Effect of repeated visual traumatic stimuli on the event related P3 brain potential in post-traumatic stress disorder

Post-Traumatic Stress Disorder (PTSD) patients are characterized by a hypersensitivity to traumatic stimuli which may be expressed as an automatic and involuntary cognitive response. Electrophysiologically this can be recorded as an augmented visual P3 (P300) event related potential (ERP). This study examined P3 changes in response to repeated traumatic pictorial stimuli presented in the form of a visual discrimination oddball paradigm to 40 Israeli combat veterans with and without PTSD. Subjects were asked to press a button when target stimuli (domestic animal pictures) appeared, and to ignore all non-target stimuli (irrelevant pictures of furnishings/flowers and traumatic combat related pictures). On average, P3 in response to combat related pictures was earlier and approximately 5 times greater in amplitude for the PTSD patients as compared to the controls. Repeated combat related pictures stimuli presentation resulted in a rapid and appreciable P3 amplitude reduction and latency prolongation. This effect was not observed for the target stimuli. These findings suggesr that a gradually reduced amount of attentional resource is required and allocated to the processing of repeated CRP stimuli. This may occur as a consequence of the activation of an inhibitory mechanism related to the cognitive processing of traumatic stimuli.