The amygdala is a collection of nuclei in the medial temporal lobe that plays a central role in processing emotionally significant stimuli, particularly those related to threat and fear. It evaluates the emotional significance of sensory input, triggers fear responses, and modulates memory consolidation for emotional events. Through its connections with cortical, subcortical, and brainstem structures, the amygdala influences perception, attention, decision-making, and social behavior.
Functions
In fear conditioning, the amygdala (particularly the lateral and central nuclei) is the essential site where associations between neutral stimuli and aversive outcomes are formed and stored. The amygdala also modulates memory consolidation in the hippocampus, explaining why emotional events are better remembered than neutral ones (McGaugh's modulation hypothesis). In social cognition, the amygdala evaluates facial expressions of emotion, particularly fear, and processes social signals about trustworthiness and threat.
Patient S.M., with bilateral amygdala destruction due to Urbach-Wiethe disease, has been extensively studied by Ralph Adolphs and colleagues. She cannot recognize fear in facial expressions, does not experience fear in normally terrifying situations, shows no fear conditioning, and lacks the normal emotional enhancement of memory. Her case provides a natural lesion study demonstrating the amygdala's essential role in fear processing and emotional memory.