The Effects of Deep Brain Stimulation on Speech Motor Control in People With Parkinson's Disease.

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Despite the overall benefits of deep brain stimulation (DBS) in Parkinson's disease (PD), its effects on speech production have been mixed when examined using auditory-perceptual and acoustic measures. This study investigated the effects of DBS on the lip and jaw kinematics during sentence production in individuals with dysarthria secondary to PD. Twenty-seven participants from three groups were included in the study: (a) individuals with PD and without DBS (PD group), (b) individuals with PD and with DBS (PD-DBS group), and (c) neurologically healthy control speakers (HC group). Lip and jaw movements during speech were recorded using optical motion capture and analyzed for path distance, speed, duration, articulatory stability, and interarticulator coordination. The PD-DBS group showed (a) increased path distance compared with the PD and HC groups and (b) increased speed compared with the PD group but not the HC group. Both PD and PD-DBS groups exhibited lengthened sentence duration compared with the HC group. Articulatory stability was greater for the two PD groups, PD and PD-DBS, compared with the HC group. Spatial, but not temporal, coordination was lower for the PD group than for the other two groups. The only kinematic changes between the DBS on and off conditions within the PD-DBS group were increases in spatial coordination. These data suggest that DBS primarily affects the amplitude scaling of articulatory movements, but not the temporal scaling, in individuals with PD. The findings are discussed with respect to the DBS-induced neural changes and their effects on speech motor control in PD.