Language lateralization in healthy right-handers

TLDR

Studies of language lateralization have largely relied on brain‑lesion patients, leaving the prevalence of atypical right‑hemisphere dominance in healthy right‑handers poorly understood. The authors aimed to test the assumption that atypical language dominance is exceedingly rare by measuring lateralization in 188 strongly right‑handed adults. Using a validated, non‑invasive perfusion‑based technique during a word‑generation task, they quantified hemispheric perfusion differences in the middle cerebral artery territories. They found a bimodal distribution of lateralization, equal prevalence in men and women, and 7.5 % right‑hemisphere dominance, indicating atypical dominance is considerably more common than previously thought.

Abstract

Our knowledge about the variability of cerebral language lateralization is derived from studies of patients with brain lesions and thus possible secondary reorganization of cerebral functions. In healthy right-handed subjects 'atypical', i.e. right hemisphere language dominance, has generally been assumed to be exceedingly rare. To test this assumption we measured language lateralization in 188 healthy subjects with moderate and strong right-handedness (59% females) by a new non-invasive, quantitative technique previously validated by direct comparison with the intracarotid amobarbital procedure. During a word generation task the averaged hemispheric perfusion differences within the territories of the middle cerebral arteries were determined. (i) The natural distribution of language lateralization was found to occur along a bimodal continuum. (ii) Lateralization was equivalent in men and women. (iii) Right hemisphere dominance was found in 7.5% of subjects. These findings indicate that atypical language dominance in healthy right-handed subjects of either sex is considerably more common than previously suspected.