Speech and Voice Outcomes Following HD-tDCS Over the Left SMA

Parkinson's disease (PD) is a movement disorder that affects more than one million individuals in the United States. Over 90 percent of individuals with PD manifest speech and voice impairments in the course of their disease, which can significantly compromise patients' quality of life. While pharmaceutical intervention and deep brain stimulation reliably improve the cardinal motor symptoms of PD, such as tremor, rigidity, and bradykinesia, the effects of these treatments on speech and voice are inconsistent, with some studies showing the exacerbation of pre-treatment deficits. This inconsistency often occurs because treatments are calibrated to ameliorate limb motor symptoms, with no direct optimization to improve speech and voice functions. However, there is no established non-invasive neurostimulation protocol for communication disorders in PD. Increasing evidence supports the application of non-invasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) to improve both motor and non-motor symptoms in PD. However, limited evidence exists regarding the application of tDCS to improve speech and voice disorders in PD. Moreover, there is no established long-term effect of tDCS on speech and voice deficits in PD. In this proposed study, we will address these gaps by investigating the immediate and short-term effects of high definition-transcranial direct current stimulation (HD-tDCS) over the left supplementary motor area (SMA) on speech and voice deficits in 24 PD and 24 matched control participants.