Abstract
In patients with post-traumatic stress disorder (PTSD), re-experiencing the trauma is often induced by external cues in the environment. The cues, which were emotionally neutral for the patients before the traumatic event, become fearful ones after the event. This phenomenon is considered to be associated with fear conditioning. The paradigm was set up so that the emotionality changes in the patients with PTSD would be reproduced, and the regional cerebral blood flow (rCBF) measured with positron emission tomography (PET) was compared during exposure to the same stimuli before and after acquisition of fear conditioning. Ten healthy male subjects were asked to look at some emotionally neutral photos, then to watch a video with fearful content that also contained images similar to that presented in the photos, and afterwards to look at the photos again. Five of the 10 subjects felt that the object in the photos was more fearful after watching the video than before, and they were considered to have acquired fear conditioning. In those five subjects, the rCBF in the right amygdala and the left posterior cingulate gyrus after acquisition of fear conditioning significantly increased relative to the rCBF before conditioning. Thus, these regions seem to have a critical role in fear conditioning.
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