SYNAPTIC TRANSMISSION AND PLASTICITY IN THE AMYGDALA - AN EMERGING PHYSIOLOGY OF FEAR CONDITIONING CIRCUITS

Numerous studies in both rats and humans indicate the importance of th e amygdala in the acquisition and expression of learned fear. The iden tification of the amygdala as an essential neural substrate for fear c onditioning has permitted neurophysiological examinations of synaptic processes in the amygdala that may mediate fear conditioning. One cand idate cellular mechanism for fear conditioning is long-term potentiati on (LTP), an enduring increase in synaptic transmission induced by hig h-frequency stimulation of excitatory afferents. At present, the mecha nisms underlying the induction and expression of amygdaloid LTP are on ly beginning to be understood, and probably involve both the N-methyl- D-aspartate (NMDA) and lpha-amino3-hydroxy-5-methyl-4-isoxazolepropion ate (AMPA) subclasses of glutamate receptors. This article will examin e recent studies of synaptic transmission and plasticity in the amygda la in an effort to understand the relationships of these processes to aversive learning and memory.