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. Author manuscript; available in PMC: 2014 Jul 1.
Published in final edited form as: Horm Behav. 2013 Jul;64(2):380–389. doi: 10.1016/j.yhbeh.2013.01.016

Figure 1. Neural circuitry of fear expression and extinction.

Figure 1

(A) During acquisition and expression of conditioned fear, projections from PL and thalamic nuclei (mediating converging sensory information) excite LA neurons, while hippocampal projections (mediating contextual inputs) lead to excitation of BA neurons directly or indirectly via connections with PL. LA and BA neurons activate CE output neurons, which project to downstream brainstem and hypothalamic nuclei responsible for mediating physiological responses, resulting in fear expression. (B) During extinction of conditioned fear, hippocampal projections (mediating contextual inputs) lead to divergent excitation of IL neurons and inhibition of BA neurons. IL projections directly activate GABAergic ITC cells within the amygdala. Integration of ITC, BA, and LA inputs during extinction results in a suppression of CE output neurons, resulting in a lack of physiological response and suppression of fear expression. Arrowheads delineate pathway excitation; straight ends delineate pathway inhibition. (BA, basal amygdala; LA, lateral amygdala; CE, central amygdala; vmPFC, ventromedial prefrontal cortex; PL, prelimbic cortex; IL, infralimbic cortex; ITC, intercalated cells). *For simplicity, connection arrows are delineated as being unidirectional, although bidirectional projections exist.