Link to a list of papers on dissociative disorder.

Dissociative Disorders

John F. Kihlstrom

University of California, Berkeley

Note:  An edited version of this article was published in the Annual Review of Clinical Psychology, Vol. 1(2005).

amnesia, fugue, multiple personality, trauma, memory, identity

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 reveals 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 have focused largely on state-dependent and implicit memory, are few in number. Depersonalization disorder may be in line for the next "epidemic".

The dissociative disorders includes a wide variety of syndromes whose common core is an alteration in consciousness that affects memory and identity. In the Diagnostic and Statistical Manual (DSM; American Psychiatric Association 1994), the nosological category includes four major entries:

Dissociative Amnesia -- formerly, psychogenic amnesia: patients suffer a loss of autobiographical memory for certain past experiences.

Dissociative Fugue -- formerly, psychogenic fugue: the amnesia covers the whole (or, at least, a large part) of the patient’s life; it is also accompanied by a loss of personal identity and, in many cases, physical relocation (hence its name).

Dissociative Identity Disorder (DID) -- formerly multiple personality disorder (MPD): a single patient appears to possess and manifest two or more distinct identities (a "host personality" or "host" and one or more "alter egos", "alters", or "ego states") that alternate in control over conscious experience, thought, and action, and typically separated by some degree of amnesia.

Depersonalization Disorder: patients believe that they have changed in some way, or are in some way no longer real (in derealization, the same beliefs are held about the patient’s surrounding environment.

Dissociative Disorders Not Otherwise Specified: patients display some dissociative symptoms, to some degree, but not to the extent that they qualify for one of the major diagnoses. This category includes certain culturally specific "spirit-possession" states, such as amok (in Indonesia), latah (Malaysia), and ataque de nervios (Latin America). It also includes Ganser syndrome -- presumably on the assumption that the patient’s vague and approximate answers to questions reflect some kind of memory disorder.

While impairments of memory and consciousness feature prominently in certain neurological disorders, from the amnesic syndrome to concussion and coma, the dissociative disorders are "functional" in nature. This does not mean that they have no organic basis: all mental states and conditions are ultimately rooted in neural activity, and recent advances in brain-imaging technology offer the promise of revealing the neural correlates of the dissociative disorders. Rather, it means that the dissociative disorders are not instigated by some palpable insult, injury, or disease affecting the brain. For this reason, the dissociative disorders were historically grouped with the conversion disorders under the broad rubric of "hysteria".

Historically, the dissociative disorders were also considered among the rarest forms of psychopathology. An exhaustive review found only 76 cases reported between 1791 and 1944 (Taylor & Martin); almost 20 years later, an update added only a single case, the famous Three Faces of Eve (Sutcliffe & Jones 1962). Eve was followed by Evelyn (Osgood et al 1976) -- though Thigpen and Cleckley themselves, who worked with Eve, reported that despite hundreds of referrals they never saw another valid case (Thigpen & Cleckley 1984).

However, the late 1980s and 1990s witnessed what might be thought of an "epidemic" (Boor 1982, p. 302) of multiple personality disorder, manifested in an avalanche of case reports and case series, books, journal articles, and conferences devoted to the topic. For example, in contrast to the 8 case reports of MPD published between 1944 and 1970, 36 were published between 1970 and 1979 (Greaves 1980). Putnam and his colleagues developed a case registry of 100 cases "currently or recently in treatment" as of 1982 (Putnam et al 1986, p. 286), while Kluft analyzed outcomes for 171 patients who had been diagnosed with MPD (Kluft 1984). The International Society for the Study of Multiple Personality and Dissociation (renamed the International Society for the Study of Dissociation) held its first annual conference in 1984. Its official journal, Dissociation, first appeared in 1988, superceded in 2000 by the Journal of Trauma and Dissociation. The first scholarly monographs devoted to multiple personality disorder also appeared at this time (Bliss 1986, Ross 1986).

The present review begins at this point, with an emphasis on work published since 1990 (the literature review for this article ended July 1, 2004). More comprehensive surveys, including much historical material, can be found elsewhere (Kihlstrom 1992, Kihlstrom 1994, Kihlstrom 2001, Kihlstrom et al 1993, Lynn & Rhue 1994, Michelson & Ray 1996).

The dissociative disorders were first labeled as such in the third edition of DSM (American_Psychiatric_Association 1980); before that, they were classified simply as forms of psychoneurosis or of hysteria. Unfortunately, when that edition of DSM was revised (American_Psychiatric_Association 1987), interpersonality amnesia was eliminated as a diagnostic feature of MPD – an error which may have contributed to the increasing frequency with which this once-rare condition was diagnosed. To some degree, this error was corrected in the fourth edition (American_Psychiatric_Association 1994), which also renamed MPD as DID, to emphasize the importance of changes in consciousness and identity, rather than personality. Without the criterion of amnesia, multiple personality disorder (dissociative identity disorder) is difficult to differentiate from atypical dissociative disorder (now called dissociative disorder not otherwise specified). But even with the criterion of amnesia reinstated, difficulties defining such terms as personality, identity and ego state – not to mention amnesia itself -- can inject an unacceptable level of subjectivity into the diagnosis.

Even with relatively strict criteria in place, it can be difficult to discriminate between the dissociative disorders and bipolar disorder, borderline personality disorder, and even schizophrenia. When enthusiastic clinicians are determined to find it, DID can be diagnosed merely from the normal situational variability of behavior, or instances where otherwise "normal" people just "don’t feel like themselves" (Piper 1995). This is especially the case if the clinician believes that DID is a "superordinate" diagnosis, such that presenting symptoms such as phobias, obsessions, and compulsions, which might normally call for a primary diagnosis of anxiety disorder, can be attributed to one of a patient’s alter egos instead (Putnam et al 1984); or if it is believed that alter egos can appear only once in the patient’s life, in order to perform some specific task, never to be manifest again (Bliss 1980, Kluft 1991).

Perhaps because they were considered to be rare, the dissociative disorders were not included in the Structured Clinical Interview for Diagnosis (SCID) developed in an effort to make psychiatric diagnoses more reliable (First et al 1997, Spitzer 1990). However, this omission was quickly corrected by development of a freestanding SCID protocol for dissociative disorders (SCID-D; Steinberg 1994, Steinberg et al 1990, Steinberg 1996). An alternative Dissociative Disorders Interview Schedule has also been developed (Ross et al 1989), but the SCID-D has become the "gold standard" for diagnosis in this area. The Clinician-Administered Dissociative States Scale (Bremner et al 1997), intended to measure episodic dissociative states, focuses on symptoms of depersonalization and derealization, and not the disruptions of memory and identity that lie at the core of the dissociative disorders.

A number of questionnaires have been developed for the assessment of dissociative tendencies in both clinical and research settings (Kihlstrom et al 1994). The most popular of these is the Dissociative Experiences Scale (DES; Bernstein & Putnam 1986, Carlson & Putnam 1993), which has proved useful as an instrument for screening those who might be at risk for dissociative disorder (Carlson et al 1993, Putnam et al 1996). Alternative instruments include the Perceptual Alterations Scale (PAS; Sanders 1986), the Questionnaire on Experiences of Dissociation (Riley 1988), the Dissociation Questionnaire (DIS-Q; Vanderlinden et al 1991), the Dissociative Processes Scale (DPS; Watson 2003), and the Mini-SCID-D (Steinberg et al 1992). Although not all of these scales have been brought together in any single experiment, the available evidence indicates that all of them are strongly intercorrelated (Gleaves et al 1995, Kihlstrom et al 1994). However, except for the Mini-SCID-D, which is closely modeled on the SCID-D, all of them are also heavily loaded with absorption, a feature of normal personality reflecting the individual’s tendency to alter consciousness by markedly narrowing or expanding his or her focus of attention and blurring the boundary between self and world (Roche & McConkey 1990, Tellegen & Atkinson 1974). Absorption, in turn, is related to the related to the "openness" dimension of the "Big Five" structure of personality (Glisky et al 1991).

Good data on the incidence and prevalence of the dissociative disorders is hard to come by. These syndromes were excluded from the Epidemiological Catchment Area survey (Regier et al 1984, Robins et al 1984), presumably because of their assumed rarity, and the lack of appropriate standardized diagnostic instruments and criteria. At the height of clinical interest in the dissociative disorders, the Clinton administration’s Task Force on Health Care Financing Reform received a report claiming an prevalence of dissociative disorder of "about ten percent in the general population" (Loewenstein 1994, p. 3), including a rate of 7% for psychogenic amnesia and 1.3% for multiple personality disorder. On the other hand, a study of a large acute psychiatric hospital, employing the SCID-D to diagnose DID, yielded an estimated rate of only 1% among recent admissions (Rifkin et al 1998). If this figure is representative, of course, the prevalence of DID in the population as a whole is likely to be considerably lower.

An interesting feature of the DID "epidemic" is an increase not just in the number of cases, but also in the number of alter egos reported per case. In the classic literature, the vast majority of cases were of dual personality (Sutcliffe & Jones 1962, Taylor & Martin 1944). By contrast, most of the new cases complied by Greaves presented at least three personalities (Greaves 1980); in two other series, the average number of alter egos was more than 13 (Kluft 1984, Putnam et al 1986). As Kenny (Kenny 1986) noted, it was almost as if there were some kind of contest to determine who could have (or be) the patient with the most alter egos. The famous Eve, of course, appeared to have three personalities (Osgood & Luria 1954, Thigpen & Cleckley 1954). But when popular and professional interest in MPD was stimulated by the case of Sibyl, who was reported to possess 16 different personalities (Schreiber 1973), Eve replied with her own account of her illness, eventually claiming 22 (Sizemore & Huber 1988). Despite the almost-infinite number of possible synaptic connections in the brain, one might say that the mind simply is not big enough to hold so many personalities. The proliferation of alter egos within cases, as well as the proliferation of cases, has been one of the factors leading to skepticism about the disorder itself.

Commonly used DES cutscores identify some 5-15% of individuals in the general population as "at risk" for dissociative disorder (Kihlstrom et al 1994) – a figure that is almost certainly inflated by the presence on the scale of many items tapping normal levels of absorption. A taxometric analysis of the DES (Waller et al 1996), suggested that "approximately 3.3% of the general population belongs to a pathological dissociative taxon" (Waller & Ross 1997, p. 499) reporting frequent and profound experiences of amnesia and/or depersonalization. However, Watson (Watson 2003) found that assessments of the dissociative taxon showed extremely low test-retest reliability coefficients – casting the existence of a dissociative taxon itself into doubt. If consistent membership in the "pathological dissociative taxon" is the standard, dissociative disorder is present in about 1% of the college student population. Even if this figure is accurate, most cases are probably accounted for by depersonalization disorder – which, like DID, has also experienced an upsurge of recent interest (Simeon et al 1998a). It should be remembered, however, that scales like the DES are really intended for economical screening of large groups of subjects – a process that is likely to yield a substantial number of false positives. At best they can identify individuals who might be at risk for dissociative disorder – any provisional diagnosis should be confirmed by structured diagnostic interviews such as the SCID-D.

Historically, the dissociative disorders have been attributed to pathological levels of psychological stress, which are held to disrupt the normal integration of personality and mental life, so that some aspects of experience, thought, and action are split off from consciousness – hence the term "dissociation". Traditionally, for example, both dissociative amnesia and dissociative fugue are generally held to occur in response to some kind of trauma – traumatic stress being the "psychogenic" cause implied by their earlier labels. The "trauma-memory argument" (Kihlstrom 1995, Kihlstrom 1996, Kihlstrom 1997, Kihlstrom 1998) asserts that trauma victims typically (often, sometimes) deploy psychological defenses such as repression or dissociation to block their awareness of the trauma. The resulting amnesia is psychogenic in nature, in that it is ostensibly caused either by the traumatic stress itself or by the defenses deployed against it. For example, van der Kolk has argued that traumatic stress interferes with the consolidation of a consciously accessible narrative memory, but enhances nonverbal, sensory, motor, and affective representations of the trauma (van der Kolk 1994, van der Kolk & van der Hart 1991). Similarly, Metcalfe and Jacobs have argued that the Yerkes-Dodson law predicts amnesia under high levels of emotional stress (Metcalfe & Jacobs 1996, Metcalfe & Jacobs 1998, see also Nadel & Jacobs 1998).

As it happens, a plausible traumatic origin can be identified in most cases of amnesia and fugue – for example, sexual assault (Eisen 1989, Kaszniak et al 1988), physical assault (Glisky et al 2004), or the death of a family member (Schacter et al 1982). On the other hand, a trauma history is sometimes absent (Dalla Barba et al 1997) – as it was in the very first reported case of fugue, that of Ansel Bourne (James 1890/1980, Kenny 1986). The fact is, trauma is not difficult to find if one searches for it with a suitably broad definition of the concept (Harvey & Bryant 2002, McNally 2003). But even when the trauma seems unequivocal there is the additional difficulty of showing that the trauma caused the amnesia, and explicating the psychological (not to mention neurological) mechanisms by which this might occur.

In the recent revival of interest in the dissociative disorders, DID is commonly attributed to prolonged, overwhelming trauma, particularly incest and other forms of childhood sexual abuse (Putnam et al 1986, Spiegel 1984). However, the evidence in this respect consists entirely of retrospective self-reports made by the patients themselves, often without any independent corroboration (Gleaves 1996). We do not know how much such reports reflect the patients’ vivid imagination, their implicit theories of their problems, or their therapists’ suggestions – including suggestions made while the patients are hypnotized (Frankel 1990, Frankel 1991a, Frankel 1991b, Frankel 1993). Even when such corroboration is available, the extremely broad and flexible definition of trauma makes interpretation problematic. Moreover, this body of research rarely provides a comparison group of patients carrying other diagnoses (or, for that matter, nonpatients) showing that such trauma is a specific causal factor in DID, as opposed to other syndromes (Piper 1995, Piper 1997). The difficulties of attributing symptoms of any sort, dissociative or not, to childhood trauma are well known, and include obvious errors such as backwards reasoning (Rind 2003, Sbraga & O'Donohue 2003) as well as more subtle problems caused by conditioning on the consequent (Dawes 1993). Even in the present state of the evidence, the simple fact is that DID and other dissociative disorders simply do not figure as prominent outcomes in the literature on the effects of childhood physical and sexual abuse (Kendall-Tackett & Marshall 1998, Kendall-Tackett et al 1993, Rind & Harrington 1995, Rind et al 1998, Rind et al 2000, Rind et al 2001). The bottom line is that while it is plausible that the dissociative disorders have their origins in trauma, the presently available evidence for such an etiology is far from convincing.

In this context, one of the most interesting features of the recent literature has been a vigorous debate concerning the validity of trauma-memory argument itself. Proponents frequently cite the literature on disaster victims, combat, prisoners and torture victims, and victims and perpetrators of violent crime (e.g., Arrigo & Pezdek 1997, Brown et al 1998, Gleaves et al 2004, Scheflin & Brown 1996) as consistent with a clinical folklore that goes back to the writings of Janet, and Freud in the 19^th century. To the contrary, Pope and his colleagues reviewed 63 studies of documented trauma victims, including more than 10,000 subjects, and failed to find even a single convincing case of amnesia for the traumatic event that could not be explained by organic factors, infantile and childhood amnesia, ordinary forgetting, or other normal memory processes (Pope et al 1998, Pope et al 2000). Most trauma victims remember their experiences all too vividly – an empirical fact that is consistent with what is known from the laboratory about arousal and memory (Cahill & McGaugh 1998). Whatever forgetting occurs appears not to be the product of psychological defenses such as repression or dissociation.

On the other hand, Brown and his colleagues have argued that at least nine of the studies cited by Pope and his colleagues do, in fact, offer evidence for traumatic amnesia ( see also Brown et al 1998, Brown et al 1999). However, re-examination of the evidence supports Pope’s initial conclusions (Piper et al 2000). For example, two individuals who were amnesic for a lightning strike were "side-flash" victims who received the equivalent of electroconvulsive shock; some of the children who were amnesic for a flood disaster were as young as two years old at the time of the incident; and while approximately one-third of older children who were earthquake survivors were reported as showing psychogenic amnesia for the event, more than two-thirds of a control group of children who were not exposed to the trauma met the same criterion. One study did report a high rate of dissociative symptoms, as measured by the DES, among those who experienced the Loma Prieta earthquake of 1989 (Cardena & Spiegel 1993), but these were most likely common experiences of depersonalization and derealization; there was no evidence that any subject forgot the earthquake.

In the face of such evidence, the trauma-memory argument is sometime revised to take special note of trauma associated with incest and other childhood sexual abuse. For example, Terr has suggested that memory is enhanced for "Type I" traumas involving single, surprising, well-defined events, while denial, psychic numbing, and dissociation create amnesia for "Type II" traumas, such as incest, which are repeated over an extended period of time (Terr 1994, Terr 1991). Similarly, Freyd has argued that memory is enhanced for "terror" traumas, such as combat, but impaired by dissociation for "betrayal" traumas, such as incest (Freyd 1996, Freyd 1994).

Each of these theories has its own set of problems (Shobe & Kihlstrom 1997), but the foremost problem is that there is no good evidence that childhood sexual abuse is associated with amnesia. In response to the critiques of the trauma-memory literature by Pope and his colleagues, Brown and his colleagues reviewed the literature on "naturally occurring dissociative or traumatic amnesia for childhood sexual abuse", and concluded that "Not a single one of the 68 data–based studies failed to find it" (Brown et al 1999, p. 126). Among the studies most frequently cited by proponents of the trauma-memory argument is a prospective study by Williams, which found that 38% of a group of women who had suffered documented sexual abuse as children failed to report it to an interviewer some 17 years later (Williams 1994a, Williams 1994b). On the other hand, the difficulties attending this type of research are well known (Kihlstrom 1995, Kihlstrom 1996, Kihlstrom 1998, Loftus et al 1994, Pope & Hudson 1995a, Pope & Hudson 1995b, Pope et al 1998). For example, although Williams did have satisfactory independent corroboration of the traumatic events, she failed to distinguish between traumatic repression and ordinary time-dependent forgetting, infantile and childhood amnesia, or even a simple reluctance to report embarrassing memories to a stranger. This last problem is particularly acute when the events in question are embarrassing or otherwise upsetting, and often requires a clarification interview (Della Femina et al 1990). Genuine memory failures are not commonly found in careful inquires of individuals who were abused as children – so long as they were old enough to encode the memory properly in the first place (Goodman et al 2003, Widom & Morris 1997, Widom & Shepard 1996).

In view of this body of evidence, theories that attempt to describe the psychological or biological processes by which trauma induces amnesia (Freyd 1996, Metcalfe & Jacobs 1998, Nadel & Jacobs 1998, van der Kolk 1994) appear to be rendered moot by the apparent fact that trauma-induced psychogenic amnesia occurs rarely if at all. Even the widely discussed case study of Jane Doe (Corwin & Olafson 1997), sometimes presented as a compelling "existence proof" of traumatic amnesia and recovered memory, is in fact quite ambiguous (Loftus & Guyer 2002a, Loftus & Guyer 2002b). Genuine cases of dissociative amnesia, fugue, and dissociative identity disorder do appear to involve functional amnesia (Kihlstrom & Schacter 2000, Kopelman 1995), and it would not be surprising if some patients with dissociative disorder have histories of child sexual trauma. But there is no reason to think that either the syndromes themselves, or the amnesia that is symptomatic of them, are caused by trauma, repression, or dissociation.

Nor is there any reason to think that recovered memories of trauma are valid on their face, and not in need of corroboration. It should surprise no one if claims of recovered traumatic memories are occasionally corroborated (Cheit 1998, Cheit 1999, Schooler 2001). But the recovery of a traumatic memory, even one that is independently corroborated, does not by itself imply that the event was forgotten due to repression or dissociation (Piper 1999). Researchers must be careful to distinguish between recoveries mediated by the lifting of repression or breaching of dissociation from other causes of remembering, including the normal effects of shifting retrieval cues, reminiscence effects, and hypermnesia. The recovery of a forgotten trauma may be no different in kind that the recovery of one’s memory for where one put the car keys, or the name of one’s third-grade teacher. It is also important to distinguish between the recovery of a forgotten memory of trauma and a reinterpretation of an event that had always been remembered.

For all the increased attention devoted to the dissociative disorders over the past 20 years, not to mention the apparent increase in prevalence, it is remarkable that so little is known about their treatment. Aside from individual case reports, there appear to be no systematic empirical outcome studies of either dissociative amnesia or dissociative fugue (Loewenstein 1994, Maldonado et al 2002). Following traditions that originated in wartime, clinicians sometimes employ barbiturate drugs (the "amytal interview" or "narcosynthesis") or hypnosis to stimulate the recovery of repressed or dissociated memories. Nevertheless, there are no systematic studies of the effectiveness of drugs in recovering valid memories (Piper 1993). Moreover, research offers no reason to think that hypnosis facilitates the recovery of repressed or dissociated memories, and every reason to think it can distort memory (Kihlstrom & Eich 1994). Memories recovered through these and similar techniques cannot be taken at face value, and must be subject to independent corroboration. Apparently, many cases of amnesia and fugue remit spontaneously, a process that perhaps can be helped along by presenting the patient with appropriate retrieval cues if they are available.

There is a more extensive literature on the treatment of DID (Loewenstein 1994, Maldonado et al 2002). Although there are some examples of cognitive-behavioral therapy (Kirsch & Barton 1988), most current therapeutic approaches to are predicated on the notion that DID is caused by childhood trauma, such as sexual and physical abuse. Typically, the therapy is psychodynamic and insight-oriented, focusing on uncovering, abreacting, working through the trauma and other conflictual issues presumed to underlie the disorder, and getting the patient to abandon dissociative defenses. The therapist also seeks to integrate the patient’s alter egos into a single cohesive identity – meaning that therapeutic alliances must be established not only between each alter ego and the therapist, but also among the alter egos themselves.

Given these tasks, it is not surprising that the treatment of DID patients is arduous and uncertain. A pioneering study by Kluft, employing a rigorous set of clinical criteria, found that 67% of 123 DID patients had achieved "fusion" for at least 3 months following approximately two years of intensive treatment, with 23% maintaining fusion for at least 27 months (Kluft 1984); the percentages increased with further treatment (Kluft 1986), so that a decade later 84% of the original sample met a rigorous criterion for stable fusion (Kluft 1994). In another study, Ellason and Ross reported that 12 of 54 patients (from an original sample of 135) who could be contacted two years after treatment began had achieved a therapeutic goal of stable integration and reduced scores on the DES (Ellason & Ross 1997). Depending on how we count, this is a success rate of 9-22%.

Although the Ellason and Ross study did involve quantitative endpoints, the lack of a standard treatment protocol and of an untreated control group makes even these positive outcomes difficult to evaluate (Merskey & Piper 1998, Powell & Howell 1998, for a reply, see Ross & Ellason 1998). Equally critical is the absence of alternative treatments. For example, if there is no causal link between CSA and DID, then it would seem pointless to focus therapy on the recovery and working through of traumatic memories that may well be false or distorted. Moreover, the process of identifying, negotiating with, and integrating the patient’s alter egos may actually encourage and reinforce dissociative symptomatology (Bowers 1991, Piper 1995, Piper 1997) – a situation which may account for the increase in number of alter egos per DID case noted earlier. Accordingly, it would seem desirable to develop and test alternative therapeutic approaches that might minimize these risks, and be more cost-effective.

As remarkable as the absence of controlled, or at least quantitative, outcome studies of DID is the dearth of experimental studies of the dissociative disorders. For example, there have been only a few attempts to document personality differences among a patient’s alter egos with standardized personality testing. In both the "Eve" and "Evelyn" cases, the three alter egos all completed the semantic differential (Kroonenberg 1985, Osgood & Luria 1954, Osgood et al 1976). In the "Jonah" case, each of five alter egos received the WAIS, MMPI, and Gough Adjective Check List (Brandsma & Ludwig 1974, Ludwig et al 1972). A handful of other studies have used the MMPI or the Rorschach, mostly to confirm the clinical impression of personality. Psychophysiological measures (Putnam 1984), including brain-imaging methods (Tsai et al 1999), have been put to much the same use (Merckelbach et al 2002). Not surprisingly, most experimental research on the dissociative disorders has focused on memory functions in fugue and DID (Dorahy 2001, Kihlstrom & Schacter 1995, Kihlstrom & Schacter 2000, Kopelman 2002, Schacter & Kihlstrom 1989).

Testing of autobiographical memory indicates that the amnesia in fugue states is retrograde, not anterograde – that is, fugue patients are amnesic for "premorbid" events that occurred prior to the onset of the fugue state, but not for "posmorbid" events that occurred after the fugue began (Dalla Barba et al 1997, Glisky et al 2004, Kopelman et al 1994, Schacter et al 1982). After the fugue has remitted, of course, memory for premorbid events is restored. However, the amnesia for premorbid events is replaced by one covering the fugue itself (Schacter et al 1982). During the fugue state, access to semantic memory is generally preserved (Dalla Barba et al 1997, Glisky et al 2004, but see Kopelman et al 1994, Schacter et al 1982) – except, of course, for semantic knowledge about the patient’s own identity.

The fate of autobiographical memory in DID depends on which alter ego is being tested, and the pattern of interpersonality amnesia – symmetrical, with two alters unaware of each other, or asymmetrical, with one aware and the other not. In one case, testing revealed a profound childhood amnesia covering the first 14 years of the patient’s life, suggesting that what initially appeared to be the host personality might instead be an alter ego that emerged during adolescence (Schacter et al 1989). Unfortunately, circumstances precluded testing the memories of other alter egos. In another an adult alter ego showed the recency bias in autobiographical memory recall characteristic of normal performance, but a 9-year-old alter ego had no memories dated after age 12 (Bryant 1995). Coincidentally, this patient had also been tested before the DID diagnosis had been made. Before diagnosis, she had the usual distribution of childhood memories; after diagnosis, childhood memories were almost completely absent in the host personality – though they did appear in the child alter.

Note that in none of these studies was it possible to verify the memories reported by the patients in their various alter egos. However, studies employing standard verbal-learning paradigms have generally confirmed clinical impressions of interpersonality amnesia. That is, one alter ego is typically unable to recall or recognize words or pictures that had been studied by another (Eich et al 1997b, Nissen et al 1988). Directed forgetting effects are stronger between alter egos than within a single alter (Elzinga et al 2001) – though, interestingly, there were no differences between emotional and neutral stimulus materials.

The amnesias observed in fugue and DID affect conscious recollection, begging the question of the fate of implicit memories. Early experimental case studies did, in fact, suggest that implicit memories can transfer between personalities even when explicit memories do not (Dick-Barnes et al 1987, Ludwig et al 1972, Silberman et al 1985). On the other hand, the first formal comparison yielded some complications (Nissen et al 1988): explicit memory generally did not transfer among eight mutually alter egos of a single DID patient; but while some implicit tests (priming in word- and picture-fragment completion, perceptual identification, and sequence learning) showed transfer, others (priming in word-stem completion, sentence interpretation, picture puzzles, and free association) did not. Similarly, a study involving 9 patients showed priming on picture-fragment completion, but not on word-fragment completion (Eich et al 1997b); simulators did not show this same pattern of task performance (Eich et al 1997a). Neither a single case of fugue (Kopelman et al 1994) nor a study of four DID patients (Peters et al 1998) found priming on a word-stem completion test. On the other hand, a study of directed forgetting 12 patients found preserved priming on perceptual-identification and picture-fragment completion tasks (Elzinga et al 2001). Thus, whether implicit memory is spared in interpersonality amnesia depends on the nature of the implicit memory test.

Interpretation of these and the earlier results is generally bedeviled by investigators’ failure to settle on a common set of tasks, from which a stable corpus of replicable results might emerge. It might be that implicit memory is spared on "structural" implicit memory tasks that are mediated by a perception-based representation of the stimulus material, but not on "semantic" tasks mediated by meaning-based representations. On the other hand, both word-stem and word-fragment completion are structural in nature, but they yield different results. Although superficially similar, word-stem completion tasks often allow a number of correct answers, while word-fragment completion tasks permit only one; accordingly, word-fragment completion is typically construed by subjects as a problem to be solved, while word-stem completion is typically construed perceived as something akin to free association. Future research should take account of both the precise nature of the implicit memory tasks, but also subjects’ attitude mental set when performing them – as well, perhaps, as the relevance of the stimulus materials to the "personality" of the alter ego being tested.

The distinction between explicit and implicit memory proved crucial to understanding an unusual case of fugue in which the patient lost use of his native language (German), as well as his identity and fund of autobiographical memory (Glisky et al 2004). In one experiment, this patient showed enhanced skin conductance responses to personally relevant material, such as the names of family and friends. In another, he performed perfectly on a task involving learning pairs of semantically related German and English words, compared to unrelated word pairs and pairs including German nonwords. He also showed faster response latencies in a lexical decision task involving German words, compared to English and German nonwords, while fMRI imaging revealed a shift from frontal to parietal activity. On all three tests, behavioral and neurimaging, German speakers instructed to simulate ignorance of German showed a very different patterns of performance.

The dissociative disorders are functional in nature, in that they are not instigated by brain insult, injury, and disease, but that does not mean that there are no neural correlates of dissociative pathology. The fact that the amnesias in the dissociative disorders are reversible marks them as disruptions of memory retrieval, as opposed to encoding or storage failures; the observed dissociations between explicit and implicit memory are also consistent with retrieval failure. According to one prominent theory, the encoding and retrieval of episodic memories preferentially activates the left and right prefrontal cortex, respectively (Habib et al 2003, Nyberg et al 1996). Accordingly, in functional amnesia we might expect to observe anomalies in the activity of right-hemisphere structures associated with memory processing. Broadly consisent with these suggestions, SPECT (Markowitsch et al 1997a), PET (Markowitsch et al 1997b) and imaging in single cases of psychogenic amnesia and fugue revealed diminished activity in right frontal and temporal structures during autobiographical memory tasks (Markowitsch 1999). Of course, the precise pattern of neuroimaging findings will depend on the details of the particular case, such as whether the patient has lost conscious access to some or all autobiographical memory, the fate of semantic as well as episodic self-knowledge, and the presence of alter egos with their own funds of self-knowledge.

A small body of research exists on "subclinical" dissociation, as measured in "normal" individuals such as college students by questionnaires such as the DES. For example, a twin study suggested that 45% of the variance in DES "taxon" scores was attributable to the shared environment, and 55% to the nonshared environment, with no variance left over to be accounted for by genes (Waller & Ross 1997). High DES scores may reflect subclinical levels of dissociative disorder, which do not qualify, in terms of intensity, frequency, or duration for a formal clinical diagnosis. Alternatively, they may reflect an acquired diathesis factor that, when combined with adequate levels of stress, produce an acute episode of dissociative disorder. Although the DES is often used to screen individuals for possible dissociative disorder, there are no longitudinal studies testing the hypothesis that individuals with high scores on the DES are likely to develop a dissociative disorder later in life.

There is a small correlation between DES scores and self-reported trauma, including childhood physical and sexual abuse, in both student (e.g., DiTomasso & Routh 1993) and community samples (e.g., Mulder et al 1998). A meta-analysis of college-student studies by Rind et al. found that the association between self-reported dissociative symptoms and self-reported child sexual abuse is statistically significant but weak (r_u = .07; Rind et al 1998, Rind et al 2001). Interestingly, however, DePrince and Freyd found the difference between high and low dissociators is greater for low-betrayal experiences, such as natural disasters, than it is for high-betrayal experiences, such as incest – a finding seemingly incompatible with Freyd’s (Freyd 1996) betrayal-trauma theory of dissociation.

On the other hand, DES scores are also correlated, and usually more strongly, with fantasy proneness (e.g., Rauschenberg & Lynn 1995), false positives in recognition tests of memory (e.g., Merckelbach et al 2000a), the associative memory illusion (e.g., Winograd et al 1998), interrogative suggestibility (e.g., Merckelbach et al 2000b), imagination inflation (e.g., Paddock et al 1998), source-monitoring problems (e.g., Wilkinson & Hyman 1998), and the creation of pseudomemories (e.g., Hyman & Billings 1998). Setting aside the problems of inferring causation from correlation, such findings cast doubt on the link association between dissociation and self-reported trauma itself (Merckelbach & Muris 2001, Tillman et al 1994). In the subclinical as well as the clinical domain, the best evidence for any causal link will come from prospective studies.

Subjects who score high on the DES show increased levels of interference on a standard Stroop color-word task under typical selective-attention conditions, (DePrince & Freyd 1999, Freyd et al 1998), suggesting that individuals who have a tendency toward dissociation also have difficulties in the deployment of attention. These same investigators found a numerical tendency toward reduced interference under divided-attention conditions, suggesting that high-scoring subjects are particularly good at dividing attention (DePrince & Freyd 1999). However, the statistical reliability of this difference is rather weak – only one comparison out of four was statistically significant, and that only by virtue of a one-tailed test; accordingly, the finding warrants replication before too much should be made of it.

The difference between selective and divided attention may also mediate the performance of high-scoring subjects on directed-forgetting tasks (DePrince & Freyd 2001, DePrince & Freyd 2004). For example, DePrince and Freyd (2004) found that under divided-attention conditions high dissociators recalled fewer trauma-related words, and more neutral words, than low dissociators; there was no such interaction under selective-attention conditions. However, this difference occurred only for to-be-remembered items. There were no group differences in performance for to-be-forgotten items, for either item type under either condition. This null finding is puzzling, given the presumed ability of high dissociators to selectively forget trauma-related material. Again, such findings must be replicated and extended before too much theoretical weight is placed on them.

The dissociative disorders pose interesting philosophical and procedural challenges for the legal system (Hacking 1995, Humphrey & Dennett 1989, James 1998, Saks 1995). Defendants who are amnesic for the circumstances of a crime cannot assist in their own defense, and amnesic witnesses cannot offer testimony as to what may have happened to them. The fact that the amnesia is functional, and not linked to demonstrable brain insult, injury, or disease, raises the possibility of malingering. Memories ostensibly recovered through special techniques like hypnosis or the amytal interview warrant independent corroboration – although most states permit courtroom testimony based on hypnotically recovered memories, provided that the hypnotic procedure included certain safeguards to minimize the possibility of suggestion and maximize the likelihood that any contamination will be detected (Brown et al 1998, Laurence & Perry 1988, Scheflin & Shapiro 1989). Nor, of course, can dissociative symptoms be used to corroborate accusations of childhood physical and sexual abuse, on the theory that trauma and abuse causes dissociation. At best, that would be reasoning backwards (Rind 2003, Sbraga & O'Donohue 2003); but given that there is no good evidence for a traumatic etiology of DID or any other dissociative disorder, such a stance is simply inappropriate.

Defendants have occasionally raised the insanity defense based on a diagnosis of DID: typically, the claim is that an alter ego committed the crime. Sometimes this ploy succeeds, at least in so far as the defendant is committed to a mental hospital rather than jail, as in the famous case of Billy Milligan (Keyes 1981). Perhaps the most famous case, the Los Angeles "Hillside Strangler", generated a vigorous debate among expert witnesses (Allison 1984, Orne et al 1984, Watkins 1984); he was ultimately determined to be a case of malingering, and convicted, but escaped the death penalty. Even cases where a DID-based insanity defense is appropriate, the syndrome raises profound philosophical questions about personhood and personal responsibility: If one alter ego pleads guilty, can the other(s) be sentenced to jail? If one alter is insane, can the others be committed to a mental hospital – and can the others sign themselves out? Can a person with DID even enter into a valid legal contract, or consent to marry or have sex?

The appearance of the dissociative disorders as a separate category in DSM-III ratified their status as major forms of psychopathology. Looking towards DSM-V, some clinicians and researchers have proposed expansion of the category beyond the traditional quartet of amnesia, fugue, multiple personality, and depersonalization. For example, Dell has proposed expanding the list of features associated with DID to include hallucinations and Schneiderian first-rank symptoms (Dell 2001). On the other hand, if these symptoms are indeed present in many DID patients, it may mean little more than that they are actually misdiagnosed schizophrenics.

Perhaps the most prominent proposal for revision is to classify the dissociative disorders as forms of post-traumatic stress disorder (PTSD; Putnam 1985, Spiegel 1984) – or, perhaps, post-traumatic stress disorder as essentially dissociative in nature. This view is predicated on the assumption that the dissociative disorders are reactions to high levels of emotional stress: while the familiar symptomatology of PTSD entails vivid, intrusive memories of the stressful event, the dissociative disorders would represent a special case involving the absence of conscious recollection of the trauma. Alternatively, while the dissociative disorders entail a loss of conscious memory for trauma, more familiar form of PTSD would be reconstrued as entailing a loss of conscious control over traumatic memories. Such a proposal is interesting, not least because the memory problems displayed by high dissociators are paralleled by some individuals with PTSD (Bremner et al 2000, Clancy et al 1999, Clancy et al 2000, McNally et al 2004). But in view of the difficulties in demonstrating even a valid correlation between trauma and dissociation (Merckelbach & Muris 2001, Tillman et al 1994), much less a causal link, it is probably premature.

Another proposal is to move the conversion disorders from their present location in the somatoform disorders to the category of dissociative disorders (Kihlstrom 1992, Kihlstrom 1994). The basis for this proposal is that the dissociative disorders are fundamentally disorders of consciousness, not of memory or identity. Patients with dissociative disorder are not consciously aware of personal experiences and other aspects of self-knowledge that nonetheless remain available in memory, and implicitly influence their ongoing experience, thought, and action. Similarly, it appears that patients with conversion disorder, such as psychogenic or functional blindness and deafness, are not consciously aware of visual, auditory percepts, and show dissociations between explicit and implicit perception (e.g., Brady & Lind 1961, Bryant & McConkey 1989). The monosymptomatic pseudoneurological disorders of the sensory-motor system classified as conversion disorders have little in common with Briquet’s syndrome, histrionic (hysterical) personality disorder, hypochondriasis, and the other medically unexplained syndromes that make up the rest of the somatoform category (Kihlstrom & Canter Kihlstrom 1999). Accordingly, the dissociative disorder category might be expanded to include three subcategories: dissociative disorders of memory, including the syndromes currently classified as dissociative disorders; dissociative disorders of sensation and perception, including psychogenic (or functional) blindness, deafness, and tactile anesthesia; and dissociative disorders of the motor system, including psychogenic (functional) paralysis and aphonia. Pigs will fly first, because, as one authority on the somatoform disorders once informed me, "The conversion disorders are the jewel in the crown of the somatoform disorders, and we will never let them go". Nevertheless, the proposal has the advantage of using "dissociative" as a purely descriptive term, referring to a disruption in conscious awareness, and abandons both "dissociation" and "conversion" as psychodynamic labels for pathological processes or psychological defense mechanisms. Instead, "dissociative" would be a purely descriptive label referring to the divisions in consciousness, and dissociations between explicit and implicit memory and perception, that are at the heart of both the dissociative and conversion disorders.

Along somewhat similar lines, Nijenhuis and his colleagues have proposed a distinction between psychological dissociation, involving memory and identity, and "somatoform" dissociation, involving various bodily functions such as pain, arousal, anorexia-bulimia, and alternating responses to medication, alcohol, and allergens, as well as more typical conversion symptoms such as functional blindness, deafness, and anesthesia (NIjenhuis 2000). To this end, they have introduced various forms of a Somatoform Dissociation Questionnaire (SDQ; Nijenhuis et al 1996), as a somatic complement to the DES. The primary rationale for this proposal is that patients with DID and DDNOS also have physical complaints, and that these complaints can alternate depending on the ego state which is presently active (Nijenhuis et al 1998a, Nijenhuis et al 1999). In, addition, they note that many of the symptoms assessed by the SDQ have parallels in animal defensive reactions to predation and injury (Nijenhuis et al 1998b) – a point which fits nicely with the common (if unproven) assumption that the dissociative disorders are traumatic in origin. On the other hand, the distinction between psychological and somatoform forms of dissociation obscures the fundamental point that dissociative symptoms, reflecting disorders of conscious awareness, are always "psychological" in nature.

The revival of multiple personality disorder in the 1980s may have a parallel in the current upsurge of interest in depersonalization disorder (DPD; Simeon et al 1997, Simeon & Hollander 1993, Simeon et al 2003a, Steinberg 1991). Once considered relatively rare (Sierra & Berrios 2001), DPD is now being diagnosed with increasing frequency. Like their counterparts with DID, patients with DPD are likely to score high on the DES (Simeon et al 1998a), including the DES taxon (Simeon et al 2003b); a new Depersonalization Severity Scale (DSS; Simeon et al 2001c) has been developed specifically for the assessment of depersonalization disorder. Most of the current literature is descriptive in nature, although there have been a few forays into experimental (Guralnik et al 2000) and brain-imaging (Phillips et al 2001, Simeon et al 2000) studies. Depersonalization disorder is sometimes successfully treated with anxiolytic or antidepressant drugs (e.g., Simeon et al 1998b), but it is not clear whether the remission of depersonalization is a primary effect or secondary to the remission of anxiety or depression.

Of course, depersonalization is a well-known feature of a number of other syndromes, including anxiety disorder, obsessive-compulsive disorder, and depression -- including the phobic-anxiety-depersonalization syndrome classically described by Roth (Roth 1959); but in the case of DPD, depersonalization is the primary (and pervasive) symptom. Depersonalization is commonly observed in acute stress reactions (Cardena & Spiegel 1993), and a prominent theory links it to dysregulation along the hypothalamic-pituitary adrenal axis (Simeon et al 2001b). DPD has also been related to a history of childhood trauma (Simeon et al 2001a), but this etiological hypothesis is no more secure for DPD than it is for DID. Research on DPD, its origins, and its treatment is just in its infancy. However, the demonstrated linkage between acute stress and symptomatic depersonalization, combined with the persisting skepticism that surrounds DID, may lead clinicians and researchers interested in the both trauma and the dissociative disorders to become more interested in DPS, and less interested in DID, as the future unfolds.

More than 200 years after the first published case study of multiple personality, more than a century after the syndromes were formally recognized by mental health professionals, and fully 20 years since the current revival of interest in them began, the dissociative disorders continue to invite controversy – even more controversy, perhaps, than post-traumatic stress disorder. The case of Sybil, which arguably marks the onset of the MPD "epidemic" of the 1980s and 1990s, has now been thoroughly discredited (Borch-Jacobsen 1997, Borch-Jacobsen 2002, Rieber 1999). According to Spanos, DID has nothing to do with dissociation and awareness, but rather is "socially constructed... context bounded, goal-directed, social behavior geared to the expectations of significant others" (Spanos 1994, p. 143, Spanos 1996). Against a reassertion of the traditional model involving defenses against childhood trauma (Gleaves 1996) other "sociocognitive" theorists have proposed that DID is "a syndrome that consists of rule-governed and goal-directed experiences and displays of multiple role enactments that have been created, legitimized, and maintained by social reinforcement" (Lilienfeld et al 1999, p. 507, Lilienfeld & Lynn 2003). These social-psychological critiques have been echoed within both cultural criticism (Acocella 1999) and established psychiatry (McHugh 1995, Merskey 1992a, Merskey 1992b, Piper 1995, Piper 1997). Recent surveys suggest that more than half of American and Canadian psychiatrists harbor reservations about the validity of the diagnosis, and its inclusion in DSM (Lalonde et al 2001, Pope et al 1999).

On the other hand, the fact that dissociative symptomatology is embedded in the patient’s social context does not necessarily invalidate the diagnostic category itself. Even schizophrenia has a sociocultural overlay. Nor does the possibility that some - probably many, perhaps most -- recent cases of DID and other dissociative disorders are iatrogenic or misdiagnosed mean that the occasional genuine case should not be taken seriously. As rare as they may be, the dissociative disorders provide a unique perspective on fundamental questions concerning consciousness, identity, the self, and the unity of personality. As complex as they surely are, they deserve to be studied in a spirit of open inquiry that avoids both the excessive credulity of the enthusiast and the dismissal of the determined skeptic.

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