To better understand the pathophysiology and treatment of Posttraumatic Stress Disorder (PTSD), standard psychological testing, Rorschach Ink Blot testing, and neuroimaging using Single Photon Emission Computed Tomography (SPECT) were administered to subjects with PTSD prior to and following three sessions of Eye Movement Desensitization and Reprocessing (EMDR). Using this within-subject design, data from one of six subjects in our series is presented as a case report. Following EMDR, the subject experienced improvement in his level of distress, which correlated with decrements in PTSD and depressive symptomatology on psychological testing. Analysis of the Rorschach data corroborated these changes. Among other findings, the Hypervigilance Index went from positive to negative, indicating that the subject was spending less time scanning the environment for threats, and available ego resources also increased, as measured by the Experience Actual variable. Upon recall of the traumatic memory during SPECT scanning, two areas of the brain were hyperactive post-EMDR treatment relative to pretreatment: the anterior cingulate gyrus and the left frontal lobe. These changes were consistent with summed data from four out of six subjects in the ongoing study. An important implication of these findings is that successful treatment of PTSD does not reduce arousal at the limbic level, but instead, enhances the ability to differentiate real from imagined threat. The psychology and neurophysiology of PTSD are discussed in greater detail.