This study aims to evaluate the feasibility and clinical outcome of the Exposure-based Cognitive-Behavioral Therapy (CBT) concurrent with Transcranial Alternating Current Stimulation (tACS) using individualized stimulation frequency in treating obsessive-compulsive disorder (OCD) patients, and explores the potential neural mechanisms of treatment effect by magnetic resonance imaging (MRI) and electroencephalography (EEG).

The current study aims to evaluate feasibility and clinical outcome of exposure-based CBT (ERP) combined with tACS over the prefrontal cortex (mPFC) in treatment of OCD patients. 62 OCD patients will be randomized into two groups (ERP+active tACS, ERP+sham tACS stimulation). All patients will be received 10 sessions of individual ERP in a two-month period, including 8 sessions of concurrent tACS with ERP (tACS+ERP). Based on the EEG parameters, individualized modeling was conducted to determine specific stimulation parameter schemes (stimulation frequency).

The treatment program consists of a total of 10 sessions, with the first and last sessions being psychological therapy only. The middle eight sessions will involve concurrent transcranial alternating current stimulation (tACS) and exposure and response prevention (ERP). The timing of assessments is designed to capture changes in symptom severity during the intervals between consecutive combined treatment sessions.

Three independent evaluators will assess the severity of patients' obsessive-compulsive symptoms using the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) at four time points:

Baseline assessment (prior to the start of treatment); After the first combined session (Session 2) and before the second combined session (Session 3); After the fourth combined session (Session 5) and before the fifth combined session(Session 6); After the eighth combined session (Session 9) and before the final treatment session (Session 10).

Patients will also undergo electroencephalography (EEG) assessments at each evaluation time point. The current study aims to explore whether the administration of individualized stimulation frequency tACS in conjunction with ERP can enhance the efficacy of ERP, providing early evidence for revealing the potential neural mechanisms underlying this treatment. Additionally, participants will undergo magnetic resonance imaging (MRI) scans at treatment baseline and after the completion of the full course of treatment.

The investigators recruited outpatient adults with OCD confirmed by the Mini-International Neuropsychiatric Interview (MINI). The following inclusion and exclusion criteria were also applied:

Inclusion Criteria:

• 18-60 years old
• With at least 9 years of education
• Y-BOCS score ≥16
• No history of serious medical, neurological illness or other psychotic disorders other than OCD (anxiety or mild to moderate depression secondary to OCD was not exclusionary)
• Medication-free or had received stable medication for at least 8 weeks before entering the study and continued the same medication throughout the study

Exclusion Criteria:

• History of serious medical, neurological illness or other psychotic disorders other than OCD
• OCD symptoms are severe, preventing the patient from completing the required assessment and examination
• Serious suicide risk
• Women who are pregnant or planning to become pregnant
• Currently taking antiepileptic medication
• Clinically significant physical illnesses or laboratory test abnormalities that have clinical significance
• Previous completion of a full course of CBT/ERP treatment