Serotonergic innervation of the human amygdala and evolutionary implications

Objectives The serotonergic system is involved in the regulation of socio‐emotional behavior and heavily innervates the amygdala, a key structure of social brain circuitry. We quantified serotonergic axon density of the four major nuclei of the amygdala in humans, and examined our results in light of previously published data sets in chimpanzees and bonobos. Materials and methods Formalin‐fixed postmortem tissue sections of the amygdala from six...