Interhemispheric differences in gene expression of the cerebral cortex in humans and macaque monkeys

Handedness and language are two well-studied examples of asymmetrical brain function in humans. Approximately 90% of humans exhibit a right-hand preference, and the vast majority shows left-hemisphere dominance for language function. Although genetic models of human handedness and language have been proposed, the actual gene expression differences between cerebral hemispheres in humans remain to be fully defined. In the present study, gene expression profiles were examined in both hemispheres of three cortical regions involved in handedness and language in humans and their homologues in rhesus macaques: ventrolateral prefrontal cortex, posterior superior temporal cortex (STC), and primary motor cortex. Although the overall pattern of gene expression was very similar between hemispheres in both humans and macaques, weighted gene correlation network analysis revealed gene co-expression modules associated with hemisphere, which are different among the three cortical regions examined. Notably, a receptor-enriched gene module in STC was particularly associated with hemisphere and showed different expression levels between hemispheres only in humans. Rhesus macaque (Macaca mulatta) brains were dissected from frozen samples collected post-mortem from 5 different individuals. From each hemisphere, samples were dissected from the inferior ramus of the arcuate sulcus in the ventrolateral prefrontal cortex (which is homologues to area 44 of human Broca's area), the posterior superior temporal cortex (homologue of Wernicke's area), and the primary motor cortex from the forelimb control region. The macaque brains were obtained from Wisconsin National Primate Research Center (Madison, WI). All animals were housed in accordance with NIH, USDA, and AWA regulations, and overseen by the IACUCs of the respective institutions (National Research Council (US) Committee for the Update of the Guide for the Care and Use of Laboratory Animals, 2011). The time between death and tissue freezing was, in those cases for which this information was available, never longer than 6 h. ---------------------------- This represents the Rhesus data only