Sex, handedness, and the morphometry of cerebral asymmetries on magnetic resonance imaging.

Cerebral morphometry of linear measurements and hemispheric, frontal, temporal and parietal areas on MRI of 104 normal adults was analyzed for sex and handedness and right-left differences. The right hemisphere was significantly larger across all groups, but the left frontal width and area was larger in left handers. MANOVA showed separate effects of hand and sex for linear measures; right-handers had larger right anterior frontal, and left parietal and occipital widths. Ratios of L - R/L + R eliminated sex differences related to overall brain size, however, a significant sex-by-hand interaction was shown by the parietal area ratios, indicating larger left side in right-handed males and left-handed females. A 3-dimensional 'torque' was postulated, where the upper and rostral portions of the hemispheres were larger on the right and the lower and caudal parts equal, or slightly larger on the left. The relationship of anatomical asymmetries, sex and handedness is multi-dimensional, and may explain some of the variability of normal cognitive functions and deficits after brain damage.