Neurobiology of fear responses: the role of the amygdala.

Evidence from many different laboratories using a variety of experimental techniques and animal species indicates that the amygdala plays a crucial role in conditioned fear and anxiety, as well as attention. Many amygdaloid projection areas are critically involved in specific signs used to measure fear and anxiety. Electrical stimulation of the amygdala elicits a pattern of behaviors that mimic natural or conditioned fear. Lesions of the amygdala block innate or conditioned fear, as well as various measures of attention, and local infusions of drugs into the amygdala have anxiolytic effects in several behavioral tests. N-methyl-D-aspartate (NMDA) receptors in the amygdala may be important in the acquisition of conditioned fear, whereas non-NMDA receptors are important for the expression of conditioned fear. The peptide corticotropin-releasing hormone appears to be especially important in fear or anxiety and may act within the amygdala to orchestrate parts of the fear reaction.