PET Scan

Research Summaries

The Biological Psychology of Dissociative Identity Disorder One Brain, Two Selves: PET Scan

	THE FOLLOWING IS A SUMMARY OF SOME KEY POINTS FROM: *Reinders, A.A.T.S., Nijenhuis, E.R.S., Paans, A.M.J., Korf, J., Willemsen, A.T.M., and den Boer, J.A. (2003). One brain, two selves. Neuroimage, 20, 2119-2125.*

PET Scan Study

Dissociative identity disorder is characterized by one person experiencing more than one autonomous experience of self, each with its own "behavioral characteristics, sensations, perceptions, memories, bodily functions and autobiographical sense of self." This experience is facilitated by a childhood history of repeated, severe trauma. DID patients usually experience "traumatic" and "neutral" personality states, TPS and NPS respectively, with TPS having access to traumatic memories and NPS having either amnesia for the traumatic memories or reacting as if the traumatic events did not happen to them. These personality states alternate control of the patient's behavior and consciousness.

This study used positron emission tomography to study four different conditions: exposure of one NPS to neutral and traumatic memory scripts, and exposure of one TPS to the same neutral and traumatic memory scripts. The goal was to discover whether different brain activation patterns could be determined for the different conditions.

The study subjects were 11 female DID patients, ages 27-48 years, who had the ability to volitionally switch between one of their NPS and one of their TPS. The TPS had at least one traumatic memory to which it had an emotional response, while the NPS either claimed amnesia for the event or considered the traumatic event as not having happened to it.

The therapist of each individual subject read a script of 120 seconds in a neutral voice, which was audiotape recorded. One neutral event and one traumatic event specific to the patient were read to each of one NPS and one TPS. Only the event was recounted, not the consequences or effects of the event on the patient. The memories were recounted in third person singular.

PET scans and autonomic responses were recorded for each condition, and subjects were debriefed after each condition on their response on a 10-point scale of fear, sorrow, sadness, anger, shame and disgust, as well as 10 sensorimotor responses: visual, kinesthetic, auditory, olfactory, gustatory, pain, physical numbness, body stiffening, paralysis and restlessness.

The hypothesis was that the NPS would experience the traumatic memory as not pertaining to itself while the TPS would be cognizant that the memory was its own.

In this study, the trauma script produced "a network of deactivated brain areas including the right medial prefrontal cortex, the bilateral middle frontal gyrus, the visual association and the bilateral parietal integration areas." This finding was consistent with other functional imaging studies of normal subjects in self versus nonself episodic memory retrieval, confirming that the NPS viewed the traumatic event as not related to itself. This pattern of inactivation indicates the "inability of the NPS to integrate visual and somatosensory information", which thwarts emotional processing. This "blocking" is the defense system of DID patients which facilitates their functioning in life. The disorder of parietal and occipital blood flow in the NPS reflects the decreased level of somatosensory consciousness and integration by inhibition of the (re)activation of these areas, indicating clinical depersonalization of the NPS. In contrast, the TPS showed activation in the brain areas related to emotional and behavioral reaction to pain when read the trauma script. These differences in brain activation indicate emotional and behavioral dissociation in patients with DID. The brain areas involved are those related to conscious awareness, and demonstrate the "emergence of conscious (TPS-trauma script) versus unconscious (NPS-trauma script) experience in the neural network."

This study demonstrates that DID patients have different access to affective memories depending on personality state, and so have different experiences of self. The authors conclude: "Our results indicate the possibility of one human brain to generate at least two distinct states of self-awareness, each with its own access to autobiographical trauma-related memory, with explicit roles for the medial prefrontal cortex and the posterior associative cortices in the representation of these different states of consciousness." (emphasis added)

Source:

Reinders, A.A.T.S., Nijenhuis, E.R.S., Paans, A.M.J., Korf, J., Willemsen, A.T.M., and den Boer, J.A. (2003). One brain, two selves. Neuroimage, 20, 2119-2125.

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