Human amygdala activation during conditioned fear acquisition and extinction: a mixed-trial fMRI study

Echoplanar functional magnetic resonance imaging (fMRI) was used in normal human subjects to investigate the role of the amygdala in conditioned fear acquisition and extinction. A simple discrimination procedure was employed in which activation to a visual cue predicting shock (CS+) was compared with activation to another cue presented alone (CS-). CS+ and CS- trial types were intermixed in a pseudorandom order. Functional images were acquired with an asymmetric spin echo pulse sequence from three coronal slices centered on the amygdala. Activation of the amygdala/periamygdaloid cortex was observed during conditioned fear acquisition and extinction. The extent of activation during acquisition was significantly correlated with autonomic indices of conditioning in individual subjects. Consistent with a recent electrophysiological recording study in the rat (Quirk et al., 1997), the profile of the amygdala response was temporally graded, although this dynamic was only statistically reliable during extinction. These results provide further evidence for the conservation of amygdala function across species and implicate an amygdalar contribution to both acquisition and extinction processes during associative emotional learning tasks.