Neuronal correlates of obsessions in the caudate nucleus

Background: Metabolic overactivity of corticosubcortical loops including the caudate nucleus (CN) has been reported in obsessive-compulsive disorder (OCD) using functional imaging techniques. However, direct proof of a modification of neuronal activity within the CN of OCD patients is still lacking. We tested the hypothesis that obsessions or compulsions might be associated with particular features of neuronal activity in the CN of OCD patients. Methods: Single unit recordings were performed peroperatively in the CN of three patients with severe forms of obsessive-compulsive disorder (OCD) who were candidates for deep brain stimulation of the CN. Severity of obsessions was assessed preoperatively with the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) and peroperatively with a subjective obsession score based on a visual analog scale (VAS). Results: Frequency of CN discharge and variability of interspike intervals were found to be abnormally high in two patients with a high VAS score during surgery but not in one with a low VAS score. Lateralization and depth of recording influenced neuronal activity variably among patients. Conclusions: Because the three patients had high Y-BOCS scores before surgery, these findings suggest that cauclate hyperactivity in OCD is concomitant with the occurrence of the obsession process.