Evoked potential correlates of Post-Traumatic Stress Disorder in refugees with history of exposure to torture

The presence and magnitude of information processing deviations associated with Post-Traumatic Stress Disorder (PTSD) are far from being well-characterized. In this study we assessed the auditory and visually evoked cerebral responses in a group of Iraqi refugees who were exposed to torture and developed PTSD (N = 20), Iraqi refugees who had been exposed to similar trauma but did not develop PTSD (N = 20), and non-traumatized controls matched for age, gender, and ethnicity (N = 20). We utilized two paired-stimulus paradigms in auditory and visual sensory modalities, respectively. We found significantly smaller amplitudes of both the auditory P50 and the visual N75 responses in PTSD patients compared to controls, reflecting decreased response to simple sensory input during a relatively early phase of information processing (interval 50-75 ms post stimulus). In addition, deficient suppression of the P50/N75 response to repeating stimuli at this early stage in both modalities is indicative of difficulty in filtering out irrelevant sensory input. Among associations between electrophysiological and clinical measures, a significant positive correlation was found between dissociation score and P50 S1 amplitudes (p = 0.024), as well as stronger auditory P50 gating correlated with higher quality-of-life index scores (p = 0.013). In addition, smaller amplitudes of N150 visual evoked response to S1 showed a significant association with higher avoidance scores (p = 0.015). The results of this study highlight the importance of early automatic auditory and visual evoked responses in probing the information processing and neural mechanisms underlying symptomatology in PTSD.