Trauma may result in permanent neuronal changes that have a negative effect on learning, habituation, and stimulus discrimination. The effects of some of these neuronal changes do not depend on actual exposure to reminders of the trauma for expression. The abnormal startle response (ASR) characteristic of PTSD is one example of this phenomenon. Several studies have demonstrated abnormalities in habituation to the
ASR in PTSD (e.g., Ornitz and Pynoos, 1989). Interestingly, people who previously met the criteria for PTSD, but no longer do so now, continue to show failure of habituation of the ASR (van der Kolk et al., unpublished data; Pitman et al., unpublished data).
The failure to habituate to acoustic startle suggests that traumatized people have difficulty evaluating sensory stimuli and mobilizing appropriate levels of physiological arousal. Thus, the problems that people with PTSD have with properly integrating memories of the trauma, tending to get mired in a continuous reliving of the past, is mirrored physiologically in the misinterpretation of innocuous stimuli as potential threats. To compensate, they tend to shut down. However, the price for shutting down is decreased involvement in ordinary, everyday life.
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