Safety and Acute Effects of tDCS on Vocal Performance in Adolescent Singers

Participants will receive a single 20-minute session of active transcranial direct current stimulation (tDCS) at 2.0 mA using 5 × 7 cm electrodes, with the anode positioned over C5 to target the left laryngeal primary motor cortex and the cathode positioned over the right supraorbital region.

Participants will receive a single session of active transcranial direct current stimulation (tDCS). The anode will be positioned over C5, targeting the left laryngeal primary motor cortex, and the cathode over the right supraorbital region using 5 × 7 cm electrodes. Current will be gradually increased to 2.0 mA, maintained for 20 minutes, and gradually reduced at the end of stimulation.

Participants will receive a single 20-minute sham tDCS session using the same electrode montage as the active condition. Sham stimulation will reproduce the initial sensations associated with tDCS through an initial ramp-up and brief stimulation period, without sustained current delivery.

Participants will receive a single sham transcranial direct current stimulation (tDCS) session using the same electrode montage as the active condition, with the anode positioned over C5 and the cathode over the right supraorbital region using 5 × 7 cm electrodes. An initial ramp-up and brief stimulation period will reproduce the initial sensations associated with tDCS, followed by discontinuation of sustained current. The sham session will have the same overall duration as the active session.

Treatment-emergent adverse events will be assessed using a structured checklist documenting the presence and intensity of tingling/itching, warmth or burning sensation, skin redness, headache, dizziness, nausea, fatigue or drowsiness, visual symptoms, and other spontaneously reported symptoms. Symptoms present at baseline will be recorded, and an event will be considered treatment-emergent if it occurs after the start of stimulation or increases in intensity relative to baseline.

For each event, severity will be categorized as none, mild, moderate, or severe. Stimulation interruptions, inability to complete the stimulation session, and adverse events requiring additional assessment or care will also be recorded. The number and proportion of participants experiencing each treatment-emergent adverse event, together with its severity, will be reported.

Vocal performances will be audiovisually recorded and evaluated by blinded independent expert raters using an adapted analytical vocal-performance rubric based on Gynnild (2015). The rubric evaluates Technique, Language/Text, Musicality, Ability to Communicate, and Choice of Repertoire. Performance grades range from A to F and are converted to numerical values from 5 to 0, with higher scores indicating better vocal performance. Because all participants perform the same standardized repertoire, the Choice of Repertoire domain will not contribute to the primary performance score. The primary vocal-performance score will be calculated as the mean of the four applicable domain scores (Technique, Language/Text, Musicality, and Ability to Communicate), each scored from 0 to 5, resulting in an overall mean score ranging from 0 to 5. Higher scores indicate better vocal performance. Changes over time will be compared between the active and sham groups.

Vocal performances will be audiovisually recorded and evaluated by blinded independent expert raters using an adapted analytical vocal-performance rubric based on Gynnild (2015). The rubric evaluates technique, language/text, musicality, ability to communicate, and choice of repertoire. Performance grades range from A to F and are converted to numerical values from 5 to 0, with higher scores indicating better vocal performance. Because all participants perform the same standardized repertoire, the choice-of-repertoire domain will not contribute to the primary performance score. The primary vocal-performance score will be calculated from the applicable rubric domains, and changes over time will be compared between the active and sham groups.

Participants will rate their own vocal performance on a numerical rating scale from 0 to 10, where 0 represents the worst possible performance that day and 10 represents the best possible performance that day. Higher scores indicate better self-perceived vocal performance.

Participants will rate their nervousness related to the vocal performance on a numerical rating scale from 0 to 10, where 0 represents no nervousness and 10 represents the highest level of nervousness experienced. Higher scores indicate greater self-reported nervousness.

Participants will rate their confidence regarding the vocal performance on a numerical rating scale from 0 to 10, where 0 represents no confidence and 10 represents the highest possible confidence. Higher scores indicate greater self-reported confidence.

Participants will report whether they believe they received active stimulation, sham stimulation, or whether they do not know which condition they received. Responses will be used to evaluate the effectiveness of participant blinding.

Completion rate will be calculated as the proportion of enrolled participants who complete all planned study procedures, including baseline assessment, the assigned tDCS or sham session, immediate post-intervention assessment, and the 2-hour post-intervention assessment. The number and percentage of participants completing the full study protocol will be reported.

Protocol adherence will be assessed as the proportion of enrolled participants who complete the assigned stimulation session and all planned study assessments according to the predefined protocol without major protocol deviations. The number and percentage of participants with complete adherence will be reported, and protocol deviations will be documented.