Speech Changes After Transcranial Direct Current Stimulation in Individuals Diagnosed With Parkinson's Disease

Abstract

Purpose: Parkinson's disease (PD) is a progressive neurological disease that results in motor and cognitive impairments, including impaired speech production. Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique that shows promise in improving limb motor skills and executive function in individuals with PD. The aim of this study was to examine the impact of tDCS on speech production in individuals diagnosed with PD. Method: Six males, aged 65–78 years, with a diagnosis of PD, participated in a double-blinded controlled crossover study to assess the immediate effects of tDCS to the premotor cortex on speech production. Auditory–perceptual (Consensus Auditory–Perceptual Evaluation—Voice) and acoustic voice outcomes (e.g., fundamental frequency, intensity, noise-to-harmonic ratio [NHR], and speech rate) were gathered pre- and post-anodal simulation and sham conditions. Measures were compared across times and conditions. Results: Speech rate was below normative levels for all participants prior to tDCS. Speech rate increased significantly in conversation following stimulation but not sham conditions and exceeded normative values for two participants. NHR increased following stimulation. No significant difference in other perturbation measures, perceptual ratings, fundamental frequency, or intensity were noted. Conclusions: All participants completed the protocol without discomfort. The observed increase in speech rate needs to be interpreted in the context of excitation resulting from neurostimulation using tDCS.