Cortical-subcortical innervation of the amygdala: Dual-input synaptic plasticity and auditory fear conditioning

The neurobiology of Pavlovian fear conditioning is investigated at the synaptic, cellular, systems, and behavioral level. Sensory information for such learning is relayed to the lateral amygdala (LA) through dual cortical/subcortical afferents---each projection transmitting auditory information of varying complexity. Subjected to repeated pairings of an innocuous CS and aversive US, CS-CR neural associations develop that enable the expression of defensive behavior. Long-term potentiation (LTP) is the leading neurophysiological mechanism thought responsible for the formation and maintenance of the CS-CR connection(s). LTP and other experience-dependent forms of synaptic modification are discussed in Chapter 2, concentrating, in the final section, on LTP in the amygdala. Chapter 3 contains two studies investigating the LA postsynaptic receptor sites responsible for the acquisition and expression of conditional fear. The issue of time is investigated in Chapter 4. Specifically, the ability of fear conditioned rats to temporally encode the conditioning interstimulus interval (ISI) is explored---based on the predictions of a computational model developed by our laboratory. Finally, Chapter 5 details a perceptually complex acoustic cue that must be relayed to LA through its cortical afferents---offering the possibility that the two auditory inputs to LA can be functionally dissociated.