Others have argued that functional activation of right hemisphere areas in aphasic patients during language tasks is epiphenomenal, and neither facilitates nor hinders language recovery
(Thiel et al., 2001). The notion that the right hemisphere may play a facilitative role in language recovery after left hemisphere stroke dates as far back as the late 19th century. Barlow (1877) described the case of a 10-year old boy who lost but then recovered the capacity for speech after a left hemisphere stroke, only to lose it again after acquiring a second, right-hemisphere lesion (Finger, Buckner, & Buckingham, 2003). Other reported cases have shown that new right-hemisphere mTOR inhibitor lesions acquired after functional recovery in aphasia can cause deterioration of language (Basso et al., 1989, Gainotti, 1993 and Gowers, 1887). Amobarbital studies have demonstrated that for healthy right-handed adults, language functions are suspended after left-sided carotid injections; however, for aphasic patients
with extensive left hemisphere strokes, residual speech may be suspended by right- and not left-sided carotid injections (Kinsbourne, 1971). Furthermore, some patients who have undergone surgical left hemispherectomy have shown substantial language recovery (Vargha-Khadem et al., 1997) indicating that the right hemisphere possesses the capacity to process language information in the absence of a functioning left hemisphere. It has been proposed that the capacity for language processing exists in right hemisphere regions that are homotopic to left hemisphere perisylvian structures, but is usually masked by transcallosal interhemispheric GDC-0199 research buy inhibition from the dominant left-hemisphere (Karbe, Thiel, Weber-Luxenburger, Herholz, et al., 1998). According before to this hypothesis, language recovery after left hemisphere stroke is associated with a release from inhibition of latent, right-hemisphere language functions. A number of neuroimaging studies involving language tasks have revealed that there is, in addition to activation of left hemisphere language regions, robust activation in homotopic right hemisphere regions
after left hemisphere stroke (Basso et al., 1989, Buckner et al., 1996, Gold and Kertesz, 2000, Ohyama et al., 1996, Rosen et al., 2000, Warburton et al., 1999 and Weiller et al., 1995). We recently pursued an investigation of fMRI and PET studies in patients with aphasia using Activation Likelihood Estimation (ALE) meta-analysis in which we analyzed 240 activation foci from 104 aphasics, and 197 foci from 129 controls (see Fig. 1). We found that performance on language production tasks in aphasic patients is reliably associated with activation of regions in the right inferior frontal gyrus, whereas comprehension tasks are associated with activation of the right middle temporal gyrus (Turkeltaub, Messing, Norise, & Hamilton, submitted for publication).