Surgical treatment of Parkinson disease: past, present, and future.

Advances in functional neurosurgery have expanded the treatment of Parkinson disease (PD) to targeted electrical stimulation of specific nodes in the basal ganglia circuitry. Deep brain stimulation (DBS), applied to selected patients and difficult-to-manage motor fluctuations, yields substantial reductions in off time and dyskinesia. Emerging concepts in DBS include examination of new targets, such as the potential efficacy of pedunculopontine nucleus stimulation for treatment of freezing and falls, the use of pathologic oscillations in the beta band to construct an adaptive "closed-loop" DBS, and new technologies, including segmented electrodes to steer current toward specific neural populations.