Amygdala-Targeted Transcranial Temporal Interference Stimulation for Major Depressive Disorder: A Randomized Sham-Controlled Trial of Clinical Efficacy and Neurobiological Mechanisms

Active transcranial temporal interference stimulation (tTIS) will be delivered using two pairs of scalp electrodes. Two high-frequency alternating currents with slightly different carrier frequencies will be applied to generate a low-frequency temporal interference envelope within the targeted amygdala region. Electrode placement and stimulation parameters will be determined according to the study protocol and individualized electric-field modeling when applicable. Participants assigned to the active group will receive 10 stimulation sessions, with each session lasting 30 minutes, according to the predefined treatment schedule.

Participants assigned to the sham group will undergo the same electrode placement and treatment procedures as the active stimulation group. Sham stimulation will include brief ramp-up and ramp-down periods to mimic the initial sensory experience of active stimulation, without delivering continuous therapeutic stimulation during the remainder of the session.

The 17-item Hamilton Depression Rating Scale (HAMD-17) is a clinician-rated scale used to assess the severity of depressive symptoms. Total scores range from 0 to 52, with higher scores indicating greater depressive symptom severity. The primary outcome is the change in HAMD-17 total score from baseline to the end of the 10-session intervention.

The Montgomery-Åsberg Depression Rating Scale (MADRS) is a clinician-rated scale used to assess the severity of depressive symptoms. Total scores range from 0 to 60, with higher scores indicating greater depressive symptom severity. Changes in MADRS total score from baseline will be assessed following treatment and during follow-up.

The Hamilton Anxiety Rating Scale (HAMA) is a clinician-rated scale used to assess the severity of anxiety symptoms. Total scores range from 0 to 56, with higher scores indicating greater anxiety severity. Changes in HAMA total score from baseline will be assessed following treatment and during follow-up.

The Snaith-Hamilton Pleasure Scale (SHAPS) is used to assess anhedonia and reduced capacity to experience pleasure. Changes in SHAPS score from baseline will be used to evaluate treatment-related changes in hedonic functioning.

The Pittsburgh Sleep Quality Index (PSQI) is a self-reported measure of sleep quality and sleep disturbances. The global score ranges from 0 to 21, with higher scores indicating poorer sleep quality. Changes in PSQI global score from baseline will be assessed following treatment and during follow-up.

The WHOQOL-BREF is a self-reported measure of quality of life across physical health, psychological health, social relationships, and environmental domains. Higher domain scores indicate better perceived quality of life. Changes in domain scores from baseline will be assessed after treatment and during follow-up.

The Generalized Anxiety Disorder-7 (GAD-7) is a self-reported measure of anxiety symptoms. Total scores range from 0 to 21, with higher scores indicating greater anxiety symptom severity. Changes in GAD-7 score from baseline will be assessed following treatment and during follow-up.

The Patient Health Questionnaire-9 (PHQ-9) is a 9-item self-reported measure used to assess the severity of depressive symptoms. Total scores range from 0 to 27, with higher scores indicating greater depressive symptom severity. Changes in PHQ-9 total score from baseline will be assessed following treatment and during follow-up.

The THINC-integrated Tool (THINC-it) is a computerized cognitive assessment designed to evaluate subjective and objective cognitive functioning, including attention, processing speed, working memory, and executive function. Changes in THINC-it performance from baseline will be assessed following treatment and during follow-up.

The Temporal Experience of Pleasure Scale (TEPS) is a self-reported measure of anticipatory and consummatory pleasure. Changes in TEPS scores from baseline will be explored to assess treatment-related changes in reward-related emotional experience.

The Emotion Regulation Questionnaire (ERQ) assesses habitual use of cognitive reappraisal and expressive suppression as emotion regulation strategies. Changes in ERQ scores from baseline will be explored following treatment and during follow-up.

Diffusion tensor imaging (DTI) will be used to explore treatment-related changes in white matter microstructural measures within neural pathways associated with the amygdala and emotion-regulation networks.

Functional magnetic resonance imaging (fMRI) will be used to assess treatment-related changes in functional connectivity involving the amygdala and brain regions associated with emotional processing and regulation. Amygdala-based functional connectivity measures will be compared across study time points.