Changes of oscillatory activity in the subthalamic nucleus during obsessive-compulsive disorder symptoms: two case reports.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has positive and negative effects on mood and cognition, as shown in patients suffering from Parkinson's disease (PD) and severe obsessive-compulsive disorders (OCD). Such behavioural and clinical effects suggest that the STN has an important function in limbic circuitry, which still needs to be clarified from electrophysiological recordings. Here we report two exceptional cases of OCD patients in whom local field potentials (LFP) of the anterior STN were directly recorded during acute obsessive-compulsive symptoms. We found significant symptom-related changes in different frequency bands, with no clear preferential oscillatory pattern. The overall modified STN activity during OCD symptoms suggests a mixture of both pathological and compensatory mechanisms that would reflect the maintenance of an over stable motor/cognitive/emotional set. Whether this activity propagates throughout the entire cognitive-limbic loops that are impaired in OCD is an interesting question for future research in larger series of patients.