Lesion-induced right-hemispheric language and organization of nonverbal functions.

Early left-hemispheric brain lesions may lead to a reorganization of language into the right hemisphere. Language functions are consecutively spared, but visuospatial functions show slight deficits. Cortical 'crowding' of the right hemisphere has been suggested as an explanation for this effect, but no direct evidence has as yet been put forward. We examined six patients with early left-hemispheric brain lesions and subsequent right-hemispheric language organization with functional magnetic resonance imaging and compared their activation patterns in a verbal and two nonverbal tasks with the patterns of six controls. In the patient group, nonverbal functions were reorganized neither interhemispherically nor intrahemispherically. Instead, verbal and nonverbal functions were mediated by a common right-hemispheric network. This argues in favour of the 'crowding hypothesis'.