Abstract
Parkinson's disease and essential tremor are common movement disorders characterized by distinct motor symptoms. Deep brain stimulation targeting the subthalamic nucleus has shown efficacy in managing Parkinson's disease symptoms, whereas the posterior subthalamic area is an emerging target for essential tremor. This analytical cross-sectional study investigates the electrophysiological activity of the subthalamic nucleus in Parkinson's disease and essential tremor patients from deep brain stimulation surgeries to understand the underlying neural oscillatory mechanisms. Microelectrode recordings during deep brain stimulation surgery from 35 Parkinson's disease patients targeting the subthalamic nucleus and 21 essential tremor patients simultaneously targeting the posterior subthalamic area and subthalamic nucleus using a novel dual electrode technique were analysed for the main analysis. Additionally, subthalamic nucleus data from a subgroup of 12 Parkinson's disease patients was compared with seven essential tremor patients who were matched based on the y-coordinate of the electrode. A final comparison was made between a third subgroup of nine Parkinson's disease patients with satisfactory subthalamic nucleus recordings in the posterior BenGun location and 21 essential tremor patients. Recordings were collected from two medical centres with a common electrophysiology team. Root mean square and spectral analysis were employed as well as statistical analysis of demographic and recorded subthalamic nucleus anatomical dimensions. Relative dimensions of subthalamic nucleus physiological regions did not differ between the main groups. The motor subregion of the subthalamic nucleus in Parkinson's disease patients exhibited significantly increased beta frequency power (13-30 Hz). Conversely, essential tremor patients did not show this increase, suggesting distinct pathophysiological mechanisms. Additionally, the subthalamic nucleus spiking activity, as measured by RMS analysis, was higher in Parkinson's disease patients. y-coordinate matched, and posterior subthalamic nucleus Parkinson's disease patient comparisons confirmed the higher beta frequency power in Parkinson's disease patients only. These findings underscore the different neural dynamics between Parkinson's disease and essential tremor. They highlight the role of beta oscillations in Parkinson's disease's motor symptoms and raise questions about the absence of beta oscillations in essential tremor, whether it reflects a normal lack of beta activity or an active suppression of a normal beta stop signal.