Handedness is associated with asymmetries in gyrification of the cerebral cortex of chimpanzees.

Gyrification of the cerebral cortex reflects complexity in cortical folding during development of the brain. In this paper, we evaluated whether chimpanzees show asymmetries in gyrification and if variation in gyrification asymmetries were associated with handedness. Magnetic resonance images were obtained in a sample of 76 chimpanzees, and gyrification measures were obtained from 10 equally spaced slices of the cortex. Asymmetry quotients (AQs) in gyrification were compared for 4 measures of handedness including reaching, coordinated bimanual actions, manual gestures, and throwing. Overall, the chimpanzees showed significant differences between the right and left hemispheres that were region specific. Significant differences in AQ's were found in right- and nonright-handed chimpanzees for throwing and, to a lesser degree, for manual gestures. Increasing age was associated with increasing gyrification in the prefrontal regions, particularly in female chimpanzees. The results indicate that variation in gyrification between hemispheres is associated with functional measures of laterality in chimpanzees.