The Emerging Psychobiology of Trauma-Related
Dissociation and Dissociative Disorders
Ellert R.S. Nijenhuis, Onno van der Hart, and Kathy Steele
Mental dissociation is an intriguing and complex phenomenon that has been studied clinically and theoretically for more than 150 years. Major empirical studies have been conducted during the last two decades. For example, these studies have established that the prevalence rates of the DSM-IV dissociative disorders (APA, 1994) are considerable among psychiatric inpatients, with an overall prevalence among nine studies of 18.9% for dissociative disorders in general, and 4.4% for dissociative identity disorder (DID; Friedl et al., 2000). Only in recent years has dissociation begun to receive attention from a combined psychological and biological perspective.
The study of dissociation has been impeded by several factors. First, conceptual confusion and controversy exist regarding the nature of this phenomenon. For example, dissociation is described as a process, as various symptoms, as mental structure, as psychological defense, and as a deficit in integrative capacity. In addition, it is confused with retraction of the field of consciousness (that which is within awareness at a given time) such as absorption, daydreaming, and states of inattention. Although negative dissociative symptoms such as amnesia are acknowledged, positive ones, such as intrusive re-experiences of trauma, are often not understood as dissociative in nature.
Second, diagnostic and aetiological issues are far from resolved in psychiatric disorders in which dissociation is an essential feature. For example, it is debatable that the DSM-IV category of dissociative disorders encompasses the actual range of dissociative disorders. As discussed below, although post-traumatic stress disorder (PTSD) is classified as an anxiety disorder, there are arguments to regard it as a dissociative disorder (e.g., Nijenhuis et al., 2002b). And the ICD-10, for instance, includes dissociative disorders of movement and sensations that are defined in the DSM-IV as conversion disorders. It has been theoretically argued (Kihlstrom, 1994; Nemiah, 1991; Nijenhuis and Van der Hart, 1999a) and empirically documented (Nijenhuis, 1999) that conversion symptoms are dissociative in nature. Conversion is better conceptualized as somatoform dissociation in that the symptoms of concern are at least equally characteristic of DSM-IV dissociative disorders as dissociative symptoms that manifest in psychological variables, i.e., so-called psychoform dissociation (Van der Hart et al., 2000). Moreover, somatoform dissociation correlates very strongly with psychoform dissociation (Nijenhuis, 1999; Nijenhuis et al., 1996, 1997, 1999b; Sar et al., 2000; Waller et al., 2000), and evidence for the hypothesis that psychological conflicts can be converted into physical symptoms, and thus reduce mental strain, is lacking.
Although the DSM-IV dissociative disorders have received wide acceptance, there exists a vocal minority of clinicians and researchers who express their scepticism about the validity of the most complex dissociative disorder, DID (Spanos and Burgess, 1994). As we will discuss in more detail below, patients with DID have severe somatoform and psychoform dissociative symptoms that relate to the existence of two or more self-aware dissociative systems, i.e., dissociative systems of ideas and functions that involve a sense of self. However, sceptics doubt that dissociative personalities are genuine phenomena. Simulated or factitious cases of DID certainly exist (Draijer and Boon, 1999) along with genuine cases, and the psychobiological differences between genuine and false positive cases of DID are a fruitful area of research. Some authors have also questioned whether chronic childhood traumatization is an aetiological base for DID and other dissociative disorders, but research has converged to indicate traumatic events are a key element in the psychopathology of dissociation and dissociative disorders. Retrospective (e.g., Boon and Draijer, 1993; Coons, 1994; Kluft, 1995; Lewis et al., 1997; Nijenhuis et al., 1998b) and prospective studies (Ogawa et al., 1997) – some of which have provided external corroboration for reported trauma–have confirmed the clinical observation that dissociative symptoms and disorders are associated with reported and factual traumatization. Studies have also demonstrated discrete and long-lasting alterations in neurobiological systems in relation to trauma and dissociation, which will be discussed below.
The current chapter focuses on dissociation related to traumatization. The first aim of the chapter is to reduce confusion about the concept of dissociation. Next, possible neuroendocrine parameters of dissociation and key brain structures that seem to be involved in the phenomenon are discussed. Several neurobiological models of dissociation will be reviewed, including Putnam's discrete behavioural states model (Putnam, 1997). Finally, the theory of structural dissociation will be presented (Nijenhuis and Van der Hart, 1999b; Van der Hart et al., 1998; Nijenhuis et al., 2002b; Steele et al., 2001), along with supporting evidence. The theory attempts to explain trauma-related dissociation as it manifests in disorders ranging from simple PTSD to DID, and serves an important heuristic function with regard to the emerging psychobiological study of trauma-related dissociation.
Dissociative symptoms are often misunderstood as indicators of other disorders or problems. Thus, it is quite common for dissociative disorder patients to hear internal voices (easily confused with psychosis); to experience disorientation to time, place and person during intrusive re-experiences (confused with intoxication, delirium, delusions, hallucinations, and psychosis); to have