Subcortical aphasia: Evidence from stereotactic surgical lesions

The cerebral cortex has traditionally been considered the neural substrate of language. But this traditional view has been challenged by the findings of a proliferating number of clinico-neurological correlation studies that have noted the occurrence of language disorders in association with apparently subcortical lesions. The introduction of new neuroradiological methods for lesion localization in vivo, including computed tomography (CT) and more recently magnetic resonance imaging (MRI), has led to an increasing number of reports in the literature of aphasia following apparently purely subcortical lesions involving the striato-capsular region and/or thalamus. One outcome of the reported clinico-neuroradiological correlation studies has been the development of a number of theories regarding the function of subcortical structures in language. These theories, largely developed on the basis of speech and language data collected from subjects who have had cerebrovascular accidents involving the thalamus or striatocapsular region, have been expressed as neuroanatomically-based language model. The chapter investigates the effect of surgically induced lesions of the globus pallidus on language functioning, utilizing a comprehensive linguistic assessment battery; discusses post-operative language profiles in relation to operative theoretical models of subcortical participation in language; and validate or nullify the hypothesis of a corticostriato-pallido-thalamo-cortical loop subserving language, which promotes functionally distinct roles for the globus pallidus and thalamus.