Human and nonhuman primate brains: Are they allometrically scaled versions of the same design?


  • James K. Rilling

    1. Department of Anthropology, Department of Psychiatry and Behavioral Sciences, Yerkes Regional Primate Research Center, Emory University, Atlanta, GA 30322
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    • James K. Rilling is an Assistant Professor of Anthropology at Emory University, with a secondary appointment in the Department of Psychiatry and Behavioral Sciences. Dr. Rilling and his colleagues use non-invasive functional brain imaging techniques to compare brain structure and function in monkeys, apes and humans, with the goal of identifying human brain specializations and informing our knowledge of human brain evolution. His lab also investigates the neural bases of human social behavior by measuring brain function with fMRI as subjects play interactive games with human partners.


Allometric analyses of brain structure sizes across the primate order demonstrate that human, ape, and other anthropoid brains are not simply allometrically scaled versions of the same generalized design. Both human and ape brains exhibit specializations with respect to other anthropoid brains. Ape specializations include elaboration of the cerebellum (all apes) and frontal lobes (great apes only), and probably connectivity between them. Human brain specializations include an overall larger proportion of neocortex, with disproportionate enlargement of prefrontal and temporal association cortices; an apparent increase in cerebellar connections with cerebral cortical association areas involved in cognition; and a probable augmentation of intracortical connectivity in prefrontal cortex.