Language and spatial attention can lateralize to the same hemisphere in healthy humans

Background: Disorders of language classically occur after left brain lesion s, and disorders of spatial attention after right brain lesions. It is uncl ear whether the hemispheric dissociation of functions is a fixed pattern of brain organization. Objective: The authors determined whether lateralizati on of language and lateralization of spatial attention also dissociate in p eople with atypical (i.e., right hemispheric) language dominance. Methods: The authors selected 10 subjects with typical, i.e., left hemispheric, and 10 with atypical, i.e., right hemispheric, language representation on a ran dom basis from a sample of 326 healthy volunteers examined with functional transcranial Doppler sonography, (fTCD) for language dominance. In these su bjects, hemispheric lateralization of cerebral perfusion during a line bise ction task was determined with fTCD. Results: The authors found a dissociat ion between dominance for language and spatial attention in all but four su bjects. In the latter subjects, there was a significant lateralization to t he right hemisphere for both tasks. The four subjects showed normal intelle ctual, linguistic, and spatial performance, with normal EEG and MRI scans o f the brain. Conclusion: Even in the absence of brain pathology, the same h emisphere can be dominant in control of both language and spatial attention .