The primate neocortex in comparative perspective using magnetic resonance imaging

In this study we use neuroanatomic data from living anthropoid primate subj ects to test the following three hypotheses: (1) that the human neocortex i s significantly larger than expected for a primate of our brain size, (2) t hat the human prefrontal cortex is significantly more convoluted than expec ted for our brain size, and (3) that increases in cerebral white matter vol ume outpace increases in neocortical gray matter volume among anthropoid pr imates. Whole brain MRI scans were obtained from 44 living primate subjects from II different species. Image analysis software was used to calculate t otal brain volume, neocortical gray matter volume, cerebral white matter vo lume, and the cross sectional area of the spinal cord in each scan. Allomet ric regression analyses were used to compare the relative size of these bra in structures across species, with an emphasis on determining whether human brain proportions correspond with predictions based on nonhuman primate al lometric trajectories. All three hypotheses were supported by our analysis. The results of this study provide additional insights into human brain evo lution beyond the important observation that brain Volume approximately tri pled in the hominid lineage by demonstrating that the neocortex was uniquel y modified throughout hominid evolution. These modifications may constitute part of the neurobiological substrate that supports some of our species mo st distinctive cognitive abilities. (C) 1999 Academic Press.