Vertex- and atlas-based comparisons in measures of cortical thickness, gyrification and white matter volume between humans and chimpanzees

What changes in cortical organisation characterise global and localised variation between humans and chimpanzees remains a topic of considerable interest in evolutionary neuroscience. Here, we examined regional variation in cortical thickness, gyrification and white matter in samples of human and chimpanzee brains. Both species were MRI scanned on the same platform using identical procedures. The images were processed and segmented by FSL and FreeSurfer and the relative changes in cortical thickness, gyrification and white matter across the entire cortex were compared between species. In general, relative to chimpanzees, humans had significantly greater gyrification and significantly thinner cortex, particularly in the frontal lobe. Human brains also had disproportionately higher white matter volumes in the frontal lobe, particularly in prefrontal regions. Collectively, the findings suggest that after the split from the common ancestor, white matter expansion and subsequently increasing gyrification occurred in the frontal lobe possibly due to increased selection for human cognitive and motor specialisations.