In popular culture, Dissociation, and Dissociative Identity Disorder (previously known as Multiple Personality Disorder--MPD) is considered a very exotic, rare and enigmatic psychological phenomenon (11). It seems that, especially in the media and entertainment, multiple personality disorder is stigmatized by a number of quite florid and nearly hysterical symptoms. Clinically, however, Multiple Personality Disorder has been recognized for centuries and is currently estimated to exist in 1% of the general population (1,8), and as much as 7% of the population may have suffered from a dissociative disorder at some point in timem (9). Currently, DID (MPD) is most generally defined as a disturbance in the normally integrative functions of memory, identity, and consciousness (1,7,9). Most simply stated, MPD/DID is manifest as an inconsistent sense of self or "I" (7). Interestingly, it has been established that MPD/DID is actually one of many dissociative disorders and falls on a continuous spectrum of dissociation which ranges from normal/common dissociative episodes to "poly-fragmented" DID (1,9).
Researchers and clinicians believe that dissociation is a very common and naturally occurring defense mechanism, which results from early childhood trauma. Full blown DID or poly- fragmented DID (more than 100 personalities) is characteristically a result of severe, and prolonged occurrences of physical, sexual, or emotional abuse occurring before the age of 12 (and often before the age of 5) (1,8,11). In theory, the developmental processes behind DID are a result of resorting to mental 'escape' from the traumatic situation (8). This is essentially achieved when neither fleeing nor fighting is a viable defense option, which leads the individual to distance themselves from the incident to retain control (11). This distancing mechanism is characterized by detachment from the self or surroundings, excluding or loosing unwanted or unneeded feelings from awareness, and partial or total amnesia for the emotions and cognitions associated with the traumatic event.
Such distancing mechanisms are very powerful modes of defense and serve to escape the emotional and physical pain of the event by compartmentalizing the cognitions, sensory inputs, and behavioral enactment of the traumatic experience (12). These compartmentalized elements are essentially fragmented experiences, which fail to become integrated into an explicit narrative. In essence, this process allows the individual to separate the traumatic memories from ordinary consciousness to preserve some areas of healthy functioning (8,12). This entire process is referred to as dissociation.
Dissociation serves as a temporarily adaptive function, as it allows the individual to escape from the traumatic event while it is underway (9). However repeated reliance on dissociative defenses can lead to the inability to properly process information from past events and possibly future events into a narrative (explicit memory) form (12). It is theorized that the repeated use of dissociation can lead to the development of a series of separate entities or mental states which may eventually take on an entity or identity of their own (8). These entities may become internal "personality states" which reflect different states of consciousness (8). Furthermore, these entities or personality states are frequently created to contain or house the fragmented memories related to different traumatic incidents (12).
A multiple personality or DI will frequently and permanently isolate aspects of their "fragmented" traumatic experience into similarly "fragmented" alter egos. These created personalities are then likely to serve as mechanisms for coping with situations and events dealing with one particular aspect of the traumatic experience-- i.e.- when the individual feels rage, an angry personality is conjured to display this temperament and deal with these emotional issues. This loss of continuity in memory and consciousness (in the form of "alter egos") leads to an inability to establish a unified control system (9). In a sense, these personalities are themselves fragments and represent many incomplete selves, instead of a proliferation of selves (9). The development of "alter egos" can become extensive enough so that it is not uncommon to witness alters which display differences in gender, age, religion, handedness, handwriting, voice and even cerebral blood flow and brain electrical activity (9,14).
Although this theoretical framework provides a logical explanation for the development of DID/MPD, it does not provide any insights into the physiological, biological and neurological underpinnings of the phenomenon. There are many co-occurring symptoms and disorders that are associated with DID/MPD that first implicated the prominent neurobiophsysiological abnormalities underlying the pathology. Firstly, it has been consistently observed in clinical settings that MPD patients also suffer from recurrent depression, anxiety, panic, phobias, anger, rage, low self-esteem, substance abuse, eating disorders (bulimia, anorexia, compulsive overeating), sexual dysfunction, time loss, memory gaps, sense of unreality, flashbacks, intrusive thoughts and images of trauma, hypervigilance, and sleep disturbances (1,13). Furthermore, it has been documented that 80-100% of people diagnosed with DID also have a secondary diagnosis of PTSD (posttraumatic stress disorder).
Some organic causes of dissociation are both known and suspected. For example, many experts believe that temporal lobe epilepsy may lead to a dissociative disorder. Other physical conditions which can lead to some level of dissociation are sleep loss, sensory deprivation, strokes, encephalitis, and Alzheimer's disease. Even more interesting, the unity of self can be disrupted when the corpus callosum (the commissure that joins the two hemispheres of the cerebral cortex) is severed (9). This particular instance of disruption of self has been historically described as a "Jekyll and Hyde" type experience where the left and right hemispheres act as two independent and seemingly different entities (4,5,6). It has been these findings that have ultimately spurred research on the possible neurobiological etiology of MPD (3).
Given the prevalence of the concurrence of PTSD and MPD, it seems appropriate to briefly explore the possible neurobiological ramifications of PTSD, and how they may serve to segue into full dissociative identity disorder. It seems that the most salient pathogenic mechanism related to PTSD is the previously mentioned fragmentation of trauma related events. Consistent research has displayed how declarative or explicit memory functioning is seriously effected by patients suffering from PTSD (12). Characteristically, PTSD patients will recall, or reference the traumatic event only in the form of implicit or perceptual information, such as visual images, olfactory, auditory, or kinesthetic sensations, or intense waves of feelings (12). Recent neuroimaging studies have supported this clinical observation. During provocation of traumatic memories, it has been reported that activity in Broca's area (a portion of the central nervous system that is involved in the transformation of subjective experience into speech) is markedly suppressed (2). Simultaneously, the areas in the right hemisphere that are thought to process visual images and intense emotions were highly activated (2) .
These imaging studies seem to support the theoretical claims of the sequestering of fragmented information. It would seem that the neural memory traces that hold the specifics of the trauma (imagery, sensory input, sound, smell, etc.) are isolated from one another. They are in essence compartmentalized. This implies that in fact small portions of the brain are isolated or compartmentalized. The only way in which these memories could retain their fragmented and isolated status is if the areas of the brain that housed and retained the information were not connected to one another to form a coherent whole.
As it is known, one area of the brain cannot integrate its information with another area unless there is a means of communication. In turn, the communication between neurons necessary for this type of integration of information cannot occur unless the neural traces are physically connected (i.e.--the law of physical contiguity). The mere nature of trauma seems to lend itself to the physical isolation of neural networks within the brain. It could be imagined how repeated and conditioned compartmentalization could lead to deeply rooted and plastic changes in neural circuitry. As such, it can be seen how the isolation of neural traces could in and of itself lead to the propensity of split brain/MPD phenomena.
The traumatic and stressful nature of the experience also plays an important role in the mediation of neurochemicals, hormones, and modulatory substances in the body. Uncontrollable and extreme stress which has been experience for long periods of time in both PTSD and MPD patients has lead researchers to question the chronic effects these chemical substances released during stressful episodes. It has been determined that stress is related to the increased production of several neurotransmitters, neuropeptides, including norepinephrine, corticotropin releasing factor, as well as cortisol, opiates, dopamine and serotonin (2). Although the marked increase the release of these substances in beneficial for short-term survival, the long term or chronic effects of these substances are detrimental (2). Most generally, chronic stress related substance secretion causes the death of neurons.
In many cases, cortico- steroids released chronically and continuously due to frequent exposure to stressful events can act as neurotoxins, causing the death of neurons specifically in the hippocampus. Interestingly, it is the hippocampus that serves to unify memory elements from diverse neocortical areas (2). In one study, patients who had suffered from abuse displayed 12% smaller hippocampal volume as compared to matched controls (2). This abnormal function of the hippocampus caused by degeneration may further account for the fragmentation of traumatic memories, as well as the clinical phenomenon related to MPD of dissociative amnesia. The amnesic episodes may further serve as a barrier between certain subsystems or isolated neural networks previously mentioned. In the extreme case of MPD, these separations may be sufficiently pronounced and contain enough disparate information so that these subsystems or isolated neural networks could possibly take on a 'personality' of their own. But how does this occur?
Firstly, it seems important to consider the developmentally vulnerable age at which the trauma is experienced. In most common approaches to development, it is assumed that the evolution of the 'self', 'I', or unitary conscious state is in fact dynamic. Particularly in early childhood, it is conventionally assumed that the idea of the self or I is underdeveloped and quite malleable. Especially in the western traditions, the unitary conscious self is very much a learned phenomenon, which requires a period of experiential development. This seems to coincide with the knowledge that the neural structure of the developing brain is most fluid and subject to growth in the earlier stages of life. As such, the effects of traumatic events in childhood are most probably neurobiologically detrimental enough to induce such extreme dissociative patterns that later constitute MPD. In this sense, the dissociative phenomenon is proliferated by the neurobiological susceptibility of the developing brain.
Furthermore, the fact that the child has not developed an entrenched 'I' function would make the brain much more susceptible to fragmentation. With the continual compartmentalization of emotional, cognitive, and behavioral states, the I-function is not given the chance to form into a unitary whole. In order to make sense of scattered and disjoint experiences, it seems that the brain has no choice but to create separate I-functions which are relevant to each isolated neuronal trace or 'island'. This could also explain why PTSD and traumatic events experienced in adulthood do not normally cause MPD. This is probably due to the fact that the I-function or reference point is so rigidly intact, that it is more probable that the traumatic memories become continually more intrusive until they are integrated into the already entrenched schema. In other words, with no preexisting structural reference, stress induced states are more likely to result in a more disorganized or fragmentary state (entropy).
The dissociation of the I function could be viewed in another way as well. The I-function serves as a reference point to the environment and provides the capability to imagine oneself as an object that can be moved from one place to another. With this in mind, an alternate or additional etiology for MPD could be constructed. It could be proposed that the isolated neural components could potentially house many different perspectives or 'ideas' of a reference point. With disjoint memories, it seems that one could have many different reference points at the same time, since the emotions and cognitions are not actually recognized as being a part of the same point in time and space. Hence if there are different perceived reference points at any given time, there could be different 'I' functions as well.
Given the information presented, it would seem that MPD could be developed from a mixture of developmental susceptibility as well as detriments of chronic stress. It is clear that MPD is a product of structural deficits and degeneration as well as adaptive mechanisms. Its seems that the adaptive mechanism is first employed in a healthy manner, to avoid distress, but is then exacerbated by the influences of chronic stress. This chronic stress seems to encourage the original dissociative behavior by providing neural deficits as well. In a sense, the entire process lends itself to a positive feedback loop, where an initially adaptive mechanism becomes maladaptive due to extensive conditioning and entrenchment of chemical abnormalities as well as neural degeneration.
To impose some sort of logic to the increasing disorganization, the brain seems to make the most of its intrinsic variability (adaptability) by associating fragmented neural patterns to differing reference points or I-functions. In this instance, the brain's mechanisms are similar to those that occur in dreaming. However, instead of trying to make sense of random brain stem signals as in the Dream State, in MPD, the brain tries to place meaning and context to the disjoint memories. This results in the most logical choice which would be to assign reference points/I-functions to each fragment, and then use these reference points to both adapt to and deal with past and future traumatic situations.
2)The Neurobiology of Traumatic Stress: Relevance to Posttraumatic Stress Disorder and the So-called "False Memory Syndromes, By J. Douglas Bremner, M.D.
3)Article: The Mind Body Connection, By Patricia D. McClendon
4)Splitting the Human Brain, By Paul Pietsch
5)Split Brain Paper with Funnel and Gazzaniga
6)Unity of Consciousness
7)Multiplicity and Victimization, By Patricia D. McClendon
8)Dissociative identity Disorder (Multiple Personality Disorder)
9)Dissociation and Dissociative Disorders
12)Dissociation and the Fragmentary Nature of Traumatic Memories: Overview and Exploratory Study, By Bessel A. van r Kolk and Rita Fisler
13)The Effects of DID on Children of Trauma Survivors, By Esther Giller
Additional Interesting Articles:
11)Questions About Multiple Personality
14)Child Abuse and Multiple Personality Disorder, By Philip M. Coons, M.D.
15)ISSD-Guidelines for Treatment
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