Unilateral storage of fear memories by the amygdala.

Pavlovian fear conditioning is an associative learning task in which subjects are trained to respond defensively to a neutral conditioned stimulus (CS) by pairing it with an aversive unconditioned stimulus (US). This type of learning depends critically on the amygdala, and evidence suggests that synaptic plasticity within the lateral nucleus of the amygdala (LA) may be responsible for storing memories of the CS-US association. In the present study, we trained rats to fear an auditory CS by pairing it with a shock US delivered to one eyelid.