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Abnormal stimulus-response intensity functions in posttraumatic stress disorder: an electrophysiological
Jeffrey David Lewine1, Robert J Thoma, Sherri L Provencal
1Departments of Psychology and Psychiatry, University of New Mexico, Albuquerque, NM, USA. jeffreylewine@aol.com
Objective:
The purpose of this study was to explore the relationship between combat-related posttraumatic stress disorder (PTSD) and specific augmentation versus reduction patterns for the N100 and P200 components of auditory event-related potentials evoked by tones of increasing intensity.
Method:
Event-related potentials of subjects with PTSD (N=36), subjects with no psychopathology (N=20), subjects with major depression but no PTSD (N=10), and subjects with a history of chronic alcohol abuse but no PTSD (N=8) were recorded. Brain responses were evoked by a 2000-Hz tone presented in intensity blocks of 65, 72.5, 80, 87.5, and 95 dB (SPL).
Results:
Evoked data from five PTSD subjects were of poor quality and excluded from further analyses. For all but one subject with no psychopathology and for all subjects with a history of alcohol abuse or major depression (but no PTSD), the Cz amplitude of the P200 response component showed augmentation as a nearly linear function of tone intensity. As a group, subjects with PTSD showed no such increase in P200 response magnitude. Examination of the data from individual subjects with PTSD showed that 42% exhibited augmentation patterns similar to those seen for subjects in the comparison groups. However, 58% showed evidence of P200 reduction, with the response to the loudest tone being smaller than responses to tones of intermediate intensity.
Conclusions:
The data suggest that there is a significant subgroup of patients with combat-related PTSD who enter into a state of protective inhibition at relatively low stimulus intensities. It is hypothesized that this is an appropriate adaptive mechanism for these subjects rather than an indication of a core neurobiological abnormality.