Motor and communicative correlates of the inferior frontal gyrus (Broca's area) in chimpanzees

The inferior frontal gyrus (IFG) encompasses Broca's area, a brain region implicated in a variety of cognitive and linguistic functions. For instance, clinical and experimental data suggest that the left IFG plays an important role in language and speech. In this paper, I briefly summarize data on the sulci and morphological landmarks that define the IFG in humans, chimpanzees and monkeys. I also present some preliminary data on the surface area, mean depth and gray matter thickness of the three primary sulci that comprise the IFG in the chimpanzee brain including the fronto-orbital, precentral inferior and inferior frontal sulci. I further present data on associations between individual variation in asymmetries of each sulcus with measures of oro-facial motor control and tool use skill. The implications of these findings for different theories on the evolution of language and higher order motor and cognitive functions in primates are discussed.