Microcircuits of the Amygdala

This chapter reviews the unique microcircuits within the subdivisions of the amygdala. Microcircuits of the amygdala remain somewhat of an enigma. The amygdala itself is comprised of laterally located glutamatergic projection neuron structures, which are cortical-like, and medially located GABA projection neuron structures, which resemble neurons of the striatum. Within these are many nuclei and subnuclei that are distinguished on histologic, hodologic, and functional criteria. Significant progress has been made in understanding the organization of microcircuits in the lateral amygdala (LA) and central amygdala (CE), which play important roles in fear learning and fear memory, and the intercalated neurons (ITC), which regulate fear extinction. Emerging data indicate a structured excitatory microcircuit within the LA. Local axon collaterals of excitatory projection neurons are regulated by transverse modules of local GABA inhibition, which control excitation in the dorsal to ventral and ventral to dorsal planes. Bidirectional excitation in this plane may form recurrent networks that contribute to the temporal coordination of sensory signals integrated into the Lad network. Future work on amygdala microcircuits will continue to yield important data on how microcircuits regulate learning, memory, and behavior.