The contribution of apraxic speech to working memory deficits in Parkinson's disease

This article links two formerly separate areas of research associated with Parkinson's disease (PD): speech and memory. It is proposed that speech def icits occur in PD not merely at the level of muscular control, as is common ly termed dysarthria, but also at the level of speech planning and programm ing, more aptly described as a form of apraxia. It is further argued that P D patient groups exhibit small deficits in verbal span, and the link betwee n apraxic speech and verbal span is elucidated via Baddeley's (1986) model of working memory. An experiment is described in which aspects of speech of 36 PD and 43 healthy control subjects were rated and classified, and measu res of span and articulation rate for words of different syllable lengths w ere taken. Twenty-three PD subjects had dysarthric speech, while 14 of them had apraxic speech, which was associated with lower memory span scores for longer words. It is concluded that apraxic speech can be a source of reduc ed memory span in PD. In addition to implications for rehabilitation and th erapeutic work with PD sufferers, these findings advance our theoretical un derstanding of the Parkinsonian syndrome. (C) 2000 Academic Press.