Surgical modulation of behaviors and affects by deep brain stimulation

Deep brain stimulation (DBS) has been proposed for 25 years to modulate motor cortico-basal neural networks to treat movements disorders. Functional neuroimaging studies have showed that some psychiatric disorders as Tourette’s syndrome (TS), obsessive compulsive disorders (OCD) and major depression (MD) probably result from the dysfunction of similar neural networks. Neuromodulation of these networks using DBS has been shown to successfully improve patients suffering from severe and refractory forms of these diseases, in several pilot and/or comparative studies. Several brain structures, belonging to these networks, have been proposed as potential efficient DBS targets. Several prospective open studies have shown that 50-60 % of the patients suffering from MD respond (depression score decrease >50%) to DBS targeting the subgenual portion of the cingulum (Cg25) or the nucleus accumbens (NAcc). In OCD several DBS targets have been proposed, including the NAcc, the subthalamic nucleus (STN), the anterior limb of the internal capsule, and the ventral striatum. Efficacy of STN-DBS and NAcc-DBS has been confirmed in comparative blinded studies. In TS, tics may be dramatically improved by DBS of the thalamus (centro-median and parafascicular nuclei) or the limbic part of the globus pallidus internus (GPi).These results are encouraging but need to be confirmed in large comparative studies before to discuss the place of surgery in the management of these affections. The mechanisms of action and the predictive factors of DBS efficacy have not been identified yet. The ethical aspects of this approach have to be discussed too.