Arousal dissociates amygdala and hippocampal fear responses: Evidence fromsimultaneous fMRI and skin conductance recording

The experience and appraisal of threat is essential to human and animal sur vival. Lesion evidence suggests that the subjective experience of fear reli es upon amygdala-medial frontal activity (as well as autonomic arousal), wh ereas the factual context of threat stimuli depends upon hippocampal-latera l frontal activity. This amygdala-hippocampus dissociation has not previous ly been demonstrated in vivo. To explore this differentiation, we employed functional magnetic resonance imaging (fMRI) and simultaneous skin conducta nce response (SCR) measures of phasic arousal, while subjects viewed fearfu l versus neutral faces. fMRI activity was subaveraged according to whether or not the subject evoked an arousal SCR to each discrete face stimulus. Th e fMRI-with arousal and fMRI- without arousal data provided a distinct diff erentiation of amygdala and hippocampal networks. Amygdala-medial frontal a ctivity was observed only with SCRs, whereas hippocampus-lateral frontal ac tivity occurred only in the absence of SCRs. The findings provide direct ev idence for a dissociation between human amygdala and hippocampus networks i n the visceral experience versus declarative fact processing of fear. (C) 2 001 Academic Press.