Mechanism(s) of deep brain stimulation and insights into cognitive outcomes in Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor, cognitive, neuropsychiatric, autonomic, and other nonmotor symptoms. Deep brain stimulation (DBS) at high frequency is now considered the most effective neurosurgical therapy for movement disorders, especially PD. An electrode is chronically implanted in a particular area of the brain and, when continuously stimulated, it significantly alleviates motor symptoms. In Parkinson's disease, the common target nuclei of high frequency stimulation (HFS) are the basal ganglia nuclei, such as the internal segment of the pallidum and the subthalamic nucleus (STN), with a preference for the STN in recent years. Two fundamental mechanisms have been proposed to underlie the beneficial effects of HFS: either silencing or excitation of STN neurons. This article highlights the recent views concerned with the mechanisms of DBS. Although the efficacy of DBS for the motor symptoms of advanced PD is well established, the effects of DBS on the cognitive and neuropsychiatric symptoms are less clear. The cognitive aspects of DBS for PD have recently been of considerable clinical and pathophysiological interest. This article also reviews the published literature on the cognitive aspects of DBS for PD.