Objective: The aim of this study was to investigate the electrophysiological characteristics of intra and extra STN LFPs in PD to better locate the source of these oscillations.

Background: Enhanced beta band oscillations and their entrainment of neuronal spiking are an electrophysiological hallmark of Parkinson’s disease (PD). Beta band synchronization is modulated by both dopamine medications and DBS in a manner that correlates with clinical outcome. Although STN spiking activity and LFP recordings suggest that STN beta activity is most prominent in the dorsolateral STN, the LFP characteristics beyond the assumed borders of the STN remain unknown.  

Methods: Eight PD patients were bilaterally implanted in 11 STNs with an 8 ring-contact DBS lead (Boston Scientific Corporation). Subcortical LFPs were recorded intra-operatively from each contact in the off medication-awake-rest-eyes open state. Each contact was localized relative to STN borders based on microelectrode recordings. The contact array covered ventral and dorsal STN, Zona Incerta (ZI) and lateral thalamus or white mater. Signals were sampled at 3 kHz, and referenced to the adjacent contact. Power spectral density was computed for each contact pair, averaged across multiple frequency bands (theta, delta, alpha, low beta, high beta and broadband gamma). Phase distributions of beta range band-pass filtered signals were computed for every contact pair.   

Results: Oscillatory activity in the beta band was found in all contact pairs covering the dorsal STN. In 8/11 STNs, beta peak was bi-phasic, having one peak at low and the other at high beta range. Similar beta power was also found in the ventral STN. The phase of the filtered beta signal seemed to exclusively reverse across contacts located in dorsal, but not ventral STN. The contact pairs covering ZI had significantly lower beta power. Very low beta power was found in contacts that cover white matter or thalamus. Other frequency bands were not altered significantly, in terms of power, across contact pairs.

Conclusions: We found the largest beta power and phase-reversal of beta signals to be localized to the dorsal STN. These findings support the dorsal STN as the primary source of beta oscillations in the subthalamic region, and argue against the hypothesis that STN beta activity represents volume-conducted cortical activity.   

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MDS Abstracts - https://www.mdsabstracts.org/abstract/eight-contact-lfp-recordings-in-the-subthalamic-region-localize-beta-source-to-the-dorsal-stn/