Role of subcortical structures in aphasia: evidence from studies of resting cerebral glucose metabolism

Abstract

Abstract Recent work has demonstrated the presence of aphasia with subcortical structural lesions including caudate, putamen, thalamus, and internal capsule. Divac and Öberg (Chapter 2, this volume) and Crosson (Chapter 12, this volume) have argued that the role of subcortical structures, and in particular the striatum and thalamus, is to act as part of a corticalsubcortical feedback loop which modulates, in a tonic manner, cortical function. Feedback loops are known to involve the frontal cortex, and the temporo-parietal cortex. Divac and Öberg argue for a multiple-tier organization of the forebrain with horizontal integration within a tier and vertical systems between the tiers. A vertical system consists of cortical-subcortical loops, that are focused around a specific thalamic nucleus. The basal ganglia are an integral part of some vertical systems. Divac and Öberg believe that the vertical systems mediate many types of complex behaviours. Language may be an exception by not being directly associated with the striatum. Crosson argues more specifically for cortico-striatal-thalamic loops, noting the existence of both anterior and posterior loops. He believes that these loops have a direct role in language. A critical question becomes whether it is disruption of these feedback systems that is important in subcortical aphasia, or whether (or to what extent) it is the intrinsic characteristics of the subcortical structures themselves that may play a role in the language abnormality.