Cerebellar activation in right-hemispheric language dominance following early left-sided brain lesions

Introduction: The developing brain can compensate early left-hemispheric le-sions by reorganization of language function to the right hemisphere. Recent research has highlighted cerebellar involvement not only in sensorimotor con-trol but also in cognitive and language functions. Especially language pro-duction and verbal working memory tasks apparently depend on the right cerebellar hemisphere. In adults, recovery from stroke-induced aphasia can be associated with a shift of language activation from the left to the right cerebral, and from the right to the left cerebellar hemisphere. Methods: We analyzed fMRI data of a language production task for five adult patients with pre- or perinatally acquired lesions of the left cerebral hemisphere and sub-sequent right-hemispheric language reorganization, and compared it with data of healthy controls. Results: In both groups, activation was found in the posterio-lateral area of the cerebellar hemisphere. Similar to their mirror-reverse cerebral language organization pattern, patients showed left- instead of right-hemispheric cerebellar activation. Lateralization of cerebral and cerebellar activity correlated strongly in both groups. Discussion: In early left-hemispheric brain lesions, the representation of language areas is shifted in the hemispheres of cerebral cortex as well as in lateral cerebellum. In analogy to the recruitment of right-hemispheric homologues to classical language ar-eas, in these patients the cerebellar activation mirrored that of the controls as well. Taken into account that none of the patients suffered an infratentorial lesion, these findings emphasize that the reorganization process initiated by an early unilateral brain lesion is not restricted to the cortical network but in-volves also the cerebellum.