The goal of this clinical study is to investigate the neural mechanisms of abnormal sensory phenomena in patients with Obsessive-Compulsive Disorder and to evaluate whether modulation of the insula-supplementary motor area circuit can improve these symptoms. The study will include adult patients with OCD (with or without sensory phenomena) and healthy volunteers.

The main questions it aims to answer are:

• Do patients with OCD show abnormal activity in the insula-SMA circuit compared with healthy controls?
• Is this abnormality associated with the presence and severity of abnormal sensory phenomena?
• Can low-frequency rTMS targeting the Supplementary Motor Area improve sensory phenomena and obsessive-compulsive symptoms? Researchers will compare an on-line rTMS group (viewing body-focused videos during stimulation) with an off-line rTMS group (resting during stimulation) to evaluate whether task engagement enhances treatment effects.

Participants will:

• Complete clinical assessments and behavioral tasks.
• Undergo EEG and fMRI assessments.
• Receive low-frequency rTMS targeting the Supplementary Motor Area.
• Repeat assessments after the intervention.

Phase 1:

This part adopts a cross-sectional design. A total of 30 patients with Obsessive-Compulsive Disorder with sensory phenomena, 30 OCD patients without sensory phenomena, and 30 healthy controls will be recruited. Clinical assessments will be conducted, including evaluation of the severity of sensory phenomena, as well as obsessive-compulsive, depressive, and anxiety symptoms. Resting-state functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) data will be collected. In addition, during a body-focused video task designed to activate the insula-SMA circuit, task-based fMRI-EEG data will be simultaneously acquired.

Phase 2:

This part adopts a randomized parallel controlled design. Based on the 30 OCD patients with sensory phenomena included in Phase 1, an additional 30 patients will be recruited, resulting in a total of 60 OCD patients with sensory phenomena. After completing baseline clinical scale assessments, behavioral tasks, fMRI, and EEG data collection, participants will be randomly assigned to an on-line group or an off-line group. Both groups will receive low-frequency repetitive transcranial magnetic stimulation (rTMS) targeting the Supplementary Motor Area for six consecutive days, with five sessions per day. In the on-line group, participants will watch body-focused sensory videos during each stimulation session, whereas the off-line group will remain at rest during stimulation. After completion of the intervention, clinical scale assessments, behavioral tasks, and fMRI and EEG data collection will be repeated.

Inclusion Criteria:

OCD with abnormal sensory phenomena

1. Meet the diagnostic criteria for Obsessive-Compulsive Disorder according to Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition.
2. Aged 18-55 years.
3. Score ≥16 on the Yale-Brown Obsessive Compulsive Scale, indicating moderate to severe symptoms.
4. Score >6 on the Sensory Phenomena Scale (SPS), indicating moderate to severe sensory phenomena.
5. Right-handed.
6. Either medication-free or on stable medication for at least 8 weeks.

OCD without abnormal sensory phenomena

1. Meet the diagnostic criteria for Obsessive-Compulsive Disorder according to Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition.
2. Aged 18-55 years.
3. Score ≥16 on the Yale-Brown Obsessive Compulsive Scale.
4. Score ≤6 on the Sensory Phenomena Scale (SPS).
5. Right-handed.
6. Either medication-free or on stable medication for at least 8 weeks.

Exclusion criteria

1. Meeting diagnostic criteria in Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition for psychiatric disorders other than OCD or obsessive-compulsive personality disorder.
2. OCD symptoms so severe that required assessments cannot be completed.
3. Presence of severe suicidal ideation or high suicide risk.
4. Pregnant women or women planning pregnancy in the near future.
5. History of epilepsy or any medical condition that may induce seizures or intracranial hypertension.
6. Contraindications to MRI, such as metallic implants.
7. Clinically significant medical illnesses or abnormal laboratory findings.
8. Inability to complete study procedures due to severe symptoms, low cognitive functioning, or poor cooperation.

Healthy Controls Inclusion criteria

1. No current or past psychiatric disorders meeting diagnostic criteria in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition.
2. Aged 18-55 years.
3. Right-handed. Exclusion criteria

1. Pregnant women or women planning pregnancy in the near future. 2. History of epilepsy or any medical condition that may induce seizures or intracranial hypertension.

3. Presence of severe suicidal ideation or high suicide risk. 4. Contraindications to MRI, such as metallic implants. 5. Clinically significant medical illnesses or abnormal laboratory findings. 6. Inability to complete study procedures due to severe symptoms, low cognitive functioning, or poor cooperation.