between the
insomnia group (IN Group) and good
sleep group (GS Group) in the number of
false memories for neutral list and sleep-
related list. *p ≤ 0.05. Error bars represent
standard deviations [Colour figure can be
viewed at wileyonlinelibrary.com]

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observed through specific cognitive tests (see e.g. Giganti et al., 2017;
MacMahon et al., 2006), but had not yet been investigated in a task
based on strong semantic associations, such as the DRM paradigm.
Previous studies on the DRM task show that, relative to neutral word
lists, arousing and negatively valenced lists can promote stronger as-
sociative connections between their items, so that the non- presented
lures undergo greater activation and their false recall is facilitated at

subsequent recovery (Howe, Wimmer, Gagnon, & Plumpton, 2009;
Otgaar, Howe, Brackmann, & Smeets, 2016). Therefore, we can ex-
plain our present result by assuming that, for our IN Group, items
of the “sleep” list were more arousing and negatively valenced com-
pared to the neutral list. Although in our study we did not directly
ascertain whether the IN Group actually judged the sleep- related
words as more negative and arousing than neutral ones, it has been

F I G U R E 3 Number of veridical
memories for neutral list and sleep- related
list in the insomnia group (IN Group) and
good sleep group (GS Group). *p ≤ 0.05;
**p ≤ 0.01. Error bars represent standard
deviations [Colour figure can be viewed at
wileyonlinelibrary.com]

TA B L E 5 Comparison between the insomnia group (IN Group) and good sleep group (GS Group) in Stroop task and Wechsler Adult
Intelligence Scale, fourth edition (WAIS- IV) performance

Task Variable IN Group, mean (SD) GS Group, mean (SD) U p

Stroop Stroop – correct responses 230.35 (29.54) 232.20 (25.52) 306.00 0.84

Stroop – errors 9.65 (29.53) 7.80 (25.52) 363.00 0.85

Stroop – response times 872.78 (163.26) 851.07 (177.47) 364.00 0.70

WAIS Digit span subtest 9.71 (3.02) 9.57 (2.38) 322.50 0.87

Arithmetic subtest 5.00 (3.06) 5.29 (3.28) 324.00 0.78

Working Memory Index 84.82 (13.72) 85.38 (13.09) 325.50 0.90

TA B L E 6 Comparison between the insomnia group (IN Group) and good sleep group (GS Group) in the source monitoring task

Subtest Variables IN Group, mean (SD) GS Group, mean (SD) U p

I- SM I – correct 18.64 (3.84) 19.19 (2.73) 166.00 0.61

I – Index 1 56.18 (5.87) 55.87 (8.07) 177.00 0.83

I – Index 2 43.82 (5.87) 44.13 (8.07) 177.00 0.82

E- SM E – correct 18.11 (3.99) 18.38 (2.94) 169.50 0.82

E – Index 1 55.10 (14.23) 56.14 (13.56) 167.00 0.84

E – Index 2 44.91 (14.24) 43.85 (13.56) 167.00 0.88

RM- SM RM – correct 20.52 (2.34) 19.00 (3.11) 125.50 0.43

RM – Index 1 47.33 (6.22) 54.16 (13.52) 107.50 0.03

RM – Index 2 51.28 (6.34) 45.65 (13.46) 114.50 0.21

E- SM, external source monitoring subtask; I- SM, internal source monitoring subtask; RM- SM, reality monitoring subtask.

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10 of 12  |     MALLOGGI ET AL.

previously shown that emotional valence and arousing capacity of
sleep- related stimuli strongly differ between subjects with insomnia
and good sleepers (Baglioni et al., 2010; Zhou et al., 2018).

Here again, given that the regression model did not show a sig-
nificant interaction between group and stimulus type, we should
take into account, beyond the small sample size, two further limits of
our present study: (a) we did not include a specific measure of atten-
tional bias, which would have enabled us to exclude that between-
groups differences are due to factors other than stimulus type; (b)
we could not analyse fine- grained differences in characteristics of
our DRM lists, such as semantic relatedness and forward– backward
associative strength between words, that might have played a role.

Surprisingly, we observed that veridical recall at the “sleep” list
was impaired in the IN Group, both relative to their own perfor-
mance at the neutral list and to the GS Group. This result suggests
that, in the IN Group, the attentional bias for the sleep- related list
has different consequences on false and veridical memories, with an
enhancement of false recall paralleling an impoverished veridical re-
call. Assuming in this group a higher activation driven by the salience
of the sleep- list, a better veridical recall (relative both to the neu-
tral list and to the GS Group) for this list could be expected. In fact,
previous studies showed that, in subjects with insomnia, the atten-
tional bias generally enhances performance on sleep- related stimuli
by locating greater attentional resources on them (see e.g. Giganti
et al., 2017; MacMahon et al., 2006). Moreover, studies adopting
the DRM paradigm on healthy subjects showed that salient stim-
uli generally enhance both false memories and veridical recollection
of stimuli (Baird, 2003; Castel et al., 2007). However, some authors
pointed out that certain stimuli not only promote false memories
production but also, in parallel, reduce veridical retrieval (Brainerd,
Holliday, Reyna, Yang, & Toglia, 2010). To this regard, adopting the
DRM paradigm, Brainerd et al. (2010) observed that stimuli with
negative valence generally increase false memories production but,
at the same time, can also suppress true memory recollection, ex-
plaining this result in light of the Fuzzy- Trace Theory (Brainerd &
Reyna, 2002). According to this theory, subjects simultaneously en-
code two independent traces for each word, respectively the “ver-
batim trace” (i.e. the trace related to the contextual features of a
word and especially linked to veridical memory, corresponding in the
DRM paradigm to the “studied words”) and the “gist” or “fuzzy” trace
(i.e. the trace representing the meaning of an item, preferentially
linked to false memories production). The presentation of arousing
and negatively valenced stimuli generally leads to strong gist traces
but, at the same time, could also interfere with simultaneous pro-
cessing of verbatim traces, causing lower subsequent hit rates for
negative targets (Brainerd et al., 2010). In our present study, the
sleep- related word list might have performed in this way. In other
words, supposing a high activation driven by the sleep- related list
in our IN Group, the triggering of the gist trace “sleep” in this group
could have: on one hand, promoted false recall at the sleep- related
list; on the other hand, interfered with the processing of verbatim
sleep- related traces and consequently impacted the veridical recall
of words semantically associated to the gist trace.

Concerning the neutral word list, we did not observe between-
groups differences either in the number of false or veridical memories.
This result seems to suggest that, in absence of interference such as
that linked to sleep- related stimuli, individuals with insomnia have an
efficient declarative memory system for words that are semantically
related. In fact, as further evidence of this cognitive efficiency, we did
not detect between- groups differences in the number of intrusions
(i.e. words not belonging to the original word lists and also not seman-
tically related to the critical lure words). It could be the case that the
well- documented declarative memory deficits in people with insom-
nia (Fortier- Brochu et al., 2012) specifically emerge in tasks assessing
memory retrieval of semantically unrelated words. In other words, the
semantic association between stimuli, which generally facilitates their
recall (Aka, Phan, & Kahana, 2020; Silberman, Miikkulainen, & Bentin,
2005), would allow sleep- impaired individuals to achieve at the DRM
task the same performance as good sleepers.

Because of the limited statistical power and the small effect size,
our present results need to be carefully interpreted and require fur-
ther replications in larger samples. Indeed, as pointed out by Fortier-
Brochu et al. (2012), small sample size and low statistical power are a
common issue in studies comparing cognitive performance between
people with insomnia and good sleepers and may prevent the de-
tection of small group differences. Nevertheless, our present results
add to the previous literature on the attentional bias in subjects with
insomnia and open to new research question.

In conclusion, our present data show that individuals with in-
somnia symptoms produce more false memories than good sleepers
and point to a relevant role of the attentional bias for sleep- related
stimuli in the DRM task in this clinical sample. Although we cannot
assert that the increase in false memories production in people with
insomnia is due to a widespread impairment of executive function-
ing, our present results highlight in this population a notable bias in
source monitoring ability that could have contributed to their false
memories production.

ACKNOWLEDG EMENTS
This study has been partially supported by the “V:ALERE 2019” pro-
ject of the University of Campania “L. Vanvitelli”. We thank Dr Monica
Annunziata for her precious help in data collection. Open Access
Funding provided by Universita degli Studi di Firenze within the CRUI-
CARE Agreement. [Correction added on 30 May 2022, after first on-
line publication: CRUI funding statement has been added.]

CONFLIC T OF INTERE S T
The authors declare no conflicts of interest, no personal financial
support and involvement with an organisation with financial interest
in the subject matter of the paper.

AUTHOR CONTRIBUTIONS
All authors contributed in a meaningful way to this manuscript.
Conceptualisation of the research, SM, FC, SR, GF, and FG; meth-
odology, SM, FC, GG, GF, and F.G; formal analysis, SM, ODR, GG,
and FG; investigation, SM and ODR; data curation, SM, GG, and FG;

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    |  11 of 12MALLOGGI ET AL.

writing – original draft preparation, SM and FG; writing – review and
editing, SM, FC, and FG; supervision, FC, GF, and FG; project ad-
ministration, GF and FG. All authors have read and agreed to the
published version of the manuscript.

DATA AVAIL ABILIT Y S TATEMENT
The data that support the findings of this study are available from
the corresponding author upon reasonable request.

ORCID
Serena Malloggi https://orcid.org/0000-0003-1813-8916
Francesca Conte https://orcid.org/0000-0002-5429-5831
Oreste De Rosa https://orcid.org/0000-0001-6964-5024
Stefania Righi https://orcid.org/0000-0001-7852-2448
Giorgio Gronchi https://orcid.org/0000-0003-0543-4900
Gianluca Ficca https://orcid.org/0000-0001-9519-4351
Fiorenza Giganti https://orcid.org/0000-0002-9362-5258

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https://doi.org/10.1097/01.nmd.0000142018.73263.15

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https://doi.org/10.1016/j.smrv.2009.06.001

https://doi.org/10.1111/j.0956-7976.2005.00797.x

https://doi.org/10.1111/j.0956-7976.2005.00797.x

https://doi.org/10.1111/j.1365-2869.2008.00641.x

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https://doi.org/10.1111/jsr.13527

https://doi.org/10.1111/jsr.13527

• False memories formation is increased in individuals with insomnia

Summary

1|INTRODUCTION

2|METHODS

2.1|Participants and procedure

2.2|Screening instruments

2.3|False memories task

2.4|Executive functioning tasks

2.5|Data analysis

3|RESULTS

3.1|False memories task

3.2|Executive functioning tasks

4|DISCUSSION

ACKNOWLEDGEMENTS

CONFLICT OF INTEREST

AUTHOR CONTRIBUTIONS

DATA AVAILABILITY STATEMENT

REFERENCES

E-mail address: fusi@cns.unibe.ch (S. Fusi).

Neurocomputing 38}40 (2001) 1223}1228

Long term memory:
Encoding and storing strategies of the brain

Stefano Fusi
Institute of Physiology, University of Bern, Bu( hlplatz 5, 3012 Bern, Switzerland

Abstract

Plastic material devices, either arti”cial or biological, should be capable of rapidly modifying
their internal state to acquire information and, at the same time, preserve it for long periods (the
stability}plasticity dilemma). Here we compare, in a simple and intuitive way, memory stability
against noise of two di!erent strategies based, respectively, on fully analog devices that
accumulate linearly small changes and on systems with a limited number of stable states and
threshold mechanisms. We show that the discrete systems are more stable, even with short
inherent time constants, and can easily exploit the noise in the input to control the learning rate.
We “nally demonstrate the strategy by discussing a model of a biologically plausible spike-
driven synapse. � 2001 Elsevier Science B.V. All rights reserved.

Keywords: Synaptic plasticity; Long term memory; Learning

1. Introduction

Material (arti”cial or biological) learning devices, like the synapses, have the
capability of changing their internal states in order to acquire (learn) and store
(memorize) information about the statistics of the incoming #ux of stimulations. In
a realistic situation, the stimulations carrying relevant information are separated
by long time intervals of noisy input which tends to erase the memory of the
previously acquired information.Moreover the interference of novel stimulations with
already acquired older &memories’ may give rise to memory loss (e.g. the oldest
stimulations are forgotten to make room for the new ones). This is also known as the

0925-2312/01/$ – see front matter � 2001 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 5 – 2 3 1 2 ( 0 1 ) 0 0 5 7 1 – 9

stability}plasticity dilemma: the memory should be stable against irrelevant inputs
(e.g. noise) for long periods and, at the same time, the internal state should be rapidly
modi”ed to acquire the information conveyed by the relevant inputs. This dilemm

a

becomes particularly arduous when dealing with material memory devices that do not
allow arbitrarily large time constants or parameters “ne tuning, especially if the
devices are small (e.g. it is reasonable to assume that permanent changes can not be
arbitrarily small).
Here we show one possible encoding and storing strategy that solves this dilemma

and we exemplify it by discussing a model of a spike-driven learning synapse. The
strategy is based on the assumption that information to be coded is redundant: e.g. for
the synapses this means that many cells on the dendritic tree carry similar informa-
tion.We compare two possible scenarios: in the “rst each synapse is described in terms
of one continuous internal variable x. In the absence of any stimulation, the value
encoded by x is preserved forever. In the second, the synapse is discrete on long time
scales: it has only a limited number of attracting stable states: when x drifts away from
one of them, a recalling force drives it back to the closest stable state. To make
a change permanent, the internal variable should cross some threshold, to be then
attracted towards a di!erent stable state. Let K be the number of stable states and �x
the minimal distance between two stable states.

2. Preserving information: The stability problem

We now consider the current generated by the synaptic inputs as the relevant
variable. We assume that it is approximately the linear sum of many input neuronal
activities a

�
multiplied by the corresponding weights J

�
, which, in turn, depend on the

internal state of the synapses. Let

I
�

be the current induced by N neurons that encode

the same information, i.e. that are activated in the same way by a generic stimulus
(a

�
“a for i”1,2,N):

I
�

”

1

N

�
�
���

J
�
a
�
”

a

N

�
�
���

J
�
.

If we start from the fully analog synaptic values and we clamp them to the closest

stable states (see Fig. 1), the error on I
�
goes as &1/(K�N). If N is large enough (the

code is redundant), the error becomes negligible and there is no relevant loss of
information, which would be the only disadvantage of the discrete code. This is
a known property of some neural networks (see e.g. [6]).
However, memory preservation is much more stable in the case of discrete synapses

since the e!ects of noise do not accumulate. Let �t be the typical `responsea time of the
synaptic device, i.e. the time interval during which any change of an internal variable
is established: the noise induces small jumps �x with probability p, either upwards or
downwards, once every �t. The ratio p/�t can also be seen as the rate of events that can
induce permanent changes (e.g. the spikes). Let � be the time constant of the recalling
force: no matter how far x gets from one stable state, in a time of the order of �, it is

1224 S. Fusi / Neurocomputing 38}40 (2001) 1223}1228

Fig. 1. Clipping synaptic e$cacies: passing from fully analog synapses (left) to three-state synaptic e$cacies
(right) does not degrade much of the memory. The input neurons (below) are arranged in such a way that
the “rst N neurons are driven by a generic stimulus to the same activity level. These neurons carry the same
information (redundancy) for that speci”c stimulus. The e$cacies are di!erent because other uncorrelated
stimuli, activating di!erent subsets of neurons, had been previously encoded. When clipped to the closest
stable state, the synapses are pushed up and down and the “nal `errora on the a!erent current I

�
, generated

by N neurons, is equivalent to a noise whose amplitude scales as 1/�N.

driven back to the closest stable state. For the fully analog synapse, after time ¹, the

mean displacement is of the order of �x�p¹/�t. Hence, to have an error of �x, one
has to wait a time of the order of:

¹��&�t�
�x

�x�
�
p��.

If the internal variable x hits one of the boundaries, this time is even shorter [4]. For
the discrete synapse, the same error �x is produced when a #uctuation drives the
internal variable across the threshold. This happens with a probability &(p�/�t)� per
� where h”�/�x is the number of jumps required to reach �. Hence

¹��
&�t

�
�t�

p�
�t�

��
, (1)

which can be much longer than the time of the fully analog synapse, especially if p is
small. It can be so long, that x practically never hits the boundaries (see Section 4). The
best case is when h is maximal, i.e. when the synapse is binary. The same behavior
could be obtained in the analog case by adding an extra device that triggers perma-
nent modi”cations only if some threshold is crossed. However, there is accumulating
experimental evidence that the single synaptic contacts are actually binary on long
time scales [5].

3. Acquiring information: The plasticity problem

It was rather intuitive and well known that discreteness can increase stability
without necessarily degrading memory performance. What was less clear is whether
this is still true in case of on-line learning, when discrete synapses are updated after
every stimulus presentation. Actually discreteness can be advantageous also in this

S. Fusi / Neurocomputing 38}40 (2001) 1223}1228 1225

Fig. 2. Updating synaptic e$cacies. The scheme is described in Fig. 1. Upon the presentation of a generic
stimulus, the analog synapses (left) are potentiated by �”�x/4. Since theN synapses see the same pre- and
post-synaptic activity they are all updated in the same way. The same change in I

�
can be obtained in the

discrete case by modifying only a fourth of the N synapses (synapse �2 in the “gure). This can be obtained
with a stochastic selection mechanism that updates each synapse with probability q”1/4. Interestingly the
presentation of a generic pattern interferes with the memory of other uncorrelated patterns in the same way
in the two scenarios. Indeed, if f is the fraction of neurons activated by a di!erent stimulus, the “nal change
in its current would be fN� in the analog case and fqN�x in the discrete case. For a more general analytical
study see [1].

case. Since the code is redundant, there is no need to modify all the synapses. If the
fraction of synapses that are changed following each stimulation is small (slow
learning), it is possible to better redistribute the synaptic &memory’ resources among
the di!erent patterns of stimulation and actually recover the optimal storage capacity
even with binary synapses [1]. Slow learning is usually di$cult because it is rather
unlikely that the minimal change � inducible by the input is arbitrarily small. After
M repetitions of the same signal, the minimal change of I

�
would be M�. In the

discrete case, the noise superposed to the stimulations can turn in our favor by
providing a triggering signal which selects in a local and unbiased way a small fraction
of synapses to be changed. With the threshold mechanism of the discrete case, the
input, at parity of signal, can induce or not a permanent change, i.e. a transition to
a di!erent stable state. In this case the minimal change in Iwould beMq�x, where q is
the transition probability for each synapse. q�x can be much smaller than � and the
average number of synapses changed after each repetition can be even(1 (see Fig. 2).
This scheme has the very attractive feature that it transfers part of the updating
process outside the device (e.g. embedded in the input): q is not necessarily related to
the intrinsic dynamics of the system. This can be a much better strategy, especially for
small devices with short time constants.

4. Spike-driven synaptic plasticity

To demonstrate how the load of generating low probability events can be transfer-
red outside the device, we discuss a model of a bistable (K”2) spike-driven learning
synapse which has been recently introduced [3]. The transitions between the two
states are activity dependent and stochastic, even without any intrinsic noise source in
the synaptic device. The synapse exploits the #uctuations in the inter-spike intervals,

1226 S. Fusi / Neurocomputing 38}40 (2001) 1223}1228

Fig. 3. Simulation of stochastic LTP. Pre- and post-synaptic neurons have the same mean rate and the
synapse starts from the same initial value. At parity of activity (signal), the “nal state is di!erent in the two
cases.

Fig. 4. Contour plots of LTP and LTD probabilities (q) on log scale vs pre- and post-synaptic neuron rates
for a 500 ms stimulation. LTP occurs when pre- and post-synaptic rates are both high. Around the white
plateau, P

���
drops sharply and becomes negligible for spontaneous rates. The strong non-linearity allows

to discriminate easily between relevant signals and background noise.

which are the results of the collective dynamics of the network. This noise is always
superposed to the signal (pre- and post-synaptic mean frequencies) during the stimula-
tion and is di!erent from synapse to synapse. Each pre-synaptic spike drives the
internal state x either up or down depending on whether the post-synaptic depolariz-
ation is above or below the threhsold �

�
. LTP/LTD might occur or not at parity of

mean pre-synaptic and post-synaptic activities (see Fig. 3). In this case p (see Eq. (1)) is
the probability of coincidence of two events (e.g. a pre-synaptic spike and high
depolarization) and hence can be very small. In Fig. 4 we show that the stochastic
transitions between stable states are easily manipulable. In the presence of noise (low,
spontaneous activity), the time to wait for a transition can be of the order of years,
even if the longest time constant � is of the order of 100 ms, whereas under stimulation
(higher frequencies) the transition probabilities are easily controllable in the range

S. Fusi / Neurocomputing 38}40 (2001) 1223}1228 1227

10��}10��, as expected from Eq. (1). Extensive simulations of the learning process in
networks of integrate-and-“re neurons connected by the proposed synapse are pre-
sented in [2].
We believe that this strategy based on the combination of discreteness and external

stochasticity is a good general strategy for storing variables on long time scales and it
is likely to underlie the basic mechanisms of many other biological small systems.
Moreover this analysis shows that synaptic models in which single events (e.g. single
spikes) modify permanently the synaptic e$cacy can be hardly used as long term
memory devices since the information acquired during the stimulation would be
erased in a short time by the spontaneous activity.

References

[1] D.J. Amit, S. Fusi, Learning in neural networks with material synapses, Neural Comput. 6 (1994)
957}982.

[2] P. Del Giudice, M. Mattia, Long and short term synaptic plasticity and the formation of working
memory: a case study, Neurocomputing 38}40 (2001) 1175}1180, this issue.

[3] S. Fusi, M. Annunziato, D. Badoni, A. Salamon, D.J. Amit, Spike-driven synaptic plasticity: theory,
simulation, VLSI implementation, Neural Comput. 12 (2000) 2227}2258.

[4] G. Parisi, A memory which forgets, J. Phys. A 19 (1986) L617.
[5] C.C.H. Petersen, R.C. Malenka, R.A. Nicoll, J.J. Hop”eld, All-or-none potentiation at CA3-CA1

synapses, Proc.Natl.Acad.Sci. 95 (1998) 4732.
[6] H. Sompolinsky, The theory of neural networks: the Hebb rule and beyond, in: L. van Hemmen, I.

Morgenstern (Eds.), Heidelberg Colloquium on Glassy Dynamics, Springer, 1987.

Stefano Fusi was born in 1968 in Florence, Italy. He received his master degree in
physics from the university of Roma in 1992. He had been working as a researcher
in the National Institute of Nuclear Physics (INFN, Roma) from 1993 to 1999 and
received a Ph.D. in physics from the HebrewUniversity of Jerusalem in 1999. He is
currently working in the Institute of Physiology of Bern. His research interests
include long-term synaptic plasticity, in vivo experiments on behaving monkeys,
neuromorphic VLSI hardware and analytical studies of networks of spiking
neurons.

1228 S. Fusi / Neurocomputing 38}40 (2001) 1223}1228

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