Cerebral Hemispheric Asymmetry in Humans

TLDR

Morphological asymmetry of the frontal operculum and temporal planum can be detected from the 29th week of gestation. Later development shows the left planum is generally larger, while the right planum varies from absent to larger, with a higher proportion of females in the latter group, suggesting that a higher percentage of individuals may have right‑sided or bilateral speech dominance, that early morphological asymmetry influences speech representation after insults, and that clinical data should be examined for sex‑specific hemispheric organization.

Abstract

Morphological asymmetry of the frontal operculum and temporal planum becomes measurable at the 29th week of gestation. There is evidence of subsequent differential development of the planum in favor of the left, with the left planum larger than the right. While both the frontal operculum and left planum were always present, the right planum ranged in size from absent (10%) to larger than the left (about 10%). Females predominated (<i>P</i>&lt;.05) in the latter group. The findings suggest that (1) a higher percentage of persons may have right-sided cerebral speech dominance or bilateral cerebral representation for speech than has been assumed previously; (2) a predetermined morphological asymmetry contributes to establishing the ultimate pattern of cerebral speech representation following an early insult to a predisposed hemisphere; and (3) it is necessary to scrutinize clinical material for the differential organization of hemispheric development between sexes.