Objective: Microelectrode recordings are the standard procedure for intraoperative, electrophysiological mapping of the STN[1]. We investigated a novel methodology to detect the STN sweet spot with information acquired via the macro-contacts of the finally implanted electrode leads. Recording local field potentials (LFPs) with directional electrode leads may furthermore provide additional topographic information.

Background: Current intraoperative techniques are particularly suited to determine the borders of the STN. Beta-band activity as a clinically relevant pathological biomarker of PD [2] may provide additional information with regard to the sweet spot for targeted DBS within the STN.

Method: The final electrode leads were advanced in 1mm steps across the STN region. At each millimeter, 30s of monopolar recordings were acquired. Beta peaks (13-32Hz) were identified online for each contact of the directional lead (Abbott Infinity, St. Jude Medical) in npatients=12 (nhemispheres=22) by calculating the power spectrum density. Within-patient STN sweet spots were determined by identifying macro-contacts with a beta-peak significantly different from the other contacts using t-tests (2-tailed). Beta-peaks along the implantation-vector were evaluated using a ranksum test. Applying a permutation-test (10.000 permutations) with a nested ranksum test (two-sided; p=0.05) confirmed overall peak detection.

Results: Online detection of STN sweet spots can be achieved by measuring statistically significant (p < 0.001) beta-power amplitude changes via the macro-contacts along the dorsoventral surgical trajectory. The exact level and direction of the macro-contacts with the highest beta power at target depth were identified (p < 0.05) for selection of clinically applied directional stimulation.

Conclusion: This novel approach allows to determine the final electrode position in <12min on the basis of individual pathophysiological information. The clinical effectiveness of this implantation method needs to be confirmed in future studies with clinical follow-up data.

References: [1] Hutchison WD, Allan RJ, Opitz H, Levy R, Dostrovsky JO, Lang AE, Lozano AM. Neurophysiological identification of the subthalamic nucleus in surgery for Parkinson’s disease. Annals of Neurology: Official Journal of the American Neurological Association and the Child Neurology Society. 1998 Oct;44(4):622-8. [2] Kühn AA, Tsui A, Aziz T, Ray N, Brücke C, Kupsch A, Schneider GH, Brown P. Pathological synchronisation in the subthalamic nucleus of patients with Parkinson’s disease relates to both bradykinesia and rigidity. Experimental neurology. 2009 Feb 1;215(2):380-7.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/online-determination-of-the-stn-sweet-spot-based-on-beta-power-measured-with-directional-macro-contacts-of-the-final-dbs-lead/