The effect of subthalamic nucleus deep brain stimulation on speech metrics in Parkinson's disease

Speech impairment frequently occurs in Parkinson's disease (PD). The sequence effect, progressive deterioration in speed or amplitude of ongoing movement, is unique to PD and does not respond well to dopaminergic therapy. While subthalamic nucleus deep brain stimulation (STN DBS) can improve various motor symptoms in PD, its impact on speech and the speech sequence effect remains unclear. Here, we investigated the effects of STN DBS on speech metrics including the sequence effect in people with PD.

Fifteen individuals with PD who underwent bilateral STN DBS surgery participated in this study. We utilized the sustained phonation (SP) test and the diadochokinetic (DDK) test, which were performed under both OFF and ON stimulation conditions. Primary outcome measures included total SP duration, mean intensity, DDK rates, and the speech sequence effect.

STN DBS significantly improved the duration of SP without altering mean intensity. It also improved the rate of DDK syllable production for /pa/. However, it did not significantly change the speech sequence effect.

These findings indicate that while STN DBS can enhance certain speech parameters, it does not significantly mitigate the speech sequence effect. Further studies incorporating more comprehensive and functional speech assessment are needed to better understand the broader impact of DBS on speech and guide personalized treatment strategies for speech impairment in PD.