Apparent amnesia on experimental memory tests in dissociative identity disorder: an exploratory study

Inter-identity amnesia for neutral episodic self-referential and autobiographical memory in Dissociative Identity Disorder: An assessment of recall and recognition

Amnesia is a core diagnostic criterion for Dissociative Identity Disorder (DID), however previous research has indicated memory transfer. As DID has been conceptualised as being a disorder of distinct identities, in this experiment, behavioral tasks were used to assess the nature of amnesia for episodic 1) self-referential and 2) autobiographical memories across identities. Nineteen DID participants, 16 DID simulators, 21 partial information, and 20 full information comparison participants from the general population were recruited. In the first study, participants were presented with two vignettes (DID and simulator participants received one in each of two identities) and asked to imagine themselves in the situations outlined. The second study used a similar methodology but with tasks assessing autobiographical experience. Subjectively, all DID participants reported amnesia for events that occurred in the other identity. On free recall and recognition tasks they presented a memory profile of amnesia similar to simulators instructed to feign amnesia and partial information comparisons. Yet, on tests of recognition, DID participants recognized significantly more of the event that occurred in another identity than simulator and partial information comparisons. As such, results indicate that the DID performance profile was not accounted for by true or feigned amnesia, lending support to the idea that reported amnesia may be more of a perceived than actual memory impairment.

Interidentity amnesia in dissociative identity disorder

INTRODUCTION

Patients diagnosed with dissociative identity disorder (DID) usually present with alternative personality states (alters) who take separate control of consciousness. Commonly, one alter will claim they have no awareness of events which took place when another alter was in control. However, some kinds of material are transferred across the alter boundary. Huntjens et al. devised an objective method of demonstrating such transfer.

METHODS

In the main study, following Huntjens et al., for three patients, two alters were taught different sets of nouns. The following week, one of the alters was given a recognition memory test including both sets plus distractor words. The patients in the Huntjens experiment responded in the same way to words in both sets.

RESULTS

In the present experiemnt, two of the patients tested had pairs of alters where there was no interference from the material which was presented to the other alter. In one of these cases, there was breakthrough with one pairing of alters, a pattern matched in a subsidiary experiment.

CONCLUSIONS

The population of individuals with DID are not homogeneous with respect to the depth of the blocking of episodic material from one alter to another.

Dissociative identity disorder: An empirical overview

OBJECTIVE

Despite its long and auspicious place in the history of psychiatry, dissociative identity disorder (DID) has been associated with controversy. This paper aims to examine the empirical data related to DID and outline the contextual challenges to its scientific investigation.

METHODS

The overview is limited to DID-specific research in which one or more of the following conditions are met: (i) a sample of participants with DID was systematically investigated, (ii) psychometrically-sound measures were utilised, (iii) comparisons were made with other samples, (iv) DID was differentiated from other disorders, including other dissociative disorders, (v) extraneous variables were controlled or (vi) DID diagnosis was confirmed. Following an examination of challenges to research, data are organised around the validity and phenomenology of DID, its aetiology and epidemiology, the neurobiological and cognitive correlates of the disorder, and finally its treatment.

RESULTS

DID was found to be a complex yet valid disorder across a range of markers. It can be accurately discriminated from other disorders, especially when structured diagnostic interviews assess identity alterations and amnesia. DID is aetiologically associated with a complex combination of developmental and cultural factors, including severe childhood relational trauma. The prevalence of DID appears highest in emergency psychiatric settings and affects approximately 1% of the general population. Psychobiological studies are beginning to identify clear correlates of DID associated with diverse brain areas and cognitive functions. They are also providing an understanding of the potential metacognitive origins of amnesia. Phase-oriented empirically-guided treatments are emerging for DID.

CONCLUSIONS

The empirical literature on DID is accumulating, although some areas remain under-investigated. Existing data show DID as a complex, valid and not uncommon disorder, associated with developmental and cultural variables, that is amenable to psychotherapeutic intervention.

Measuring fragmentation in dissociative identity disorder: the integration measure and relationship to switching and time in therapy

BACKGROUND

Some people with dissociative identity disorder (DID) have very little communication or awareness among the parts of their identity, while others experience a great deal of cooperation among alternate identities. Previous research on this topic has been sparse. Currently, there is no empirical measure of integration versus fragmentation in a person with DID. In this study, we report the development of such a measure.

OBJECTIVE

The goal of this study was to pilot the integration measure (IM) and to address its psychometric properties and relationships to other measures. The IM is the first standardized measure of integration in DID.

METHOD

Eleven women with DID participated in an experiment that included a variety of tasks. They filled out questionnaires about trauma and dissociation as well as the IM. They also provided verbal results about switching among alternate identities during the study sessions.

RESULTS

Participants switched among identities an average of 5.8 times during the first session, and switching was highly correlated with trauma. Integration was related to switching, though this relationship may be non-linear. Integration was not related to time in psychotherapy.

CONCLUSIONS

The IM provides a useful beginning to quantify and study integration and fragmentation in DID. Directions for future research are also discussed, including expanding the IM from this pilot. The IM may be useful in treatment settings to assess progress or change over time.

Inter-identity autobiographical amnesia in patients with dissociative identity disorder

Background

A major symptom of Dissociative Identity Disorder (DID; formerly Multiple Personality Disorder) is dissociative amnesia, the inability to recall important personal information. Only two case studies have directly addressed autobiographical memory in DID. Both provided evidence suggestive of dissociative amnesia. The aim of the current study was to objectively assess transfer of autobiographical information between identities in a larger sample of DID patients.

Methods

Using a concealed information task, we assessed recognition of autobiographical details in an amnesic identity. Eleven DID patients, 27 normal controls, and 23 controls simulating DID participated. Controls and simulators were matched to patients on age, education level, and type of autobiographical memory tested.

Findings

Although patients subjectively reported amnesia for the autobiographical details included in the task, the results indicated transfer of information between identities.

Conclusion

The results call for a revision of the DID definition. The amnesia criterion should be modified to emphasize its subjective nature.

Dissociative disorders

The dissociative disorders, including "psychogenic" or "functional" amnesia, fugue, dissociative identity disorder (DID, also known as multiple personality disorder), and depersonalization disorder, were once classified, along with conversion disorder, as forms of hysteria. The 1970s witnessed an "epidemic" of dissociative disorder, particularly DID, which may have reflected enthusiasm for the diagnosis more than its actual prevalence. Traditionally, the dissociative disorders have been attributed to trauma and other psychological stress, but the existing evidence favoring this hypothesis is plagued by poor methodology. Prospective studies of traumatized individuals reveal no convincing cases of amnesia not attributable to brain insult, injury, or disease. Treatment generally involves recovering and working through ostensibly repressed or dissociated memories of trauma; at present, there are few quantitative or controlled outcome studies. Experimental studies are few in number and have focused largely on state-dependent and implicit memory. Depersonalization disorder may be in line for the next "epidemic" of dissociation.

Memory transfer for emotionally valenced words between identities in dissociative identity disorder

The present study aimed to determine interidentity retrieval of emotionally valenced words in dissociative identity disorder (DID). Twenty-two DID patients participated together with 25 normal controls and 25 controls instructed to simulate DID. Two wordlists A and B were constructed including neutral, positive and negative material. List A was shown to one identity, while list B was shown to another identity claiming total amnesia for the words learned by the first identity. The identity claiming amnesia was tested for intrusions from list A words into the recall of words from list B and recognition of the words learned by both identities. Test results indicated no evidence of total interidentity amnesia for emotionally valenced material in DID. It is argued that dissociative amnesia in DID may more adequately be described as a disturbance in meta-memory functioning instead of an actual retrieval inability.

Procedural memory in dissociative identity disorder: When can inter-identity amnesia be truly established?

In a serial reaction time task, procedural memory was examined in Dissociative Identity Disorder (DID). Thirty-one DID patients were tested for inter-identity transfer of procedural learning and their memory performance was compared with 25 normal controls and 25 controls instructed to simulate DID. Results of patients seemed to indicate a pattern of inter-identity amnesia. Simulators, however, were able to mimic a pattern of inter-identity amnesia, rendering the results of patients impossible to interpret as either a pattern of amnesia or a pattern of simulation. It is argued that studies not including DID-simulators or simulation-free memory tasks, should not be taken as evidence for (or against) amnesia in DID.

Transfer of newly acquired stimulus valence between identities in dissociative identity disorder (DID)

Patients with Dissociative Identity Disorder (DID) frequently report episodes of interidentity amnesia, that is amnesia for events experienced by other identities. The goal of the present experiment was to test the implicit transfer of trauma-related information between identities in DID. We hypothesized that whereas declarative information may transfer from one identity to another, the emotional connotation of the memory may be dissociated, especially in the case of negative, trauma-related emotional valence. An evaluative conditioning procedure was combined with an affective priming procedure, both performed by different identities. In the evaluative conditioning procedure, previously neutral stimuli come to refer to a negative or positive connotation. The affective priming procedure was used to test the transfer of this acquired valence to an identity reporting interidentity amnesia. Results indicated activation of stimulus valence in the affective priming task, that is transfer of emotional material between identities.

Directed forgetting between, but not within, dissociative personality states

To investigate amnesia between identities in dissociative identity disorder (DID), the authors assessed explicit and implicit memory performance on a directed-forgetting task in 12 DID patients who switched from one state to an "amnesic" state between presentation and memory testing. DID patients were instructed either to remember or to forget neutral and emotional words. Besides an overall decrease in explicit memory, patients demonstrated selective forgetting of to-be-forgotten, but not of to-be-remembered words in the amnesic state. Patients did not exhibit any directed forgetting within the same state. Implicit memory was fully preserved across states. Independent of state, patients recalled more emotional than neutral information. These results may extend the conceptualization of memory processes in DID, suggesting an important role for retrieval inhibition.

Perceptual and conceptual priming in patients with dissociative identity disorder

The present study examined implicit memory transfer in patients with dissociative identity disorder (DID). To determine priming impairments in DID, we included both several perceptual priming tasks and a conceptual priming task using neutral material. We tested a large sample of DID patients (n = 31), in addition to 25 controls and 25 DID simulators, comparable on sex, age, and education. Controls replicated conceptual priming results of Vriezen, Moscovitch, and Bellos (1995) by showing that conceptual priming seems to require the formation of domain-specific semantic representations, denoting either sensory or functional object attributes. We extended a study performed by Schacter, Cooper, and Delaney (1990) by demonstrating priming for impossible object using the sensitive priming index of response times. The simulators in the study were not able to simulate interidentity amnesia on the implicit memory tasks employed. Partly in contrast to participants in previous studies, DID patients showed evidence of perceptual priming as well as conceptual priming comparable to that of controls. DID patients thus displayed normal implicit memory performance.

Alters in dissociative identity disorder. Metaphors or genuine entities?

How should the different identities (i.e., alters) that are thought to be typical for dissociative identity disorder (DID) be interpreted? Are they just metaphors for different emotional states or are they truly autonomous entities that are capable of willful action? This issue is important because it has implications for the way in which courts may handle cases that involve DID patients. Referring to studies demonstrating that alters of DID patients differ in their memory performance or physiological profile, some authors have concluded that alters are more than just metaphors. We argue that such line of reasoning is highly problematic. There is little consensus among authors about the degree to which various types of memory information (implicit, explicit, procedural) may leak from one to the other alter. Without such theoretical accord, any given outcome of memory studies on DID may be taken as support for the assumption that alters are in some sense "real." As physiological studies on alter activity often lack proper control conditions, most of them are inconclusive as to the status of alters. To date, neither memory studies nor psychobiological studies have delivered compelling evidence that alters of DID patients exist in a factual sense. As a matter of fact, results of these studies are open to multiple interpretations and in no way refute an interpretation of alters in terms of metaphors for different emotional states.

Toward an etiology of dissociative identity disorder: a neurodevelopmental approach

This article elaborates on Putnam's "discrete behavioral states" model of dissociative identity disorder (Putnam, 1997) by proposing the involvement of the orbitalfrontal cortex in the development of DID and suggesting a potential neurodevelopmental mechanism responsible for the development of multiple representations of self. The proposed "orbitalfrontal" model integrates and elaborates on theory and research from four domains: the neurobiology of the orbitalfrontal cortex and its protective inhibitory role in the temporal organization of behavior, the development of emotion regulation, the development of the self, and experience-dependent reorganizing neocortical processes. The hypothesis being proposed is that the experience-dependent maturation of the orbitalfrontal cortex in early abusive environments, characterized by discontinuity in dyadic socioaffective interactions between the infant and the caregiver, may be responsible for a pattern of lateral inhibition between conflicting subsets of self-representations which are normally integrated into a unified self. The basic idea is that the discontinuity in the early caretaking environment is manifested in the discontinuity in the organization of the developing child's self.

Dissociative identity disorder and memory dysfunction: the current state of experimental research and its future directions

Memory dysfunction is a central feature of dissociative identity disorder (DID). Following the memorial anomalies outlined by Putnam [Putnam, F. W. (1994). Dissociation and disturbances of self. In: D. Cicchetti & S. L. Toth (Eds.), Disorders and dysfunctions of the self, vol. 5 (pp. 251-265). Rochester, NY: University of Rochester Press; Putnam, F. W. (1995). Development of dissociative disorders. In: D. Chicchetti & D. J. Cohen (Eds.), Developmental psychopathology, vol. 2 (pp. 581-608). New York: Wiley], the experimental research using DID case studies and samples is reviewed. As a whole, research suggests that amnesic barriers between alter personalities are typically impervious to explicit stimuli, as well as conceptually driven implicit stimuli. Autobiographical memory deficits are also experimentally evident in DID. Although no experimental studies have addressed the issue of source amnesia or pseudomemories, there is some evidence that pseudomemories are an infrequent but real phenomenon in DID patients. Finally, potential deficits in working memory are outlined, including those relating to cognitive inhibition. Research directions are discussed throughout to further elucidate the nature of memory dysfunction in DID.

Memory dissociation: the approach to the study of retrieval processes

The phenomenon of dissociated memory retrieval is observed when some influences (for example, pharmacological) on the brain result in specific changes of long-term memory. The purpose of present paper is to reveal possibilities of the phenomenon for study of long-term memory retrieval. Pharmacologically-induced dissociated states could be identified when the retrieval of responses learned before treatment is temporarily blocked by the drug influence, but the ability of the animals to learn new tasks is intact. Furthermore, memory traces that were formed in drugged state are not accessible for the retrieval in normal state and only the same drug treatment allows retrieving them. In the present work, dissociated learning of food-motivated tasks was carried out in Wistar rats with cholinesterase inhibitor physostigmine (0.5 mg/kg, intraperitonealy) or general anaesthetic sodium pentobarbital (15 mg/kg, intraperitonealy.). The retrieval of dissociated responses was studied under the influence of various doses of the same drugs. The results revealed the asymmetry of memory dissociation with physostigmine in contrast to pentobarbital-induced memory dissociation. Gradual access for the retrieval of dissociated memory traces after pharmacological modulation of cholinergic and GABA-ergic brain systems was shown. It was suggested an important role of hippocampus in memory dissociation, as a structure-performing match-mismatch operations between different retrieved memory traces.