LANGUAGE-ASSOCIATED CORTICAL REGIONS ARE PROPORTIONALLY LARGER IN THEFEMALE BRAIN

Background: Many studies have demonstrated significant sexual dimorphi sm in verbal ability. However, few studies have examined anatomical di fferences between the sexes that may underlie such dimorphism. Objecti ve: To examine sex differences in the absolute and proportional volume s of the main language-associated regions of the cerebral cortex. Desi gn and Main Outcome Measures: Control neuropathological case series of consecutive autopsies from a teaching hospital. No significant age-re lated volume changes were identified in the sample. Two language-assoc iated cortical regions, the superior temporal gyrus (part of the Werni cke area) and its subdivisions (planum temporale, Heschl gyrus, and an terior superior temporal gyrus) and the inferior frontal gyrus (Broca area in the dominant hemisphere), and a non-language-associated region , the frontal pole, were measured using stereological techniques in br ains fixed with formaldehyde solution serially sectioned at 3-mm inter vals. Volume comparisons between the sexes and between brain hemispher es were performed using 2-way analysis of variance. Setting: Studies w ere conducted at the University of Sydney and the Prince of Wales Medi cal Research Institute, Sydney, Australia. Patients: Ten males and Il females free from neurologic or neuropathological abnormalities. Resul ts: The volume of the superior temporal cortex, expressed as a proport ion of total cerebral volume, was significantly larger in females comp ared with males (17.8% increase; P = .04). This was accounted for by 1 section of the superior temporal cortex, the planum temporale, which was 29.8% larger in females (P = .04). In addition, the cortical volum e fraction of the Broca area in females was 20.4% larger than in males (P = .05). In contrast, no significant differences were found in the proportional volume of the frontal pole or in regional volumes between the left and right hemispheres in either sex group. Conclusions: Our results suggest that females have proportionally larger Wernicke and B roca language-associated regions compared with males. These anatomical differences may correlate with superior language skills previously de monstrated in females.