Sex differences in hemispheric specialization: Hypothesis for the excess of dyslexia in boys

Abstract

Sex differences exist in the prevalence of dyslexia as well as in overall verbal ability. These sex differences may reflect sex differences in hemispheric specialization: males show strong left hemisphere specialization for verbal processing and strong right hemisphere specialization for spatial processing whereas females show greater bihemispheric participation in both verbal and spatial processing. The greater hemispheric specialization observed in males may have implications including: (1) lower verbal ability than in females, (2) higher spatial ability than in females, (3) reduced potential for shifting language to the right hemisphere after early life left hemisphere injury, and (4) diminished capacity to compensate for unfavorable left-right anatomic asymmetries of the posterior language zone. Lower overall verbal ability as well as an inability to spare certain language skills effectively in the face of either unfavorable cerebral asymmetries or early life left hemisphere insults may partially explain the excess of developmental language disorders (and dyslexia in particular) in boys.