The right place at the right time?

Abstract

Language functions that are disrupted by focal lesions in the left hemisphere often recover substantially over time. It has long been hypothesized that the right hemisphere gradually assumes language functions that have been impaired by left hemisphere lesions. This hypothesis has received support from a variety of sources. Individuals who recover from aphasia after stroke often become aphasic again after right hemisphere lesions (Nielson, 1946; Levine and Mohr, 1979) or after sodium amytal injection in the right carotid artery (Kinsbourne, 1971), consistent with the hypothesis that language had ‘crossed’ to the right hemisphere. Likewise, functional neuroimaging studies have often revealed more activation in the right hemisphere during language tasks in recovered aphasic patients compared to healthy controls (Weiller et al ., 1995; Ohyama et al ., 1996; Cappa et al ., 1997; Musso et al ., 1999; Thulborn et al ., 1999; Thompson et al ., 2000; Leff et al ., 2002; Crinon and Price, 2005). However, other functional imaging studies have revealed increased perilesional activation in the left hemisphere during language tasks compared to normal controls (Karbe et al ., 1995; Heiss et al ., 1999; Warburton et al ., 1999; Thiel et al ., 2001). Furthermore, several PET and fMRI studies have demonstrated that the degree of activation in right hemisphere areas (or perilesional left hemisphere areas) does not correlate with the degree of recovery (Heiss et al ., 1999; Cardebat et al ., 2003). A brief review of the literature on functional imaging studies of recovery of any function after stroke reveals that some studies show increased activation with improved function (e.g. Kessler et al ., 2000; Thompson et …