Functional MRI

Research Summaries

The Biological Psychology of Dissociative Identity Disorder Functional MRI of Personality Switches

	THE FOLLOWING IS A SUMMARY OF SOME KEY POINTS FROM: Tsai, Guochuan E. MD PhD, Condie, Donald MD, Wu, Ming-Ting MD, Chang, I-Wen BA. (1999). Functional magnetic resonance imaging of personality switches in a woman with dissociative identity disorder. Harvard Review of Psychiatry, 7, 119-122.

fMRI of Personality Switches

Studies have found decreased hippocampal volume in humans with post traumatic stress disorder resulting from childhood abuse. This is a study of one woman with comorbid diagnoses of PTSD and dissociative identity disorder.

Functional magnetic resonance imaging is an imaging technique that has both high temporal specificity and high spatial specificity. Because of this, it can be used for dynamic studies. Unlike PET scanning and single photon emission tomography, it does not expose the patient to ionizing radiation, so repeat studies do not increase patient risk.

For this study, the subject was a 47 year old, right handed, Caucasian woman with an extensive history of childhood physical and sexual abuse. This patient was able to volitionally switch between two alter personalities and to indicate when the switch was complete by pressing a button.

Volumetric studies showed a hippocampal volume "significantly smaller than reported values for normal female adults obtained by the same technique." During the process of switching from "native" to "alter" personalities, bilateral hippocampal inhibition was observed, with greater inhibition on the right side. Also inhibited were the right hippocampal and medial temporal regions and small regions of the substantia nigra and the globus pallidus. During the switch back from "alter" to "native", only the right hippocampus was activated. No other significant brain activity or inhibition was noted during either process of switching. A control was tested by having the patient experience guided imagery of an irrelevant personality (one invented by the testers), which produced no significant change in the fMRI scan.

This study suggests that personality switches in DID may be produced by alterations in hippocampal and temporal function. This is consistent with previous PET scan and EEG studies which have found changes in temporal region activity between different personalities in patients with DID. The authors speculate that reduced hippocampal volume in this patient may correspond to the reduced hippocampal activity during personality switches from "native" to "alter." The observation of hippocampal activation during the switch from "alter" to "native" also implies a hippocampus-mediated process. This process may be the neurophysiological basis for the therapeutic process of integration of personality states.

The hippocampus and associated medial temporal areas are responsible for declarative memory (conscious memory of specific events), and the nigrostriatal system is responsible for nondeclarative memory (gradual, incremental learning of association). This study proposes that both types of memory are involved in personality switches in persons with DID.

Limitations of this study include that the patient had dual diagnoses of PTSD and DID, so findings cannot be said to be exclusive to DID. Another limitation was that this patient was able to produce volitional switching between two specific personalities and to indicate when the switch was complete, which is unusual with DID patients early in their recovery. Because of this, findings may be specific to stage of reintegration and thus not generalizable. Also, "affectively charged volitional recall" is correlated with changes in hippocampal blood flow. fMRI studies have not been done on varying affective states in patients with DID. Another possibility is that the differences in brain activity reflect differences between personalities, rather than the procedure of switching.

Source:

Tsai, Guochuan E. MD PhD, Condie, Donald MD, Wu, Ming-Ting MD, Chang, I-Wen BA. (1999). Functional magnetic resonance imaging of personality switches in a woman with dissociative identity disorder. Harvard Review of Psychiatry, 7, 119-122.

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