A hypothetical fear conditioning circuit. Abbreviations: CN, cochlear nucleus; DH, dorsal horn of spinal cord; IC, inferior colliculus; LGN, lateral geniculate nucleus; MGN, medial geniculate nucleus; HIP, hippocampus; CTX, association cortex; POC, primary olfactory cortex; TE, auditory cortex; VC, visual cortex. Both auditory and visual stimuli send projections to ipsi- and contra-lateral side. Relatively predominant projections are denoted by thicker lines in the figure. Auditory pathways are divided into thalamo- and cortico-amygdalo pathways. The visual pathways to the amygdala are less well defined but also represented as combined thalamic and cortical inputs. The rest of the sensory inputs, such as olfactory, vestibular and gustatory, form important parts of complex stimuli, and it is represented as contextual stimulus pathways that centers around HIP and CTX, which receive inputs from various sensory cortical areas. The essential US pathways to the amygdala is currently unknown. From Kim JJ and Choi J-S (2002). Amygdalar circuits and synaptic mechanisms involved in Pavlovian fear conditioning. SaiboKougaku (Cell Technology) 21: 1022-1029.