Although there are reports in the early literature of lesions of the thalamus in association with disorders of perception, for example, Morsier's ( 1938) case of pulvinar lesion with "peduncular hallucinosis," as well as with disorders of cognition, such as Grunthal's ( 1942) case of "thalamic dementia," it was not until the monograph by Penfield and Roberts ( 1959) that attention was focused on the thalamus in relation to language organization. In this monograph, it was proposed that the thalamus, specifically the nucleus pulvinaris, was a way station in language processing between the anterior and posterior speech zones. While no persuasive evidence was presented in support of this hypothesis, it was at least consistent with the enormous expansion of pulvinar over the mammalian series leading to man, as well as with the presence of major fiber pathways between pulvinar and the posterior temporoparietal cortex.
Subsequently, the development of stereotactic surgery for the treatment of movement disorders, particularly for Parkinson's disease and dystonia, led to the investigation of psychological function following surgical lesion in various thalamic sites. In spite of the obvious importance of and interest in this region, it is striking how little we still know of the behavioral consequences of thalamic lesions in man. Unlike other areas, the thalamus is not often preferentially involved in neurological disease, nor is it commonly the site of localized vascular lesion. Surgical ablation has been carried out only in a few nuclear groups and only in subjects with preexisting neurological disorders, so that even there we see the effects on an ongoing pathological state rather than in a normal brain.
Nonetheless, over the last 20 years renewed interest in the role of the thalamus in language and cognition has given rise to new observations and experimental studies. It is the purpose of this chapter to review some of this material in relation to present concepts of language-brain relationships.____________________