Spatial extent of β oscillatory activity in and between the subthalamic nucleus and substantia nigra pars reticulata of Parkinson's disease patients.

Parkinson's disease (PD) is accompanied by a significant amount of β-band (11 Hz-30 Hz) neuronal and local field potential (LFP) oscillatory activity in the subthalamic nucleus (STN). Previous studies have shown significant coherence between neuronal firing and LFPs at β frequencies at sites separated by ~1 mm and that the magnitude of β oscillatory LFP activity and coherence are greatly reduced following levodopa administration. However, these data have been collected from large DBS contact electrodes or pairs of microelectrodes in proximity to each other and so it is not clear whether all regions of STN are synchronized. It is also not known whether the LFP and neuronal activity in the substantia nigra pars reticulata (SNr) shows β activity and whether it is coherent with STN activity. Therefore, the aim of this study was to measure the spatial extent of β coherent activity in the STN and coherence between STN and SNr in PD patients OFF levodopa by systematically varying the distance between the dual microelectrodes. A total of 170 pairs of recordings were collected from 20 patients at rest undergoing DBS-STN implantation surgery. Trajectories passed dorsoventrally through STN and into SNr using two microelectrodes initially ~1mm apart. Once the microelectrodes entered the dorsal STN, one of the two was held stationary, while the other one was advanced into SNr over a distance of ~4-6mm. Pairs of recordings were obtained from STN/STN (n=111), STN/SNr (n=42), and SNr/SNr (n=17). We confirmed previous reports of a progressive attenuation in β power as electrodes were driven from dorsal to ventral STN and into SNr. Furthermore, we found significant β-LFP coherence across the dorsoventral extent of STN. Detailed analysis suggested that at least some of the ventral STN and SNr beta activity was locally generated rather than arising from volume conduction from dorsal STN and thus suggests that β oscillations synchronize both the input and output nuclei of the basal ganglia.
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