Optimal Brain Targets for Enhancing Vocal Performance With Transcranial Direct Current Stimulation.

Abstract

Transcranial direct current stimulation (tDCS) can be used to temporarily and reversibly modulate brain functions and is an increasingly utilized tool to investigate the relationships between brain and behavior. This study aimed to identify the brain area where tDCS has the greatest effect on vocal quality, vocal range, neuromotor functioning of the larynx, and self-reported vocal effort in vocally healthy individuals. Sixteen adults, non-singers, with a mean age of 22.5 (±1.9) years and no vocal symptoms or brain dysfunction, participated in this double-blinded randomized crossover clinical trial. The participants underwent four anodal tDCS session (20 minutes; 2 mA) in targeting different areas-cerebellum, primary motor cortex (M1), primary somatosensory cortex (S1), and dorsolateral prefrontal cortex (DLPFC)-with a 7-day washout period between sessions. Volunteers were evaluated for vocal performance before and after each tDCS session. Voice recordings were taken to assess the following vocal parameters: vocal range profile (VRP) at weak and strong intensities; vocal quality (jitter, shimmer, irregularity, glottal-to-noise excitation ratio, and dysphonia acoustic index) at weak, habitual, and strong intensities; laryngeal diadochokinesis, and self-reported vocal effort using the adapted Borg CR10 scale. M1 stimulation enhanced the VRP by increasing maximum intensity and improving vocal quality, particularly at habitual and strong intensities. Similarly, S1 stimulation improved vocal quality at strong intensities but reduced the VRP by lowering the maximum fundamental frequency. Cerebellum stimulation enhanced neuromuscular control and coordination of the larynx without affecting vocal quality. Additionally, self-reported vocal effort decreased across all stimulated areas following tDCS. Our findings indicate that tDCS applied to different brain areas produces varying effects on vocal parameters.