Connectional asymmetry of the inferior parietal lobule shapes hemispheric specialization in humans, chimpanzees, and rhesus macaques

The inferior parietal lobule (IPL) is one of the most expanded cortical
regions in humans relative to other primates. It is also among the most
structurally and functionally asymmetric regions in the human cerebral
cortex. Whether the structural and connectional asymmetries of IPL
subdivisions differ across primate species and how this relates to
functional asymmetries remain unclear. We identified IPL subregions that
exhibited positive allometric in both hemispheres, scaling across rhesus
macaque monkeys, chimpanzees, and humans. The patterns of IPL subregions
asymmetry were similar in chimpanzees and humans, but no IPL asymmetries
were evident in macaques. Among the comparative sample of primates, humans
showed the most widespread asymmetric connections in the frontal,
parietal, and temporal cortices, constituting leftward asymmetric networks
that may provide an anatomical basis for language and tool use. Unique
human asymmetric connectivity between the IPL and primary motor cortex
might be related to handedness. These findings suggest that structural and
connectional asymmetries may underlie hemispheric specialization of the
human brain.