This study compares two types of non-invasive brain stimulation to treat major depression in patients who have not found relief from at least one antidepressant medication.

The study will use a specific type of brain stimulation called prolonged intermittent Theta Burst Stimulation (piTBS). The standard way to use piTBS for depression is to target an area on the side of the head called the dorsolateral prefrontal cortex (DLPFC). This study will compare this standard piTBS method with a newer approach, deep piTBS, which targets a different, deeper area in the middle of the brain called the anterior cingulate cortex (ACC).

Participants will be randomly assigned to one of two groups. One group will receive the deep piTBS treatment, and the other will receive the standard piTBS treatment. Both treatments are given once a day, five days a week, for four weeks. The study aims to find out if the deep piTBS approach is more effective at reducing symptoms of depression than the standard approach. Researchers will also look at effects on anxiety and other related symptoms.

Background:

Major depressive disorder (MDD) is associated with dysfunction in large-scale brain networks, including the central executive network (CEN), default mode network (DMN), and the salience network (SN). The anterior cingulate cortex (ACC) is a key hub in the SN, and its dysfunction is believed to be a core pathological feature of depression. While high-frequency repetitive transcranial magnetic stimulation (rTMS) over the left dorsolateral prefrontal cortex (DLPFC) is an evidence-based treatment for treatment-resistant depression (TRD), it only indirectly modulates deeper structures like the ACC. Deep TMS techniques using a double-cone coil can directly stimulate deeper regions such as the medial prefrontal cortex (mPFC) and ACC, which may offer a more direct and potentially more effective therapeutic approach. Intermittent theta burst stimulation (iTBS) is a newer form of rTMS that significantly shortens treatment time, but its application to deep brain targets like the ACC has not been well-studied.

Objective:

This study aims to compare the therapeutic efficacy of prolonged intermittent theta burst stimulation (piTBS) targeting the ACC (deep piTBS) versus the standard protocol targeting the left DLPFC (standard piTBS) for patients with TRD. The study will also evaluate the effects of these interventions on comorbid anxiety, obsessive-compulsive, and somatic symptoms, as well as on physiological indicators.

Study Design:

This is a single-center, block-randomized study. A maximum of 90 participants meeting DSM-5 criteria for major depressive disorder, who have failed to respond to at least one adequate trial of an antidepressant, will be recruited. Participants will be randomly assigned in a 2:1 ratio (deep piTBS: standard piTBS, within blocks of six) to one of two treatment arms:

Deep piTBS Group: Participants will receive stimulation targeting the ACC using a double-cone coil. Stimulation intensity will be set at 90% of the resting motor threshold (rMT) determined from the tibialis anterior muscle.

Standard piTBS Group: Participants will receive stimulation targeting the left DLPFC using a standard figure-8 coil. Intensity will be set at 90% of the rMT determined from the abductor pollicis brevis muscle.

For both groups, the piTBS protocol consists of 1800 pulses per session, delivered daily (5 days/week) for 4 weeks, for a total of 20 sessions.

Outcome Measures:

The primary outcome is the change in the 17-item Hamilton Depression Rating Scale (HAM-D17) score from baseline to the end of treatment (after 20 sessions). Secondary outcomes include changes in scores on the Hamilton Anxiety Rating Scale (HAM-A), Yale-Brown Obsessive Compulsive Scale (Y-BOCS), Patient Health Questionnaire-15 (PHQ-15), Beck Depression Inventory-II (BDI-II), Beck Anxiety Inventory (BAI), and various physiological measures including heart rate variability (HRV). Assessments will be conducted at baseline, after every 5 treatment sessions, and one week after the completion of the 20th session.

Inclusion Criteria:

• Ages between 18 and 70 years, inclusive.
• Diagnosis of Major Depressive Disorder (MDD) with a current major depressive episode, according to DSM-5 criteria, as confirmed by a psychiatrist.
• History of inadequate response to at least one trial of an antidepressant medication of adequate dose and duration.
• A score of 18 or greater on the 17-item Hamilton Depression Rating Scale (HAM-D17) at the screening visit.

Exclusion Criteria:

• Lifetime diagnosis of any primary psychotic disorder (e.g., schizophrenia spectrum disorders) or bipolar and related disorders according to DSM-5.
• Significant current suicide risk, as indicated by a score of 4 on item 3 of the HAM-D17.
• Current substance use disorder (excluding tobacco) within the last 3 months, according to DSM-5.
• Presence of significant cognitive impairment, such as intellectual disability, delirium, or a diagnosed neurocognitive disorder.
• Any personal history of seizures, stroke, brain tumor, brain aneurysm, increased intracranial pressure, or other major neurological disorders.
• Presence of metal implants in the head (excluding dental fillings) or any implanted medical devices such as a cardiac pacemaker or defibrillator.
• Currently pregnant.
• Any other major medical condition that, in the investigator's judgment, could compromise participant safety or interfere with the study procedures.

The raters for the primary and key secondary outcome scales (including HAM-D17, HAM-A, YMRS, and Y-BOCS) are blinded to the participant's treatment allocation.