Efficacy of Triple-daily 15mA tACS on Adolescent NSSI

NSSI injury severity will be assessed using items 5-10 of SITBI-R. Injury severity is rated on a five-point scale ranging from 1 (minimal injury) to 5 (severe injury requiring medical intervention), with higher scores indicating greater injury severity and worse clinical outcomes. Injury severity will be evaluated separately for the 7-day intervention period and the 4-week post-intervention follow-up period. The mean severity score across applicable NSSI events will be calculated separately for each period.

NSSI frequency will be assessed using SITBI-R. The outcome is defined as the total number of NSSI episodes occurring during the 7-day intervention period. The number of episodes ranges from 0 to no predefined maximum, with higher counts indicating more frequent NSSI behaviors and worse clinical outcomes.

Self-reported self-harm behaviors will be assessed using the 7-item version of the Deliberate Self-Harm Inventory (DSHI). Each item is rated on a 4-point scale: 0 (never), 1 (1-2 times), 2 (3-5 times), and 3 (6 or more times). Total scores range from 0 to 21, with higher scores indicating greater self-harm behavioral frequency burden and worse clinical outcomes.

Self-injury dependence will be assessed using the Ottawa Self-Injury Inventory (OSI), a self-report questionnaire evaluating dependence-related characteristics of NSSI, including urges to self-injure, difficulty controlling or stopping self-injury, and interference with daily functioning. The dependence-related section includes seven items rated on a five-point scale from 0 (never) to 4 (always). Total scores range from 0 to 28, with higher scores indicating greater self-injury dependence and worse clinical outcomes.

Momentary NSSI urge intensity will be assessed using a single item from the NSSI Urge and Resistance Efficacy Scale. Participants rate the intensity of their current urge to engage in NSSI on a 7-point scale ranging from 1 (no urge at all) to 7 (extremely strong urge or difficult to suppress). Higher scores indicate stronger NSSI urges and worse clinical outcomes.

Perceived ability to resist NSSI urges will be assessed using a single item from the NSSI Urge and Resistance Efficacy Scale. Participants rate their perceived ability to resist NSSI urges on a 7-point scale ranging from 1 (no ability to resist) to 7 (completely able to resist). Higher scores indicate greater perceived ability to resist NSSI urges and better clinical outcomes.

Self-efficacy in resisting NSSI urges will be assessed using the NSSI Urge and Resistance Efficacy Scale. Participants rate their confidence in resisting NSSI urges on a 7-point scale ranging from 1 (no confidence at all) to 7 (complete confidence). Higher scores indicate greater self-efficacy in resisting NSSI urges and better clinical outcomes.

Suicidal ideation severity will be assessed using the Beck Scale for Suicide Ideation (BSSI), a 19-item measure evaluating suicidal thoughts, wishes, and attitudes during the preceding week. Each item is scored from 0 to 2, yielding a total score ranging from 0 to 38. Higher scores indicate more severe suicidal ideation and worse clinical outcomes.

Depressive symptom severity will be assessed using the 24-item Hamilton Depression Rating Scale (HAMD-24), a clinician-rated instrument evaluating the severity of depressive symptoms. Total scores range from 0 to 76, with higher scores indicating more severe depressive symptoms and worse clinical outcomes.

Self-reported depressive symptom severity will be assessed using the 9-item Patient Health Questionnaire (PHQ-9). Each item is scored from 0 to 3, yielding a total score ranging from 0 to 27. Higher scores indicate more severe depressive symptoms and worse clinical outcomes.

Anxiety symptom severity will be assessed using the Hamilton Anxiety Rating Scale (HAMA), a 14-item clinician-rated instrument evaluating psychological and somatic symptoms of anxiety. Each item is scored from 0 to 4, yielding a total score ranging from 0 to 56. Higher scores indicate more severe anxiety symptoms and worse clinical outcomes.

Self-reported anxiety symptom severity will be assessed using the 7-item Generalized Anxiety Disorder scale (GAD-7). Each item is scored from 0 to 3, yielding a total score ranging from 0 to 21. Higher scores indicate more severe anxiety symptoms and worse clinical outcomes.

Emotion regulation difficulties will be assessed using the 16-item Difficulties in Emotion Regulation Scale (DERS-16), a self-report questionnaire evaluating difficulties in emotional awareness and clarity, acceptance of emotional responses, impulse control, and goal-directed behavior during emotional distress. Each item is rated on a 5-point scale from 1 (almost never) to 5 (almost always), yielding a total score ranging from 16 to 80. Higher scores indicate greater difficulties in emotion regulation and worse clinical outcomes.

Sleep quality will be assessed using the Pittsburgh Sleep Quality Index (PSQI), a self-report questionnaire evaluating sleep quality over the preceding month. The PSQI consists of seven components: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction. Each component is scored from 0 to 3, yielding a global score ranging from 0 to 21, with higher scores indicating poorer sleep quality.

Resting-state EEG recordings will be used to assess changes in neural oscillatory activity following active or sham transcranial alternating current stimulation (tACS). Spectral power will be quantified in prespecified frequency bands.

Resting-state EEG functional connectivity will be assessed using a prespecified connectivity metric between selected brain regions or electrode pairs. The connectivity metric and its reporting scale will be specified before analysis.

EEG spectral power will be assessed during the capsaicin-induced sensitization paradigm to characterize neural oscillatory activity associated with sustained experimentally induced pain. Spectral power will be quantified within predefined frequency bands.

ERP amplitudes will be assessed during the Cyberball social exclusion paradigm. EEG signals will be time-locked to predefined ball-tossing events, and amplitudes of prespecified ERP components will be quantified in microvolts (μV).

Heart rate will be derived from electrocardiographic (ECG) recordings and expressed in beats per minute (bpm). Higher values indicate a faster heart rate.

Heart rate variability (HRV) will be assessed using the root mean square of successive differences between normal-to-normal intervals (RMSSD), derived from ECG recordings. RMSSD will be expressed in milliseconds (ms) and used as an index of cardiac vagal modulation.

Somatosensory evoked potentials (SEPs) will be recorded to assess somatosensory cortical responses following active or sham transcranial alternating current stimulation (tACS). The amplitude of the early cortical N20 component will be quantified in microvolts (μV).

Pain intensity will be assessed every 5 minutes during the capsaicin-induced sensitization paradigm using a 0-10 visual analog scale (VAS) administered via PsychoPy. Peak pain intensity is defined as the maximum VAS score recorded during the session. Scores range from 0 (no pain) to 10 (worst imaginable pain), with higher scores indicating greater perceived pain intensity.

Assessed using the Post-Cyberball Questionnaire, administered immediately after the Cyberball paradigm (a 2-round, 3-minute per round, virtual ball-tossing game presented via PsychoPy). This measure includes two dimensions: Need Threat: Belonging, Self-esteem, Control, and Existence. Higher scores indicate greater perceived social need threat. Affective Response: Positive and Negative Affect. Higher negative affect scores indicate stronger negative emotions, higher positive affect scores indicate stronger positive emotions. A manipulation check is included to assess the perceived validity of the social exclusion.

Emotional responses to social exclusion will be assessed immediately after the Cyberball paradigm using the International Positive and Negative Affect Schedule - Short Form (I-PANAS-SF). This self-report questionnaire measures positive affect (PA) and negative affect (NA) on a 5-point Likert scale ranging from 1 (very slightly or not at all) to 5 (extremely). Higher PA scores indicate greater positive emotion, while higher NA scores indicate greater negative emotion. Changes in affective states will be analyzed to evaluate the emotional impact of Cyberball-induced social pain.

Emotion recognition accuracy will be assessed using an eye-region reading task. Participants will view images depicting different mental or emotional states and select the corresponding response. Accuracy will be calculated as the percentage of correct responses out of all valid trials, ranging from 0% to 100%. Higher scores indicate better recognition performance.

Eye-tracking recordings will be obtained during the eye-region reading task to assess visual attention and oculomotor behavior. Measures will include total fixation duration (milliseconds), fixation count (number of fixations), mean saccade amplitude (degrees of visual angle), and mean saccade velocity (degrees/second). These measures characterize different aspects of visual exploration and attentional processing.

Assessed on 7 treatment days. Includes frequency, type, and severity of any adverse events reported by participants during tACS sessions.

Overall subjective tolerability of transcranial alternating current stimulation (tACS) will be assessed using item 9 of the study-specific Subjective Tolerability Self-Assessment Questionnaire, administered after each treatment session during the 7-day intervention period. Participants rate their overall tolerability on a 5-point scale ranging from 1 (very poor) to 5 (very good). Higher scores indicate better subjective tolerability. The mean score across the 7 treatment days will be calculated for each participant.

Proportion of scheduled tACS sessions completed by each participant during the 7-day intervention period. Higher completion rate indicates better overall acceptability and adherence.