Time course of amygdala activation during aversive conditioning depends on attention.

The time course of amygdala activation during aversive conditioning is a matter of debate. While some researchers reported rapid habituation, others found stable or no amygdalar responses to conditioned stimuli at all. In the present event-related fMRI study, we investigated whether the activity of the amygdala during aversive conditioning depends on attentional conditions. Subjects underwent aversive delay conditioning by pairing an electrical shock (unconditioned aversive stimulus) with a visual conditioned stimulus (CS+). For each singular presentation of the CS+ or a nonconditioned visual stimulus (CS-), subjects attended in random order to features that either differed between both stimuli (identification task) or that did not differ (distraction task). For the identification task trials, increased responses of the left amygdala to CS+ versus CS- were rapidly established but absent at the end of the conditioning trials. In contrast, under the distraction condition, amygdala activation to CS+ versus CS- was present during the late but not the early phase of conditioning. The results suggest that the time course of amygdala activity during aversive associative learning is strongly modulated by an interaction of attention and time.