Clinical and Biological Correlates of Obsessive-Compulsive Disorder and Online Mindfulness-Based Cognitive Therapy

Patients with OCD. Inclusion Criteria: * Diagnosis of obsessive-compulsive disorder (OCD) according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) * Age between 18 and 45 years * Stable pharmacological treatment for at least 3 months prior to the start of the experimental intervention * No previous experience with mindfulness meditation, or previous mindfulness meditation experience with no practice during the 12 months prior to study enrollment * Ability and willingness to provide written informed consent. Exclusion Criteria: * Diagnosis of schizophrenia spectrum or other psychotic disorders, including schizoaffective disorder * Diagnosis of bipolar and related disorders * Major depressive disorder in an acute phase * Active substance use disorder or alcohol use disorder as the primary diagnosis * Personality disorders of clinically significant severity * Documented major neurocognitive disorder. Neurological conditions or medical conditions with a clinically significant impact on cognitive or mental functioning * Previous mindfulness meditation practice within the 12 months prior to study enrollment * Inability or unwillingness to provide informed consent Healthy subjects. Inclusion Criteria: * Age between 18 and 45 years, with age matching within a maximum difference of ±3 years from the corresponding index patient. In all cases, control participants must be at least 18 years and no older than 48 years * Voluntary participation in the study. * Ability and willingness to provide written informed consent Exclusion criteria: * Age younger than 18 years * History of psychiatric disorders, as assessed using the Structured Clinical Interview for DSM-5 Disorders - Clinician Version (SCID-CV) * Intellectual developmental disorder. * Current substance use disorder or alcohol use disorder * Neurological disorders, including Parkinson's disease, major neurocognitive disorders, neurodegenerative syndromes, ataxias, multiple sclerosis, cerebrovascular events (stroke or transient ischemic attack \[TIA\]), central nervous system neoplasms, epilepsy, history of seizures, or clinically significant tremor * Systemic medical conditions (e.g., diabetes mellitus, atherosclerosis, chronic arterial hypertension, or malignancies) requiring pharmacological treatment * Current or previous mindfulness meditation practice within the 12 months prior to study enrollment