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Ask the Mental Health Expert Archives 2001-2004

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Multiple Personality Disorders

Q. I am doing research on Multiple Personality Disorders (DID) and cannot find any information regarding how the brain reacts. Which part of the brain causes a person to block out the past and become these other personalities? Can you give me some information of the effects of DID on the brain, rather than the causes?

A. You are probably having difficulty because the research you are describing has barely begun! First of all, the whole concept of Multiple Personality Disorder (now classified as Dissociative Identity Disorder, or DID) is still very controversial--some mental health professionals still doubt that real DID exists. (My own view is that it is extremely rare, but is a real condition). Second, the number of subjects studied in the detailed way your question would require is extremely small. Third, it is often very hard to tell what is cause and what is effect, when it comes to studying the brain.

For example, if you found a patient with DID, and carefully studied that person's brain electrical activity, brain chemistry, etc., how would you determine if any abnormalities were the cause, or the result, of DID? That would take a very large sample size and a large control group. All these caveats aside, there are a few intriguing findings related to DID and brain activity. For example, Flor-Henry and colleagues (Int J Psychophysiol 1990 Dec;10(2):151-61) described two cases of multiple personality that were studied neurophysiologically and neuropsychologically. Bilateral frontal (Right greater than Left) and left temporal dysfunction was present in both cases. Both cases, upon EEG analysis, were in a state of relative left hemisphere activation, across all cerebral regions and task conditions.

The one case who was cured with hypnotherapy, showed, after recovery, normal left hemisphere functions neuropsychologically but remained in a state of relative left hemisphere activation electrophysiologically (on EEG). Both patients were unmedicated throughout. The authors presented a neurophysiological model to account for these findings--but I think it is far from clear how generalizable these results are, or whether they point to a cause or effect of DID.

A study by Mathew et al (Am J Psychiatry 1985 Apr;142(4):504-5) examined cerebral blood flow in a patient with multiple personality during two different personalities. The same patient was also assessed after recovery, as were three control subjects. Personality change was associated with no significant alterations in cerebral blood flow except right temporal hyperperfusion. It's hard, once again, to know what to conclude from these findings, but I think that the temporal lobes have been prime suspects in much of the neurological literature on DID.

For a review of this complex topic, see Miller & Triggiano, Am J Clin Hypn 1992 Jul;35(1):47-61. You should also see the paper by Hughes et al (in Clin Electroencephalogr 1990 Oct;21(4):200-9) which tries to correlate EEG patterns with individual sub-personalities in DID patients.

April 2002

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