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Soc Cogn Affect Neurosci. 2016 Mar;11(3):413-22. doi: 10.1093/scan/nsv128. Epub 2015 Oct 16.

Differential serotonergic innervation of the amygdala in bonobos and chimpanzees.

Author information

Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC 20052,
Department of Psychiatry and Behavioral Sciences, University of California, Davis, CA 95616.
Department of Ecology, Evolution and Organismal Biology, Kennesaw State University, Kennesaw, GA 30144.
Comparative Pathology Lab - RARC, University of Wisconsin, Madison, WI 53726.
Fishberg Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029.
Neuroscience Institute and Language Research Center, Georgia State University, Atlanta, GA 30302, and Department of Developmental and Cognitive Neuroscience, Yerkes National Primate Research Center, Atlanta, GA 30322.
Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC 20052.


Humans' closest living relatives are bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), yet these great ape species differ considerably from each other in terms of social behavior. Bonobos are more tolerant of conspecifics in competitive contexts and often use sexual behavior to mediate social interactions. Chimpanzees more frequently employ aggression during conflicts and actively patrol territories between communities. Regulation of emotional responses is facilitated by the amygdala, which also modulates social decision-making, memory and attention. Amygdala responsiveness is further regulated by the neurotransmitter serotonin. We hypothesized that the amygdala of bonobos and chimpanzees would differ in its neuroanatomical organization and serotonergic innervation. We measured volumes of regions and the length density of serotonin transporter-containing axons in the whole amygdala and its lateral, basal, accessory basal and central nuclei. Results showed that accessory basal nucleus volume was larger in chimpanzees than in bonobos. Of particular note, the amygdala of bonobos had more than twice the density of serotonergic axons than chimpanzees, with the most pronounced differences in the basal and central nuclei. These findings suggest that variation in serotonergic innervation of the amygdala may contribute to mediating the remarkable differences in social behavior exhibited by bonobos and chimpanzees.


amygdala; bonobo; brain evolution; chimpanzee; serotonin

[Available on 2017-03-01]
[Indexed for MEDLINE]
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