A comparative study of corpus callosum size and signal intensity in capuchin monkeys (Cebus apella) and chimpanzees (Pan troglodytes).

The evolution of corpus callosum (CC) was integral to the development of higher cognitive processes and hemispheric specialization. An examination of CC morphology and organization across different primate species will further our understanding of the evolution of these specified functions. Using magnetic resonance imaging (MRI) as a non-invasive technique to measure CC size and to approximate the degree of myelination in the corpus callosum, we report differences in CC morphology and organization in capuchin monkeys and chimpanzees, two divergent primate species that have independently evolved several behavioral and anatomical characteristics. Species differences in CC morphology were detected, with chimpanzees having a larger overall CC compared to capuchin monkeys. Additionally, chimpanzees had the genu as the largest subdivision; in capuchin monkeys, the genu and splenium were the largest subdivisions. Sex differences in signal intensity were detected; capuchin monkey males had higher signal intensity values whereas chimpanzee females had higher signal intensity values. Thus, while capuchin monkeys and chimpanzees show some similarity in patterns of CC morphology, these species differ significantly in the regional organization of the CC.