Parkinsonian deficits in serial multiarticulate movements for speech

Unlike the single joint arm movements so commonly the focus of Parkinson's disease (PD) studies, orofacial movements for speech are well-learned, complex motor sequences generated without visual guidance. The present study of upper lip, lower lip, and jaw movements during speech in PD was thus aimed at determining whether (1) PD speech kinematic deficits are comparable to those often observed in simpler limb movements; (2) coordination for multimovement actions such as speech is aberrant in PD, as recently claimed; and (3) the component muscle groups involved in this behaviour manifest uniform deficits. Results indicated that despite reduced amplitudes of jaw and upper lip displacement in PD subjects, all three of these oral movements were of normal duration. Secondly, PD lower lip movements manifested no deficits and bradykinesia (reduced velocity) was only found in movements of the jaw. Finally, there was an indication of movement coordination aberrations in these parkinsonian subjects. Overall, these results not only suggest a difference between orofacial and limb movement impairments in PD, but also document the need to broaden our perspectives on this movement disorder by examining a wider range of functional motor tasks.