The auditory conditioned stimulus (CS) and somatosensory (pain) unconditioned stimulus (US) converge in the lateral amygdala (LA). The LA receives inputs from each system via both thalamic and cortical inputs. CS-US convergence induces synaptic plasticity in LA such that after conditioning the CS flows through the LA to activate the central amygdala (CE) via intraamygdala connections. CE in turn controls the expression of behavioral (freezing), autonomic and endocrine responses that are components of the fear reaction. Other abbreviations: B, basal amygdala; CG, central gray; LH, lateral hypothalamus; ITC, intercalated cells of the amygdala; PVN, paraventricular nucleus of the hypothalamus.