Neuropsychiatric effects of subthalamic deep brain stimulation

The subthalamic nucleus (STN) is a subcortical, glutamatergic, excitatory, relay nucleus that increases the inhibitory drive of the basal ganglia and suppresses action. It is of central relevance to the neuropsychological construct of inhibition, as well as the pathophysiology of Parkinson's disease (PD). Deep brain stimulation (DBS) of the STN (STN-DBS) is an established surgical treatment for PD that can be complicated by adverse neuropsychiatric side effects, most commonly characterized by impulsivity and mood elevation, although depression, anxiety, apathy, and cognitive changes have also been reported. Notwithstanding these adverse neuropsychiatric effects in PD, STN-DBS may also have a role in the treatment of refractory psychiatric disorders, as more is understood about the physiology of this nucleus and techniques in neuromodulation are refined. In this chapter, we link neuropsychiatric symptoms after STN-DBS for PD to the biological effects of electrode implantation, neurostimulation, and adjustments to dopaminergic medication, in the setting of neurodegeneration affecting cortico-striatal connectivity. We then provide an overview of clinical trials that have employed STN-DBS to treat obsessive-compulsive disorder and discuss future directions for subthalamic neuromodulation in psychiatry.