Brain lateralization in primates and its evolution in hominids

Abstract

Recent studies suggest that vocal communication and visuospatial processing are lateralized to left and right hemispheres respectively in monkeys of the genus Macaca, as they are in humans. The fundamental neurological substrate that forms the basis for complex cerebral asymmetries in Homo sapiens may therefore have been established remarkably early in anthropoid evolution. The tendency toward cortical lateralization has been greatly elaborated in human evolution, such that at least 90% of extant humans are right‐handed. Numerous data support an association of the left human hemisphere with time‐sequencing, language skills, certain neurochemical asymmetries, and specific psychiatric disorders. The right hemisphere, on the other hand, is associated with holistic processing, visuospatial and musical abilities, emotional processing, and its own neurochemical and psychiatric properties. Although a controversial topic, there appears to be slight but significant sexual dimorphism in certain skills associated with cortical lateralization in humans. Females excel at language and fine motor skills, as well as emotional decoding and expression; males are relatively adept at composing music and exhibit visuospatial and mathematical skills. Various scenarios that account for these differences are reviewed, and it is concluded that dimorphism in these behaviors may be due in part to hormonal priming involved in prenatal gender differentiation. Copyright © 1987 Wiley‐Liss, Inc., A Wiley Company