Transcortical aphasia. Importance of the nonspeech dominant hemisphere in language repetition

While a relative preservation of repetition in acute transcortical aphasia (TA) has usually been associated with the functional integrity of the speech dominant (left) perisylvian area, recent amytal data (Bando et al., 1986) have suggested a fundamental role of the nondominant (right) hemisphere in language repetition. The neuroradiological correlates of repetition were studied in a consecutive series of 21 patients with acute TA. A similar frequency of either perisylvian or extraperisylvian pathology was found. In 2 patients with perisylvian pathology, the injection of amytal in the hemisphere contralateral to the lesion abolished repetition. Positron emission tomography (PET) in another patient revealed marked hypometabolism over the entire left cortical mantle ipsilateral to a basal ganglia lesion, suggesting that preserved repetition was carried out by right hemisphere structures. This was confirmed in a second patient with left extraperisylvian pathology, in whom a second lesion in the right hemisphere resulted in impaired repetition. These findings suggest that the spared contralateral hemisphere may subserve residual repetition in some transcortical aphasic patients with a lesion within or outside the speech-dominant perisylvian area.