(42) Localizing Beta Oscillations in the Subthalamic Nucleus Using Directional DBS Recordings and Computational Modeling

Introduction: Local field potentials (LFPs) recorded from the subthalamic nucleus (STN) in the beta frequency range exhibit abnormally elevated power in Parkinson's disease (PD) patients. However, questions remain on the spatial location, volumetric size, and temporal stability of the beta synchrony in the STN. Therefore, we employed advanced biophysical models, coupled to experimental LFP recordings, to characterize the neural sources underlying beta synchrony in PD patients.

Methods: Intra-operative LFPs, recorded with a sampling rate of 1000 Hz, were acquired from directional DBS leads implanted in five PD patients. Patient-specific models, representing the DBS electrode in the neuroanatomy, as well as the STN neural activity, were used to simulate their LFP signals. A fitness function was employed to assess the similarity between the experimental and model LFP signals. The fitness function then guided our source localization process to determine the spatial characteristics of a beta synchronous volume in the STN that optimally fit each patient. We also used the model system to evaluate the stability of the beta synchronous volume over time, and compare different bipolar referencing schemes for use in clinical source localization strategies.

Results: Our patient-specific LFP models were able to uniquely localize beta oscillations across patients, with the synchronous neuron volume typically located in the dorsolateral region of the STN. A vertico-directional referencing scheme was found to be the most effective strategy for localizing beta oscillations in the STN. Source localization results from the patient-specific LFP models remained consistent even when reducing the sampling rate to 256 Hz.

Conclusion: Characterizing the spatial characteristics of beta oscillations within the STN allows for definition of a patient-specific target volume for DBS and identification of a contact for therapeutic stimulation.