Selection of optimal programming contacts based on local field potential recordings from subthalamic nucleus in patients with Parkinson's disease.

Parkinson’s disease (PD) affects more than 500,000 people in the United States, with an annual incidence of 50,000 new cases per year.1 There is a sizable proportion of PD patients whose motor symptoms cannot be adequately controlled with medications. In these patients, deep brain stimulation (DBS) of the subthalamic nucleus (STN) has emerged as an effective neurosurgical treatment. DBS therapy involves implanting quadripolar electrodes into specific targets in the brain and connecting the electrodes to an implanted pulse generator (IPG). The procedure is generally done in 2 stages, the first involving DBS electrode implantation and, at a later stage, IPG implantation followed by IPG programming to deliver constant stimulation at a particular voltage, rate, and pulse width. DBS programming for each patient includes the selection of appropriate electrode contacts, voltage, and pulse width to maximize efficacy and minimize side effects of stimulation. The programming process requires time-consuming assessments by experienced personnel of efficacy and side effects at each of 4 brain electrode contacts, individually and in various combinations. Improperly programmed DBS devices can be a source of inadequate symptom control.2 Information that could identify in advance the optimal contacts for stimulation would expedite and increase the accuracy of the programming process. The 4 electrode contacts, numbered 0 to 3 from most caudal to most rostral, are 1.5 mm in length, spaced 0.5 mm apart, and span a total distance of 7.5 mm (Medtronic model 3389; Medtronic Corp., Minneapolis, Minnesota). As the rostrocaudal extent of the STN is 4 to 5 mm, typically no more than 2 DBS electrode contacts are located within the STN. In addition to delivering stimulation, DBS electrodes can also be used to record local field potentials (LFPs). LFPs are thought to represent aggregate activity from populations of neurons, synapses, axons, and glia surrounding the electrode tip. LFP recordings have been used to glean information about neural rhythms involving the STN and surrounding structures.3 Recent data suggest that LFPs recorded from the STN can provide important clues about target localization4,5 and disease state in patients. Normal voluntary movements appear to be preceded by a decrease in the amplitude of β-band LFP oscillations and an increase in γ-band activity in the STN and other elements of the basal ganglia–thalamocortical circuitry.6 A pathological increase in the antikinetic β-band activity, as well as a decrease in the prokinetic γ-band activity, is thought to accompany parkinsonism.7 Most studies of LFP activity recorded from the STN of PD patients have been conducted in the immediate postoperative period. In this study, we chose to record LFP activity 3 weeks after electrode implantation, when the potentially confounding effect on neuronal activity posed by the focal cerebral edema induced by surgery can be expected to have abated. Thus, 48 hours of LFP recordings were obtained at the time when patients with implanted DBS electrodes returned to the hospital for surgery to connect their previously implanted DBS electrodes to the IPG. Our goal was to test the hypothesis that LFP data recorded from DBS electrodes could be used to identify the optimal contact(s) for postoperative DBS programming. To this end, patients underwent postoperative DBS programming, and results were then compared with LFP data collected from each contact to check for correlations. In addition, we compared the results of the postoperative LFP recordings with LFP recordings made during the DBS electrode implantation procedure to examine the utility of intra-operative LFP recordings in guiding electrode contact selection for IPG programming.