Impulsivity, impulse control disorders, and subthalamic stimulation in Parkinson’s disease

Subthalamic nucleus (STN) stimulation in advanced Parkinson’s disease is a very powerful treatment for a highly selected group of patients. However, behavioral problems after neurosurgery have frequently been reported and may hamper the therapeutic success. In particular, impulsivity and impulse control disorders are often discussed as adverse effects of STN stimulation, and there is an ongoing debate whether stimulation causes or improves behavioral problems. We here point out that behavior after surgery for STN stimulation depends on five interacting factors: (1) impulsivity as an effect of STN stimulation, (2) hypo- and hyperdopaminergic behaviors as a result of changes of dopaminergic medication, (3) individually different mesolimbic denervation, (4) exact location of the electrode within the STN, and (5) reactive psychosocial changes. The complex interplay of these factors has so far not been taken into account appropriately to understand the postoperative behavioral events. We here propose a two axes model that may help clinicians understand the effects of treatment changes after neurosurgery and provide a basis for optimization of stimulation parameter programming and adjustment of dopaminergic medication.