Verbal short-term store-rehearsal system and the cerebellum - Evidence from a patient with a right cerebellar lesion

We describe an 18-year-old patient who underwent surgical removal of the ri ght cerebellar hemisphere for the presence of a neoplastic lesion. After su rgery, the patient's neuropsychological examination was normal except for a transient selective verbal short-term memory (STM) impairment characterize d by reduced verbal digit span and rapid forgetting of verbal material. An extensive examination of the patient's deficit was performed in order to id entify which of the two components of STM (phonological short-term store an d/or rehearsal system) was impaired. The functional locus of the deficit wa s identified at the level of the phonological output buffet; a component of the rehearsal system, as suggested by the pattern of results obtained, nam ely; the improvement of the digit span seen with pointing compared with the verbal response; the advantage of auditory over visual presentation of dig its; and the lack of a phonological-similarity effect with visual presentat ion of letters. On the other hand, the functioning of the phonological stor e was demonstrated by the normal amplitude of the recency effect in free re call of words and by the phonological-similarity effect with auditory prese ntation of letters. Our finding is consistent with previous functional (PET ) studies showing the involvement of the right cerebellum during tasks requ iring silent recirculation of verbal information. We conclude that the cere bellum takes part in the planning of speech production at a level that does not require an overt articulation.