title: Abnormal stimulus-response intensity functions in posttraumatic stress disorder: an electrophysiological investigation.
abstract: 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.
  
  
  METHODS
  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.
mesh_terms: D000161:Acoustic Stimulation; D001303:Auditory Cortex / Q000503:physiopathology; D001921:Brain / Q000503:physiopathology; D003130:Combat Disorders / Q000175:diagnosis / Q000503:physiopathology; D003866:Depressive Disorder / Q000175:diagnosis / Q000503:physiopathology; D004569:Electroencephalography / Q000706:statistics & numerical data*; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009433:Neural Inhibition / Q000502:physiology; D013313:Stress Disorders, Post-Traumatic / Q000175:diagnosis* / Q000503:physiopathology; D019966:Substance-Related Disorders / Q000175:diagnosis / Q000503:physiopathology