The thalamus and aphasia, including transcortical aphasia: a review.

Left thalamic lesions can produce motor speech disturbances: disorders of articulation and of phonation. Left thalamic lesions can also produce aphasic disorders: word-emission difficulties; difficulties with comprehension, reading, writing, and arithmetic; and sometimes suppression of conversational propositional speech with preservation of nonpropositional repetitional or automatic speech. The relative preservation of nonpropositional speech justifies the assignment of such cases of thalamic aphasia to the category of transcortical aphasia (TA). Also included in TA are aphasias from dominant hemisphere supplementary motor region (SMR) lesions. In this context the suggestion by Penfield and Roberts that the thalamus and the SMR interact via the pedunculus thalami superior is noted.