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

Background: Disorders of language classically occur after left brain lesions, and disorders of spatial attention after right brain lesions. It is unclear whether the hemispheric dissociation of functions is a fixed pattern of brain organization. Objective: The authors determined whether lateralization of language and lateralization of spatial attention also dissociate in people 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 random basis from a sample of 326 healthy volunteers examined with functional transcranial Doppler sonography, (fTCD) for language dominance. In these subjects, hemispheric lateralization of cerebral perfusion during a line bisection task was determined with fTCD. Results: The authors found a dissociation between dominance for language and spatial attention in all but four subjects. In the latter subjects, there was a significant lateralization to the right hemisphere for both tasks. The four subjects showed normal intellectual, linguistic, and spatial performance, with normal EEG and MRI scans of the brain. Conclusion: Even in the absence of brain pathology, the same hemisphere can be dominant in control of both language and spatial attention.