Dissociative Identity Disorder: Overview and Current Research
Research and Conclusions
Research trends currently focus on neurobiological and psychobiological factors unique to this disorder. For example, one study investigated the differences between alters who have access to traumatic memories and alters who suppress such information. The results indicate that different alters demonstrate differences in emotional, sensori-motor, cardiovascular, and regional cerebral blood flow in response to traumatic memories (Reinders, et al., 2006).
Another study sought to apply known findings about related disorders to DID. Because individuals diagnosed with disorders involving an etiology of stress (e.g., Post-Traumatic Sstress Disorder, Borderline Personality Disorder, Major Depressive Disorder with childhood trauma) have demonstrated a reduction in hippocampal volume, the authors of this study used magnetic resonance imaging and volumetric analyses to determine if any relationship also existed between DID and reduced hippocampal volume. Results indicated that the volume of the hippocampus of participants with DID was 19.2% smaller and the amygdala was 31.6% smaller than normal controls (Vermetten, Schmahl, Lindner, Loewenstein, & Bremner, 2006).Other studies have discovered findings that are relevant to the relationship between trauma and memory in DID. A case study investigating the neural correlates of switching between alters used functional magnetic resonance imaging to study changes in the brain during switching. The results indicated that during switching to the alternate personality, the client’s bilateral hippocampus was inhibited, as well as the right parahippocampal gyrus, right medial temporal lobe, globus pallidus, and substantia nigra. However, during transition to the host personality, the right hippocampus demonstrated evidence of increased activation, with no inhibition in any brain structures (Tsai, Condi, Wu, & Chang, 1999). These findings contribute to an understanding of amnesia between alters, since regions of the brain involved in memory are either inhibited or activated.
Other research supports the idea that alters develop to protect the host from unpleasant thoughts and memories involving trauma and abuse. Autobiographical memories may differ between alter personalities, allowing the host to retain positive memories while alters contain negative traumatic memories (Bryant, 2005). A study investigating directed forgetting found that “dissociative patients showed directed forgetting between states, but not within the same identity state” (p. 241). This study clarifies the mechanism and function of memory in various dissociative states and helps explain why trauma might result in the development of alters. Pushing threatening material out of consciousness can then be facilitated by a switch from one state of consciousness to another (Elzinga, Phaf, Ardon, & van Dyck, 2003).
While clinicians now understand more about DID than in the past, additional research is needed to clarify and further investigate the nature of DID. The research that has been completed on this disorder still leaves many questions unanswered. For example, future research should further examine risk factors, and clarify how genetic and environmental factors contribute to this disorder. More studies should determine the nature of the physical and psychological differences evident among alters, how they develop, and their significance. Psychopharmacological studies are needed to determine which medications work best, and why they are effective.
Multicultural research is necessary to determine how sociocultural factors affect the development and clinical presentation of DID. Additional research in this area will not only benefit individuals with DID and their families, but also the research and clinical psychology community as a whole. Gaining an improved understanding of Dissociative Identity Disorder involves more than the categorization of another mental disorder. Increased knowledge in this area also contributes to an improved understanding of the nature of consciousness and the mind-brain relationship, as well.
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