Your two amygdalae keep separate memories and may handle emotions differently
Deep in each temporal lobe sits an almond-shaped cluster of thirteen nuclei that tags experiences with fear, pleasure and meaning. Electrically stimulating the right one tends to trigger fear or sadness, while the left can call up happiness too. And the two sides mature on different schedules.
Karl Friedrich Burdach identified and named the amygdala in 1822. It is a paired structure, one in each hemisphere, counted as part of the limbic system and made up of many nuclei with their own subdivisions. The main groups are the basolateral complex, which talks to the prefrontal cortex and hippocampus; the central nucleus, which sends dense projections to the brainstem; and the cortical and medial nuclei, linked to smell and the hypothalamus. In primates it holds about 32 kinds of neuron.
Its best-studied job is fear learning. Sensory signals arrive in the lateral part of the basolateral complex, where they get linked to whatever unpleasant event they predict, probably through long-term potentiation, a lasting strengthening of connections between neurons. The central nucleus then drives the response: freezing or fleeing, a racing heart, a surge of stress hormones. Damage to the amygdalae disrupts both learning and expressing this kind of Pavlovian fear. One patient whose amygdalae had degenerated on both sides remembered less of a violent illustrated story than people with healthy ones.
It is not only about threat. The amygdala also supports reward learning, with distinct neurons answering good and bad stimuli, and lesions of the central nucleus reduce appetitive learning in rats. The two sides differ too. The right is tied to negative emotion and to linking places and times with feelings, while evidence suggests the left contributes to the reward system.
Sex differences are subtler than raw numbers suggest. Male amygdalae are on average 10.6 percent bigger, but that gap vanishes once overall brain size is accounted for. Functional patterns differ, though. In brain scans after an emotional film, stronger recall tracked the left amygdala in women and the right in men, and patients with one-sided damage showed a matching split in impaired decision-making. The left amygdala also peaks about 1.5 to 2 years earlier in development than the right.
Source: Amygdala
