Alteration of corticothalamic perfusion ratios during a PTSD flashback.

We performed a single photon emission computed tomography (SPECT) study of patients with posttraumatic stress disorder (PTSD) by measuring changes in regional cerebral blood flow (rCBF) during provocation by combat stimuli. A single patient experienced an actual flashback following exposure to combat sounds, exhibiting tearfulness, diaphoresis, tachypnea, and severe agitation. Results from his SPECT study demonstrated a dramatically altered ratio of cortical to subcortical perfusion during the flashback but not during the control scan. This altered pattern, which showed a peak of activity in the thalamus, was not consistent with global rCBF changes induced by hyperventilation. The perfusion pattern during the patient's control scan was qualitatively indistinguishable from any of the SPECT scans obtained for the other patients. This single case suggests a possible role for corticothalamic dysfunction in flashbacks.