Objective: To relate the DBS evoked cortical potential (ECP) P25 to the suppression of tremor.

Background: DBS‑ECPs have been investigated in DBS of the subthalamic nucleus (STN) as possible biomarkers for the activation of different neuroanatomical pathways. Recently, we postulated that P25, a positive deflection observed 25ms after the stimulation pulse over the motor cortex, is most likely related to activation of cerebello-thalamo-cortical circuitry and might thus be related to tremor suppression.

Method: Using scalp EEG we recorded DBS‑ECP from all available DBS contacts in n=20 subjects with Parkinson’s disease (PD) and STN‑DBS and n=6 subjects with essential tremor (ET) and DBS of the posterior subthalamic area and the ventral intermediate nucleus (PSA/VIM). In total, this dataset included n>1100 DBS settings. We then used voxel‑wise DBS mapping to relate the occurrence of DBS-ECPs to their neuroanatomical origin. We then used a second dataset, which investigated DBS‑induced improvement in rest, postural, and intention tremor on each available contact in n=24 subjects with PD and STN‑DBS and n=16 subjects with ET and PSA/VIM‑DBS (n>790 DBS settings). Sampling stimulation maps from our DBS-ECP dataset at the DBS locations of our tremor dataset, we were able to generate synthetic P25 amplitudes and related these to the observed changes in tremor.

Results: P25 could be reliably identified in DBS-ECP data from both STN‑DBS and PSA/VIM‑DBS. P25 occurred when stimulating medial to the STN within the PSA and the ventral VIM. Synthetic P25 amplitudes generated for each DBS setting in our tremor dataset were able to predict improvements in postural and intention tremor with up to 23% of variance in tremor improvement being explained by P25 amplitude alone. An additional exploratory analysis of n = 3 hemispheres for postural tremor and n = 4 hemisphere for intention tremor for which both DBS‑ECP recordings and tremor assessments were available, also showed a direct correlation between P25 amplitudes and tremor improvement. Furthermore, the DBS contact with the highest P25 amplitude also had the highest improvement in postural tremor in 2 out of 3 hemispheres while 1 of the 2 contacts with the highest P25 amplitude had the highest improvement of intention tremor in 4 out of 4 hemispheres.

Conclusion: This study provides further evidence that P25 should be prospectively investigated as an electrophysiological biomarker for the suppression of tremor.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/dbs-evoked-cortical-potentials-can-predict-tremor-suppression/