Obsessive compulsive Disorder (OCD) is a frequent psychiatric disorder. Obsessions and compulsions are the two manifestations of this disease. Obsessions are recurrent anxious ideas, and compulsions repetitive behavior aiming to decrease this anxiety.

OCD symptoms have been associated with cortical and sub-cortical dysfunctions and more precisely an hyperactivity of prefrontal cortex / basal ganglia loops.

Functional neuro-imagery studies have shown a significant decrease of orbito-frontal cortex, anterior cingulate cortex, caudate nucleus and cerebellum activities after two OCD reference treatments : medication and Cognitive and Behavioral Therapy (CBT).

Two groups of 20 patients are included in this study and follow a CBT for 15 sessions. They are randomised in two groups : one proposing a "reference CBT", the other associate CBT to a new psychopedagogic task developed by the investigators team.

Clinical investigations and neuro-imagery data are collected at the main steps of therapies : before, during (half-therapy), at the end of therapies and 6 month later. Symptoms severity, patients and relatives quality of life are also assessed.

Inclusion Criteria:

• Age between 18 and 65;
• Following Obsessive Compulsive Disorder criteria according to DSM IV(300.3 ;MINI 5.0.0);
• OCD severity range from 20 to 30 on the Y-Brown obsessive compulsive scale;
• Having checking symptoms;
• Understanding and accepting the study;
• Giving his written informed consent to the study.

Exclusion Criteria:

• Claustrophobia;
• Cerebral abnormality;
• Chronic absenteism to CBT (more than 5 missed sessions during the whole therapy).

In case of exclusion of the study either decided by the patient himself or by the investigator, a debriefing is proposed by a psychologist.