Purpose:
This study aims to evaluate the effectiveness of an accelerated intermittent Theta Burst Stimulation (iTBS) protocol-a non-invasive brain stimulation technique-targeted at the dorsomedial prefrontal cortex (dmPFC) and anterior cingulate cortex (ACC) in patients with treatment-resistant Obsessive-Compulsive Disorder (OCD). Additionally, the study seeks to identify electrophysiological biomarkers (such as EEG microstates and heart rate variability) that may predict which patients are most likely to benefit from the treatment.
Methodology:
The study will include 30 patients aged 18-65 diagnosed with OCD according to DSM-5 criteria who have not responded sufficiently to standard treatments. Participants will undergo an intensive 7-day treatment program consisting of 4 iTBS sessions per day (totaling 28 sessions). Clinical symptoms will be assessed before and after the treatment using standardized scales, including the Yale-Brown Obsessive Compulsive Scale (Y-BOCS), Hamilton Depression Rating Scale (HAM-D), and Hamilton Anxiety Rating Scale (HAM-A). Resting-state EEG measurements and heart rate data will be recorded during and after the sessions to analyze physiological changes.
Goal:
The findings are expected to contribute to the development of personalized neuromodulation protocols and help identify predictors of treatment response for OCD patients.
Being between 18 and 65 years of age.
Being diagnosed with Obsessive-Compulsive Disorder (OCD) according to DSM-5 criteria.
Non-responsiveness to at least one Selective Serotonin Reuptake Inhibitor (SSRI) treatment at an adequate dose and duration.
Having a Y-BOCS score of ≥20 following the initial evaluation.
Severe neurological disorders or neurodegenerative diseases.
Any condition associated with increased seizure risk
History of cochlear implants, metal implants in the head and neck area, cardiac pacemakers, deep brain stimulation, or vagus nerve stimulation.
History of neurosurgical intervention.
Single group
iTBS TMS
DeviceAccelerated intermittent Theta Burst Stimulation (iTBS) will be delivered using a MagVenture MagPro R30 stimulator with a Cool D-B80 double cone coil. The stimulation is targeted at the dorsomedial prefrontal cortex (dmPFC) and anterior cingulate cortex (ACC), specifically 25.8% anterior of the nasion-inion distance. The treatment will be applied at 100% of the motor threshold, which is determined via the Extensor Hallucis Longus muscle. The protocol consists of an intensive 7-day program with 4 sessions per day, totaling 28 sessions. Each session delivers 1,800 pulses and lasts approximately 9 minutes. Patients will continue their stable dose of Selective Serotonin Reuptake Inhibitors (SSRIs) throughout the study.
Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) Total Score
The Y-BOCS is a 10-item clinician-administered scale used to assess the severity of obsessive-compulsive symptoms. Each item is rated from 0 to 4. The total score ranges from 0 to 40, where higher scores indicate greater symptom severity (32-40: extreme, 24-31: severe, 16-23: moderate, 8-15: mild, 0-7: subclinical).
EEG Microstate Analysis Parameters
Resting-state EEG data will be analyzed using the MICROSTATELAB v2.1 extension for EEGLAB focusing on the four canonical microstate classes labeled A, B, C, and D. For each participant, four specific spatio-temporal parameters will be calculated to evaluate neural dynamics. These include Mean Duration which measures the average lifespan of a specific microstate in milliseconds to represent the stability of neural generators, and Occurrence which measures the average frequency of each microstate per second in Hz to reflect activation tendencies. Additionally, Time Coverage will be calculated as the percentage of total analysis time during which a specific class is dominant, and Transition Probability will be determined to show the likelihood of one microstate class transitioning into another, providing insight into the sequential activation dynamics of the underlying neural networks.
Frontal-Vagal Activity via Heart Rate Deceleration (HRD)
Heart rate data will be recorded using a Polar H10 sensor during iTBS sessions. HRD will be calculated as the change in heart rate (beats per minute - bpm) during the stimulation period compared to the pre-stimulation baseline. Lower heart rate (greater deceleration) is investigated as a predictor of higher fronto-vagal activation and treatment response.
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