The evolution of the prefrontal brain areas in primates: a volumetric study

The evolution of the dorsolateral and orbitofrontal components of the prefrontal region of the primate brain presents an interesting picture of the evolution of the executive functions in these species. Considering that different selection pressures might lead to volumetric changes in certain areas of the primate brain, an attempt was made to elucidate the different relative expansion patterns of sub-regions of the prefrontal area related to different classes of executive functioning – emotional/motivational and meta-cognitive. Analysis conducted on volumetric data collected from 20 primate brains representing 17 different species, confirmed that the dorsolateral section increases in line with the expansion of the whole telencephalon relative to the body mass, while the prefrontal area, with more pronounced effect of the orbitofrontal sector, increases in line with the expansion of white matter relative to neocortex even after correction for phylogenetic dependence. The findings are analysed through the scope of the evolution of the executive functions and even though showing that the PF region is expanding with the increase in white matter, suggest that increased volume of DL and OF sub-regions is not necessary requirement for complex executive functioning and such expansions might have occurred in different primate families at different evolutionary time points.