Process versus product in social learning: comparative diffusion tensor imaging of neural systems for action executionobservation matching in macaques, chimpanzees, and humans. Cereb. Cortex. doi: 10.1093/cercor/bhs097. [Epub ahead of print

Social learning varies among primate species. Macaques only copy the product of observed actions, or emulate, while humans and chim-panzees also copy the process, or imitate. In humans, imitation is linked to the mirror system. Here we compare mirror system connec-tivity across these species using diffusion tensor imaging. In maca-ques and chimpanzees, the preponderance of this circuitry consists of frontal–temporal connections via the extreme/external capsules. In contrast, humans have more substantial temporal–parietal and frontal–parietal connections via the middle/inferior longitudinal fasci-culi and the third branch of the superior longitudinal fasciculus. In chimpanzees and humans, but not in macaques, this circuitry in-cludes connections with inferior temporal cortex. In humans alone, connections with superior parietal cortex were also detected. We suggest a model linking species differences in mirror system connec-tivity and responsivity with species differences in behavior, including adaptations for imitation and social learning of tool use