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Dissociative amnesia

A few months ago, Cn2r published a dossier on the links between memory and trauma, looking at how traumatic memories can be altered, fragmented or even erased. Following on from this, today we return to an equally intriguing phenomenon: dissociative amnesia. Formerly known as psychogenic amnesia, and then considered a neurotic symptom linked to repression, it is now defined as an inability to remember important autobiographical information that may be linked to trauma or stress. Classified as a specific dissociative disorder in manuals such as DSM-5 and ICD-11, it can also appear as a symptom in other pathologies, notably post-traumatic stress disorder (PTSD).

Even today, it remains the subject of lively debate within the scientific, legal and medical communities. Indeed, it was the focus of a webinar organized in 2022 by Cn2r, in collaboration with Olivier Dodier, to address its mechanisms, conceptual limits and implications. Its clinical and legal implications are major: how can we guarantee appropriate care for victims, while ensuring the reliability of testimony in cases of sexual violence? This dossier examines these questions by exploring dissociative amnesia from several angles, while highlighting the recent scientific controversies surrounding this disorder.

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Evolution of a concept

Dissociative amnesia has long been at the heart of debates in psychology and psychiatry. Over the centuries, its conceptualization has evolved, influenced not only by advances in psychology, but also by a better understanding of the underlying neurobiological mechanisms.

dissociative amnesia

The beginnings: medical recognition of amnesia

The concept of amnesia as a distinct disorder was formalized as early as the 18th century by physician and botanist François Boissier de Sauvages, who, in his "Nosologia Methodica" (1763), classified amnesia as an abolition or diminution of memory. He already distinguished physical causes from emotional origins, paving the way for a more nuanced understanding of the psychological processes that could explain forms of amnesia not associated with brain lesions.

The 19th century: the theoretical foundations of dissociation

The notion of dissociative amnesia began to take shape in the 19th century, thanks in particular to the work of Prof. Théodule Ribot and Prof. Jean-Martin Charcot. Ribot introduced his famous "law of regression" in 1881, postulating that memory loss follows a temporal order, primarily affecting recent, more fragile memories. Charcot, for his part, observed that emotional trauma could lead to a break in the continuity of consciousness and memory, an observation that prefigured future theories of dissociation.

Dr Pierre Janet: the birth of the modern concept

The real development of the modern concept of dissociative amnesia came with Dr. Pierre Janet, who in 1894 proposed the idea of dissociation as a psychic defense mechanism against trauma, while acknowledging the role of intense emotions and possible constitutional psychic weakness in its occurrence. According to Janet, dissociative amnesia is a psychological response in which certain memories become inaccessible to normal consciousness to protect the individual from trauma. His theories had a considerable influence on clinical understanding of dissociation, and continue to resonate in modern classifications, notably in the Diagnostic and Statistical Manual of Mental Disorders-5 (DSM-5). While his ideas on dissociation were widely disseminated in Anglo-Saxon countries, they initially aroused less enthusiasm in France, where Freudian theories on repression dominated the intellectual debate. It wasn't until the 1980s, with the evolution of mental disorder classifications and the introduction of dissociation-related concepts in the DSM, that Janet's perspectives regained a notable place in the French clinical field.

Freud and repression

At the turn of the 20th century, Freud and Breuer re-evaluated Janet's concepts of dissociation by introducing the idea of repression. Whereas Janet conceived of dissociation as a passive fragmentation of memory - a psychic inability to integrate certain traumatic memories into ordinary consciousness - Freud saw repression as a more dynamic defense mechanism, in which unbearable thoughts and memories are kept out of consciousness in order to preserve psychic equilibrium. In their studies on hysteria (1895), Freud and Breuer, while quoting Janet, enriched his conception of dissociation with a more active approach, in which the ego engages in a deliberate process of repression in the face of threatening psychic content. Where Janet described a dissociation marked by the automatic, involuntary splitting of memory, Freud and Breuer introduced a defensive psychic barrier that redirects and confines these elements to the unconscious, transforming the interpretation of dissociation into a more elaborate act of psychic protection.

Changes in classification

Over time, dissociative amnesia has been incorporated into official classifications, notably the DSM. Each new edition has brought further clarification. DSM-3 (1980) marked a milestone by introducing the notion of psychogenic amnesia under the term dissociation, a trend confirmed in DSM-4 (1994) and, more recently, in DSM-5 (2013). These successive revisions have helped to formalize and refine the definition of dissociative amnesia, specifying that it is a memory loss of non-neurological origin, often linked to traumatic or stressful events.

Clinical acceptance despite scientific criticism

While the concept of dissociative amnesia, particularly in its localized or selective forms, is still well established in clinical and forensic practice, the scientific evidence in support of it remains weak and often insufficient. These methodological shortcomings, highlighted in recent scientific publications, are compounded by ethical and deontological barriers to scientific progress.

According to psychology researcher Géraldine Tapia, ethical barriers represent a major challenge for dissociative amnesia research: "It is unthinkable to intentionally confront people with a traumatic event in order to study its memory repercussions."

This limitation makes it difficult to directly observe the phenomenon of dissociative amnesia in the laboratory, and research must therefore often rely on case studies or animal models to explore the underlying mechanisms Thus, dissociative amnesia today seems to lie in a grey area between marked clinical interest and questioned scientific legitimacy.

ZOOM

According to the DSM-5, dissociative amnesia manifests itself as "an inability to recall important autobiographical information, usually related to traumatic or stressful events, the extent of which exceeds that which could be attributed to simple forgetfulness". Memory recovery sometimes occurs spontaneously after several hours, when the individual moves away from the traumatic circumstances at the origin of the amnesia (DSM-5-TR).

This disorder affects retrograde episodic memory, and can affect periods ranging from a few hours to several decades. In the majority of cases, dissociative amnesia is disproportionate: individuals may lose access to large portions of their past, while retaining their ability to form new memories and perform everyday tasks. Some forget specific periods (such as a stressful relationship), while others may even forget their own identity.

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In addition, this amnesia can affect the recognition of familiar faces or objects, and in rare cases, lead to the loss of acquired skills. In some cases, dissociative amnesia can be associated with dissociative fugue, where the individual moves around without remembering their past or their identity.

Current description

Formerly known as "psychogenic amnesia" or "functional amnesia", dissociative amnesia is also known as traumatic amnesia. It manifests as incomplete or global autobiographical amnesia, to the extent that the individual may lose his or her identity and be found wandering far from home if accompanied by dissociative fugue. It appears in diagnostic manuals such as the DSM-5-TR and ICD-11, where it is classified as a dissociative disorder, and may also appear as a possible symptom of post-traumatic stress disorder (PTSD).

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The term dissociative replaced psychogenic in the DSM-4, deemed too vague, although it is still used in some classifications, such as ICD-10. Dissociation, as defined by Dr Pierre Janet in 1893, refers to a "narrowing of the field of consciousness" linked to an intense emotional or traumatic shock, a concept often taken up in the modern understanding of dissociative amnesia (Janet, cited by Thomas-Anterion, 2017).

On the other hand, the term "functional" is sometimes used to characterize this type of amnesia, particularly in clinical settings. This term indicates that brain structures are intact, but their function is temporarily impaired. It underlines the reversible nature of dissociative amnesia, with no observable brain damage.

Facts and figures

A study published in The Lancet Psychiatry estimates the prevalence of dissociative amnesia at between 0.2 and 7.3% with a sex ratio of 1:1, mainly affecting 20-40 year-olds (Staniloiu & Markowitsch, 2014).

The different shapes

Localized: forgetting events that occurred during a specific period.
Selective: forgetfulness of certain aspects of a traumatic event.
Generalized: complete loss of memory concerning identity and life history.
Systematized: forgetfulness of information relating to a specific category, such as specific people or events.
Continuous: inability to remember new events from a certain point onwards, with each new experience immediately forgotten.

The terms

Psychogenic amnesia: a broader term than dissociative amnesia, linking amnesia to a wider range of psychological mechanisms (dissociation, suppression, cognitive avoidance, motivated forgetting, etc.).
Functional amnesia: memory disorders that cannot be attributed to organic or psychological causes.
Mnestic block syndrome: retrograde memory block caused by psychological effects such as severe stress or psychological trauma.
Hysterical Amnesia: obsolete term used since the late 19th century to describe a stress-related disorder resulting in extreme emotional arousal and memory loss.

Theoretical models

Since the 1990s, several theoretical models have attempted to explain the mechanisms of dissociative amnesia, particularly in the context of post-traumatic stress disorder (PTSD). In a recent study, Tapia et al. review the main theoretical models, based on neurobiological and behavioral data from human and animal research (for more details, see below). The authors point out that there is currently no predominant theoretical model to explain dissociative amnesia. However, current data point to altered connections between the cortico-hippocampal system, which manages episodic memory, and the amygdala system, responsible for emotional processing.

Disrupted brain connections

Neuroimaging research corroborates this hypothesis - of the breakdown of cerebral connections between the cortico-hippocampal and amygdala systems - showing that, under the effect of stress, the amygdala becomes hyperactive, while the hippocampus and prefrontal cortex see their regulatory functions diminish. This desynchronization, which is adaptive during trauma, is thought to lead to disturbances in the consolidation of memories, which remain fragmented and inaccessible to consciousness.

Animal studies also support this idea, highlighting the fact that this breakdown in connections between the hippocampus, cortex and amygdala is a protective response to trauma. However, this adaptive mechanism can leave lasting sequelae, notably dissociative amnesia, characterized by an inability to integrate memories in their spatio-temporal context.

Towards a better understanding of mechanisms

Scientific models agree that memories not integrated into a temporal or spatial context remain difficult to access in the conscious mind. This phenomenon could explain why some patients suffer from flashbacks or reliviscences, where memories reappear in the form of emotions or images with no clear narrative structure. As Géraldine Tapia points out:

these unintegrated memories are particularly likely to provoke uncontrolled reliving, linked to external triggers

Layton and Krikorian (2002)

Hypothesis: the amygdala mobilizes exponentionally with emotional intensity, impacting memory consolidation in the hippocampus.

Process: at high levels of stress, the amygdala begins to inhibit the hippocampus, limiting contextual consolidation in episodic memory, which impacts memory consolidation.

Consequences: memories are therefore mainly emotional and sensory, and their integration into a contextual episodic memory remains limited.

Elzinga and Bremner (2002)

Hypothesis: intense stress during a traumatic event damages the hippocampus and prefrontal cortex, while the amygdala is activated.

Process: the prefrontal cortex fails to inhibit the emotions generated by the amygdala, and the hippocampus is unable to organize memories coherently.

Consequences: memories are fragmented, appearing in the form of uncontrolled flashbacks.

Brewin et al (1996)

Hypothesis: traumatic memories can be divided into two types: verbal (VAM) and situational (SAM).

Process: VAM memories are accessible in conscious memory, while SAM memories emerge from conditions reminiscent of the trauma.

Consequences: VAM memories can be integrated and controlled, while SAM memories provoke uncontrollable flashbacks in response to specific triggers.

Methodological limitations

In a webinar organized by Cn2r in 2022, neuropsychology researcher Olivier Dodier critically analyzed the methodological and conceptual limitations of dissociative amnesia. In particular, he pointed to the variability of prevalences observed in retrospective studies, and the lack of clarity about the precise mechanisms of traumatic forgetting. He also spoke of the need to explore alternative explanations that go beyond dissociative amnesia.

The issue of false memories in dissociative amnesia

Following on from the methodological criticisms raised by Olivier Dodier, another key point of discussion concerns the formation of false memories. The phenomenon of false memories, often triggered by external influences or suggestive therapeutic processes, raises questions about the validity of certain cases of dissociative amnesia. Individuals firmly convinced of the existence of dissociative amnesia seem more inclined to report having experienced episodes of memory loss, even in the absence of tangible evidence15 . This phenomenon is particularly observed in therapeutic contexts, notably when techniques such as hypnosis or EMDR are misused to "recover" memories, by increasing patients' suggestibility, which can lead to the formation of erroneous or inaccurate memories. This does not apply to properly supervised practices, which provide clear benefits for patients.

The debate surrounding false memories is central to understanding dissociative amnesia, as it calls into question the reliability of recovered memories, particularly in a therapeutic setting. In reality, some of these memories could be mental constructs, shaped by expectations, cultural beliefs, or influenced by the therapeutic techniques themselves.

Variability of prevalence: retrospective studies show extremely variable rates (from 6% to 77%), making it difficult to reliably estimate the extent of the phenomenon.

Lack of information: studies fail to explain the mechanisms behind forgetting, confining themselves to general questions about memory loss without exploring its causes.

Think/No-Think paradigm: this model, often used to illustrate voluntary forgetting, does not correspond to the characteristics of dissociative amnesia, and its results are difficult to reproduce.

Weak correlations: correlations between the traumatic past and dissociation are considered weak to moderate, and the tools used do not accurately measure the dissociative amnesia described in the DSM.

Low-quality case studies: of the 128 studies identified, only two met DSM-5 criteria, with the majority offering no differential diagnosis or exploration of alternative hypotheses.

Conceptual limitation: the return of memory is both proof of amnesia and its refutation, raising an important question about the scientific validity of the concept.

Professional interviews

Read the interview "Traumatic memories in clinical practice" with Géraldine Tapia, lecturer in clinical psychopathology at Bordeaux University, in the pdf file.

You'll also find the section on legal implications, written by Laurence Bégon-Bordreuil, magistrate and legal advisor to the DIAV.

View the complete PDF file

The sources for this dossier are available in the pdf document.

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