1. ¹Department of Neurology, University of Cologne, Köln, Germany
2. ²Max-Planck-Institute for Neurological Research, Cologne, Köln, Germany

Correspondence: Dr A Thiel, Department of Neurology, University of Cologne, Kerpenerstr. 62, Köln D-50937, Germany. E-mail: A.Thiel@pet.mpin-koeln.mpg.de

Received 31 January 2006; Revised 19 April 2006; Accepted 1 May 2006; Published online 7 June 2006.

Abstract

Neuroimaging studies in right-handed patients with left hemisphere brain lesions have demonstrated a shift of language activity from left to right inferior frontal gyrus (IFG). This shift may be caused by greater right hemisphere dominance before the injury or by reduced inhibitory activity of the injured left hemisphere. We simulated a brain lesion applying transcranial –magnetic stimulation over left IFG in normal subjects, while simultaneously measuring language activity with positron –emission tomography. Interference with transcranial –magnetic stimulation decreased activity in left and increased it in right IFG in all subjects. We thus demonstrate for the first time that a rightward shift of language activity is caused by the brain lesion and not by greater right-hemisphere dominance, thus supporting the hypothesis of reduced transcallosal inhibition.