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: righthanded 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. Keywords Pan troglodytes; corpus callosum; handednessThe corpus callosum (CC) is the major set of fibers connecting homologous and heterologous cortical regions in the left and right cerebral hemispheres as well as some subcortical structures of the brain (Bermudez & Zatorre, 2001;Gazzaniga, 2000). Its presence allows for interhemispheric communication of sensory and motor functions within the brain. Previous research has shown that projections through the CC proceed on an anterior-to-posterior gradient that roughly connects cortical regions from the frontal to occipital lobe (Witelson, 1989). The morphology of the CC has been the topic of considerable debate, particularly as it relates to sex differences and lateralization (Byne, Bleier, & Houston, 1988;Denenberg, Kertesz, & Cowell, 1991;Driesen & Raz, 1995;Habib et al., 1991;Jancke & Steinmetz, 1998;Peters et al., 2002;Westerhausen et al., 2003).The presence of a sexual dimorphism in the human CC was first reported by de LacosteUtamsing and Holloway (1982). In their study, de Lacoste-Utamsing and Holloway found that women had a larger and more bulbous splenium (posterior fifth of the CC) than did men. Furthermore, de Lacoste-Utamsing and Holloway found that when brain weight was accounted for, women had a larger overall CC. Significant findings of a dimorphism favoring a larger total CC area or regional CC area in female humans have been reported in subsequent studies on cadaver specimens as well as from in vivo imaging studies (Achiron, Lipitz, & Achiron, 2001;Bermudez & Zatorre, 2001;Burke & Yeo, 1994 Innocenti, 1989;Witelson, 1989); however, several studies have found no evidence of sex differences in the size of the CC (Bishop & Wahlsten, 1997;Driesen & Raz, 1995;Habib et al., 1991;Horton, Crawford, Harrington, & Downs, 2004;Witelson, 1985).In addition to sex differences in CC morphology, the relationship between handedness and CC morphology has also been considered. In one of the earliest studies, Witelson (1985) found that mixed-handed individuals (those who did not consistently use their right hand for specifi...

Effects of early adverse experiences on behavioural lateralisation in rhesus monkeys (Macaca mulatta)

“…Although no effort was made to systematically control for the rearing practices of each facility, each provides nursery-housed animals with environmental enrichment, conspecific age-mate social contact, and introduction into larger social groups following infancy. It is notable that differences in lateralisation in cerebral organisation, as reflected in the relative size of the corpus callosum to brain size or from direct measures of brain asymmetry, has also been reported in differentially reared rhesus (Sanchez, Hearn, Do, Rilling, & Herndon, 1998) and squirrel monkeys (Lyons, Afarian, Schatzberg, Saywer-Glover, & Moseley, 2002) but not in chimpanzees (Dunham & Hopkins, 2006;Hopkins, Dunham, Cantalupo, & Taglialatela, 2007). Thus, the differences in lateralisation seen between mother-and nursery-reared monkeys compared to chimpanzees appear to generalise to behavioural and brain measures.…”

Corpus Callosum Morphology in Capuchin Monkeys Is Influenced by Sex and Handedness

“…These conflicting results are due in part to the limitations of previous methodologies and unstandardized reporting of corpus callosum measures–some adjust for brain size while others do not. Similar sex differences in CC morphology have not been reported in any nonhuman primate species examined to date, including chimpanzees, Old World and New World monkeys [11]–[14], leading some to conclude that these sex differences reflect a unique adaptation in humans [15].…”

Performance asymmetries in tool use are associated with corpus callosum integrity in chimpanzees (Pan troglodytes): A diffusion tensor imaging study.

“…Differences in measurement of callosal size, sample size, and whether (or not) the callosal area is adjusted for brain size all likely contribute to the inconsistency of results. In the present study we adjusted the CC area for total brain volume in accordance with Smith (2005), as did Dunham and Hopkins (2006) and Hopkins et al (2007). However, in the present study the partitioning of the CC was based on DTI tractography (Phillips & Hopkins, 2012), whereas the previous studies employed a geometrically based method (Witelson, 1989).…”