[Thalamic Aphasia: Viewing Language from the Thalamus].

Abstract

Aphasia resulting from cortical lesions typically manifests as a static impairment caused by the structural destruction of cortical language areas. In contrast, thalamic aphasia presents with contextually inappropriate speech, such as unrelated and morphemic paraphasias, and fluctuating symptoms across contexts and situations. This article integrates classical semiology with recent insights from systems and computational neuroscience to explain these phenomena. We introduce a framework in which the cerebral cortex serves as a comprehensive dictionary that stores phonological, lexical, and syntactic knowledge, whereas the thalamus acts as a dynamic filter for language production. The thalamus actively selects contextually appropriate words and suppresses irrelevant alternatives. Therefore, thalamic aphasia is explained as a breakdown in the dynamic, context-dependent control of cortical language networks. This approach translates computational principles into clinical phenomenology, thereby clarifying the distinct roles of the cortex and thalamus in language processing.