Sexual dimorphism of the human corpus callosum from three independent samples: Relative size of the corpus callosum

Abstract

Three independent autopsy samples of brains without apparent neuropathology were studied to ascertain whether there was sexual dimorphism in the human corpus callosum (CC). Using planimetric measurements on midsagittal brain sections, several morphometric features of the CC were studied: total callosal area, maximum dorsoventral splenial width, the posterior one fifth of the total area of the CC (mostly splenium), and brain weight. Ratio data correcting for brain size were also studied. In all samples, absolute brain size was larger in males, and significantly so. Measurements of splenial dorsoventral width were higher in females than males, but not significantly, except in the Australian sample. Total callosal area was absolutely higher in the Australian female sample than in males, and almost equal in the two American samples, without statistically significant differences. The posterior one-fifth area (splenium) was larger for females in each of the samples. The variables which were corrected for brain size were usually significantly larger in females, although this pattern varied in each sample. The statistical pattern of sexual dimorphism for the human CC differs from that found in most other neural structures, such as the amygdaloid nucleus, cerebellum, hippocampus, and thalamus. The absolute sizes of these structures are always significantly larger in males. When corrected for brain size, the relative sizes are not significantly larger. The CC is the only structure to show a larger set of relative measures in females.

Sex Differences in the Human Corpus Callosum: Myth or Reality?

“…Articles by Witelson (126) and Clarke et al (25) contain summary tables and brief reviews of studies of sex differences in the corpus callosum, although no attempt is made to integrate the results statistically, and few studies are examined (less than 15). Holloway et al (66) include an appendix in which 15 studies are described and their similarity to Holloway et al' s is commented upon. Byne (21) and Fausto-Sterling (46) review 18 and 17 recent studies, respectively, and reach conclusions similar to ours, which are based on more studies and a formal metaanalysis.…”

“…Ten of these (A5, A14, A19, A29, A33, A35, A38, A43, A48, A49; (92,106,56,104,45,2,66,131,101,105)) found no sex difference in the ratio, whereas eight found females to have a significantly higher ratio (A4, A8, A15, A24, A25, A27, A37, A39; (67,76,117,31,44,65,66)). In some instances, a sex difference that was apparent with a ratio measure was not significant when analysis of covariance was used with the same data (e.g.…”

“…Clarke et al (25) and Prokop et al (102) were each treated as two separate studies because two different methods were used to examine two different groups of subjects in each study. Holloway et al (66) was treated as three separate studies because three different samples of subjects were examined.…”

“…Although none employed the multiple regression method that we propose for the data of Bean and Mall, seven used analysis of covariance in almost the same way, and six found no sex differences in CC size when brain or cortex size was used as a covariate (A2, A23, A37/38/39, A42, A44, A46; (9,126,66,130,18,63)). Only Holloway et al (A27; (65)) found any significant sex difference when cortical area was used as a covariate (female > male; p = 0.018).…”

Sexual attractiveness: a comparative approach of morphological, behavioral neurophysiological signaling in women and nonhuman primate females

“…Replacement of ovauian houmones into the dousal uaphe nuclei uegion of macaque buains alteued the mRNA expuession uates of components involved in seuotonin metabolism (Pecins-Thompson et al, 1998). The uhombencephalic uaphe nuclei complex is the ouigin of the seuotoneugic system wheue seuotoneugic fibeus puoject into almost all buain aueas (Holloway, 1993). Loweu amounts of buain seuotonin concentuations aue uelated, fou example, to depuession, anxiety, and impaiued cognition (Wallneu & Machatschke, 2009).…”