Given the infancy of the field of neurobiology, the physiological foundations of all psychotherapies are currently unknown, and therefore, all neurobiological models of psychotherapy are speculative. Testing of hypotheses about EMDR’s neurological mechanisms awaits the development of advanced brain imaging techniques. Hypotheses concerning EMDR’s neurobiological mechanisms are, at this time, purely speculative.
Rauch, van der Kolk, and colleagues (1996) conducted positron emission studies of patients with PTSD in which they were exposed to vivid, detailed narratives which they had written about their own traumatic experiences. Patients showed heightened activity only in the right hemisphere, in the areas most involved in emotional arousal, and heightened activity on the right visual cortex, reflecting the flashbacks reported by these patients. Perhaps most significantly, Broca’s area - the part of the left hemisphere responsible for translating personal experiences into communicable language -“turned off”. These findings indicate that PTSD symptoms are reflected in actual changes in brain activity.
Case study research by van der Kolk and colleagues (Levin, Lazrove, & van der Kolk, 1999; van der Kolk, Burbridge, & Suzuki, 1997; Zoler, 1998) has provided some preliminary evidence that changes in brain activation patterns may follow effective treatment. SPECT scans were administered pre and post-EMDR for 6 PTSD subjects who each received 3 EMDR sessions. The Zoler article has photos of pre and post SPECT scans. Findings indicated metabolic changes after EMDR in two specific brain regions. First, there was an increase in bilateral activity of the anterior cyngulate. This area moderates the experience of real versus perceived threat, indicating that after EMDR, PTSD sufferers may no longer be hypervigilant. Second, there appeared to be an increase in pre-frontal lobe metabolism. An increase in frontal lobe functioning may indicate improvement in the ability to make sense of incoming sensory stimulation. Levin et al. concluded that EMDR appeared to facilitate information processing. Because there was no control group, there is no evidence that these effects were unique to EMDR; effective treatment of any kind may produce similar results.
Daniel Amen (2001) has been taking pre and post SPECT scans of his patients. He has used EMDR with PTSD patients, and reported a decrease in anterior cingulate, basal ganglia and deep limbic activity. The 12th chapter of Shapiro’s (2001) text details some related recent neurological research and explains the possible relevance of these findings to EMDR. Also of interest is an article by Stickgold (2002), a sleep researcher, who has developed a theory to explain the effects of EMDR’s alternating, bilateral stimulation which forces the client to constantly shift his or her attention across the midline. He proposed that REM-like neurobiological mechanisms are facilitated by this shifting attention, resulting in the activation of episodic memories, and their integration into cortical semantic memory. Independent research by Christman and Garvey (2000) provides some support for this theory. They determined that alternating leftward and rightward eye movements produced a beneficial effect for episodic, but not semantic, retrieval memory tasks.