Detection of the subthalamic nucleus in microelectrographic recordings in Parkinson disease using the high-frequency (> 500 Hz) neuronal background

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✓Accurate and fast localization of the subthalamic nucleus (STN) during intraoperative electrophysiological monitoring can improve the outcome of deep brain stimulation surgery. The authors show a simple method of detecting the STN that is based on an analysis of the high-frequency (> 500 Hz) background (HFB) activity of neurons. The HFB reflects multiunit spiking activity close to the recording electrode, and its characteristic profile, which is higher in the STN than in neighboring structures, and facilitates delineation of both the dorsal and ventral STN borders.

Abbreviations used in this paper:ANOVA = analysis of variance; DBS = deep brain stimulation; HFB = high-frequency background; MER = microelectrode recording; MPTP = 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; MR = magnetic resonance; SN = substantia nigra; STN = subthalamic nucleus.

Article Information

Address reprint requests to: Peter Novak, M.D., Ph.D., Department of Neurology, Boston Medical Center, 715 Albany Street, D315, Boston, Massachusetts 02118. email:

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    Schematic demonstrating the processing of neuronal data. Small arrows show the flow of processing. Microelectrode recording traces (A) were obtained from the anterior thalamus (depth 4 mm), STN (depth 11.5 mm), and SN (depth 16.1 mm). Only a 0.25-second portion of the recordings is represented. Neuronal background traces (B) were obtained by removing large spikes from raw neuronal activity (A). High-frequency neuronal background was analyzed in the frequency domain by calculating spectral power densities (C) from the neuronal background. Each line in C represents a power spectral density at high frequencies (range 500–2000 Hz) calculated from a 10-second segment obtained at different electrode depths. The HFB that corresponds to a spectral power within the 500- to 2000-Hz range is elevated in the STN, with sharp changes in the spectral density at the dorsal and ventral borders, which are designated by large arrowheads.

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    Graph revealing a representative profile of HFB activity as a function of electrode depth. Each circle represents a mean HFB power ( article image

    HFB) obtained from a 10-second recording. Arrows indicate the STN borders. The dorsal border depth was 9.4 mm; the ventral border depth, 14.5 mm. The borders obtained using the HFB method were identical to those obtained during intraoperative electrophysiological monitoring. H2 = H2 field of Forel.

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    Graph depicting the average HFB activity (solid line) and 95% confidence intervals (dotted lines) obtained from 30 neuronal intraoperative recordings. The mean HFB powers obtained from each patient were aligned at the dorsal STN border (arrow, depth 0 mm) and then averaged. The electrode trajectory starts on the left.

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    Graph featuring examples of optimal and suboptimal tracks visualized by HFB activity. There is no elevation in the HFB activity within the depth of the STN on the first track, which missed the STN. Neuronal activity obtained from the second track, placed 2 mm medially with respect to the first track, has increased the HFB activity within the STN. There is also a quiet zone associated with a transient decrease in the HFB within the STN at a depth of 15 mm. In this patient, the dorsal border was assigned at an identical depth during both intraoperative electrophysiological monitoring and HFB analysis (9.17 mm). During electrophysiological monitoring, ventral border assessment was ambiguous, because there was a decrease in neuronal activity including both the spiking and neuronal background at a depth of 15 mm. Both spiking and neuronal background activity increased with further advancing of the electrode until a sustained decrease in neuronal activity was observed. According to the HFB criteria, the ventral border depth was at 16.6 mm. Each circle represents a mean HFB power ( article image

    HFB) obtained from a 10-second recording.

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    Bar graph demonstrating the mean values and respective standard deviations of the high-frequency neuronal background activity obtained from the thalamus/zona incerta, STN, and SN.



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