Finally, we will consider how evidence from studies that

employ TMS and tDCS contributes to the understanding of language recovery mechanisms. There is considerable evidence that perilesional areas of the left hemisphere acquire or reacquire language ability in the weeks and months following injury. It has long been accepted that the buy 17-AAG size of left hemisphere infarction in perisylvian language areas correlates with initial aphasia severity and inversely with aphasia recovery (Kertesz, Harlock, & Coates, 1979). A number of functional imaging studies of nonfluent aphasic patients have also demonstrated that better spontaneous language recovery is associated with greater activation of left-hemisphere structures (Karbe Z-VAD-FMK purchase et al., 1998, Karbe et al., 1998, Miura et al., 1999 and Warburton et al., 1999). Left hemisphere activation has been associated with better language improvement among nonfluent aphasic patients who undergo speech therapy (Cornelissen et al., 2003). In patients with fluent aphasia it has

been observed that efficient restoration of language is more frequently achieved if left temporal language networks are relatively well-preserved (Gainotti, 1993). While the mechanisms underlying increased perilesional activation in language recovery have not been fully elucidated, one important contributor may be the release of inhibitory input from the lesioned cortex, leading to increased activity in nearby cortical areas. Evidence indicates that unilateral injury—such as left-hemisphere lesions that give rise to aphasia—can lead to cortical disinhibition in at least two regions: (1) neighboring ipsilesional cortical areas and (2) contralesional homotopic Montelukast Sodium areas connected via the corpus callosum (Bütefisch et al., 2006, Lang et al., 2004 and Shimizu

et al., 2002). In the case of the ipsilesional left hemisphere, release from cortical inhibition in the setting of focal injury may facilitate activation of these areas during language tasks. Animal studies of cortical plasticity suggest that persistent recruitment of cortical areas during specific tasks may result in functional modifications that allow perilesional networks to engage more efficiently in the service of those tasks (Nudo & Friel, 1999). Activity-dependant plasticity, facilitated by ipsilesional disinhibition, may thus promote the recruitment and functional reorganization of perilesional regions of the left hemisphere to subserve language processing. While most evidence suggests that ipsilateral perilesional activation in chronic aphasic patients is associated with better language recovery, the role of right hemisphere recruitment during language tasks is more controversial.