Sex and handedness effects on corpus callosum morphology in chimpanzees (Pan troglodytes)

Abstract

Findings suggest that in humans, sex and hand preference may be associated with the size of the corpus callosum (CC). The authors measured CC morphology from MRIs in 67 chimpanzees (Pan troglodytes) to see whether similar effects were present in this species. Hand preference was assessed by performance on 4 tasks, and chimpanzees were classified as left-handed, right-handed, or ambidextrous. In a subsequent analysis, the chimpanzees were reclassified into 2 groups: right-handed and left-handed. The results revealed no sex difference in CC area, but significant effects of hand preference were found for several CC regions (rostrum body, anterior midbody, posterior midbody, isthmus, and splenium) and for overall CC size, with left-handed chimpanzees exhibiting significantly smaller CC measurements than right-handed chimpanzees. The results indicate that lateralized hand use in chimpanzees, as in humans, is associated with variation in CC size.

Figure 1

Midsagittal view of the chimpanzee corpus callosum. The seven subdivisions used for measurement are depicted here as numbers 1–7: 1 = rostrum, 2 = genu, 3 = rostrum body, 4 = anterior midbody, 5 = posterior midbody, 6 = isthmus, and 7 = splenium.

Figure 2

Mean(± SE) residual total corpus callosum (CC) values as a function of handedness.