Cross-hemispheric effects of subthalamic nucleus deep-brain stimulation in Parkinson’s disease

Subthalamic nucleus (STN) deep brain stimulation (DBS) is an effective treatment for Parkinson's disease in patients who have developed complications of levodopa therapy. Suppression of beta oscillations in the STN is associated with improvement of rigidity and bradykinesia. Newer implantable pulse generators can detect local field potentials (LPF) in the STN, and stimulation modulation allows the suppression of beta oscillations with resulting symptomatic improvement. This effect is thought to occur at the actively adjusted STN; LPF suppression can be monitored during routine DBS programming in the clinic. In this exploratory, retrospective analysis, we performed spectral analysis of the effects of current increase in both the actively adjusted and unadjusted STN in 26 patients from two different cohorts. We found that an ipsilateral current increase resulted in concurrent power reduction both in the ipsilateral and contralateral STN in the low-beta (13-22.5Hz) and high beta (23-30.5Hz) ranges in 77% of patients. The relative level of bilateral power reduction was more pronounced in the low beta-range (35%) than in the high beta range (19%). In the gamma range (31-125Hz) 46% of patients showed a bilateral power reduction while 19% showed a bilateral power increase. These cross-hemispheric effects were not significantly associated with demographic, clinical or stimulation parameters, or GBA1 status. To determine whether this phenomenon has clinical significance and, potentially, to inform stimulation algorithms, new methodologies that allow for chronic concurrent monitoring of bilateral LFP suppression during unilateral stimulation adjustment need to be developed and assessed in longitudinal, prospective studies.