Sex differences in human brain asymmetry: a critical survey

TLDR

Brain asymmetry is characterized by left‑hemisphere language dominance and right‑hemisphere nonverbal processing, and studies over the past two decades have reported scattered sex differences in the degree of this specialization. This review critically examines whether significant sex differences exist in verbal or spatial cerebral lateralization and whether one sex exhibits a more symmetrical brain organization. The authors analyze right‑handed adult data from clinical lesion studies, dichotic listening, tachistoscopic, sensorimotor, anatomical, electrophysiological, and developmental research, noting that most evidence is retrospective and descriptive. The evidence indicates that the male brain is generally more asymmetrically organized than the female brain for both verbal and nonverbal functions, a pattern that emerges mainly in mature adults and is rarely observed in childhood.

Abstract

Abstract Dual functional brain asymmetry refers to the notion that in most individuals the left cerebral hemisphere is specialized for language functions, whereas the right cerebral hemisphere is more important than the left for the perception, construction, and recall of stimuli that are difficult to verbalize. In the last twenty years there have been scattered reports of sex differences in degree of hemispheric specialization. This review provides a critical framework within which two related topics are discussed: Do meaningful sex differences in verbal or spatial cerebral lateralization exist? and, if so, Is the brain of one sex more symmetrically organized than the other? Data gathered on right-handed adults are examined from clinical studies of patients with unilateral brain lesions; from dichotic listening, tachistoscopic, and sensorimotor studies of functional asymmetries in non-brain-damaged subjects; from anatomical and electrophysiological investigations, as well as from the developmental literature. Retrospective and descriptive findings predominate over prospective and experimental methodologies. Nevertheless, there is an impressive accummulation of evidence suggesting that the male brain may be more asymmetrically organized than the female brain, both for verbal and nonverbal functions. These trends are rarely found in childhood but are often significant in the mature organism.