Morphometry of the adult human corpus callosum: lack of sexual dimorphism.

A major sexual dimorphism in the mid-sagittal cross-section of the adult human corpus callosum was described by de Lacoste-Utamsing & Holloway (1986), the splenium in female brains being larger and more bulbous than in the brains of males. The implications of such a large difference for neurobiology are considerable. The initial series reported was small, comprising five female and nine male brains, although some of the differences recorded achieved statistical significance at the 0 1 % level. Subsequently the same authors extended their observations to 38 fetal and a further 16 adult brains and found sexual dimorphism during development and in adulthood (de Lacoste, Holloway & Woodward, 1986; Holloway & de Lacoste, 1986). Yoshi et al. (1986) also found that the splenium was more bulbous in females. Their study included 19 female and 14 male brains. Sexual dimorphism of the splenium has also been described in 15 pongid brains but not in other non-human primate species (de Lacoste & Woodward, 1988). However, Bell & Variend (1985), who examined 44 brains, (28 male, 16 female) from children ranging in age from term infants to 14 years found no evidence of sexual dimorphism in the corpus callosum. Witelson (1985), in a study of the corpus callosum with respect to handedness, noted in passing that she was unable to detect any sexual dimorphism in the corpus callosum in a sample of 42 adult subjects. Studies by Weber & Weis (1986), Byne, Bleier & Houston (1988) and Demeter, Ringo & Doty (1988) also failed to find a difference between the sexes. These three groups of workers examined a total of 108 brains. In view of the uncertainty concerning the existence of a major anatomical difference between the brains of men and women, we have studied 33 adult human brains, 17 male and 16 female, using a -variety of morphometric approaches to see whether we could detect such a difference.