Objective: To examine the effects of microelectrode penetration into the STN on local field potential recordings in patients with PD undergoing bilateral STN DBS implantation.

Background: DBS of the STN is an effective treatment for both controlling symptoms and improving quality of life in PD [1]. Characterization of electrophysiological recordings during DBS surgery is critical for anatomical targeting and is extensively utilized to investigate physiologic markers of PD [2,3]. Transient improvement in clinical symptoms has been reported after microelectrode penetration, but the mechanism(s) underlying this improvement are not well understood [4]. Therefore, we sought to determine the effects of a microlesion, caused by penetration of a microelectrode, on STN electrophysiological activity.

Method: We obtained intraoperative microelectrode recordings from four patients diagnosed with PD during bilateral implantation of DBS electrodes in the STN. The electrode tip obtained 8-second recordings at 0.3mm steps between the dorsal border of the STN, as determined by electrophysiological criteria [5,6], until the ventral border was reached (Figure 1). The microelectrode was then extracted using 0.3mm-step increments to ensure repeat 8s resting recordings were obtained from the same anatomic positions. As a measure of electrophysiological activity, we calculated the power in different high frequency bands (low gamma [30-70Hz], high gamma [70-200Hz], and high frequency activity [HFA; 200-400Hz]). To examine changes across patients, we normalized the data as the percent change in average power at similar depths between microelectrode insertion and extraction and analyzed it using one sample Wilcoxon nonparametric tests.

Results: We found a significant decrease in power in all high frequency bands as a result of microelectrode penetration (p<0.0001 each). The largest percent change in power came from the upper HFA band (300-400Hz), which showed a 44% decrease from insertion to extraction of the microelectrode. The low gamma, high gamma, and lower HFA (200-300Hz) bands resulted in 13%, 30%, and 41% decreases, respectively.

Conclusion: Microelectrode penetration of the STN during DBS surgery causes a significant decrease in power in higher frequency bands. Transient improvements in the motor symptoms of PD due to a DBS microlesion may result from decreased spontaneous high frequency activity in the STN.

References: [1] Lozano AM, Lipsman N, Bergman H, Brown P, Chabardes S, Chang JW, et al. Deep brain stimulation: current challenges and future directions. Nat Rev Neurol. 2019;15(3):148-60. [2] Benazzouz A, Breit S, Koudsie A, Pollak P, Krack P, Benabid AL. Intraoperative microrecordings of the subthalamic nucleus in Parkinson’s disease. Mov Disord. 2002;17 Suppl 3:S145-9. [3] Amirnovin R, Williams ZM, Cosgrove GR, Eskandar EN. Experience with microelectrode guided subthalamic nucleus deep brain stimulation. Neurosurgery. 2006;58(1 Suppl):ONS96-102; discussion ONS96-. [4] Mann JM, Foote KD, Garvan CW, Fernandez HH, Jacobson CEt, Rodriguez RL, et al. Brain penetration effects of microelectrodes and DBS leads in STN or GPi. J Neurol Neurosurg Psychiatry. 2009;80(7):794-7. [5] Wang J, Hirschmann J, Elben S, Hartmann CJ, Vesper J, Wojtecki L, et al. High-frequency oscillations in Parkinson’s disease: spatial distribution and clinical relevance. Mov Disord. 2014;29(10):1265-72. [6] Yang AI, Vanegas N, Lungu C, Zaghloul KA. Beta-coupled high-frequency activity and beta-locked neuronal spiking in the subthalamic nucleus of Parkinson’s disease. J Neurosci. 2014;34(38):12816-27.

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