Introduction: Despite the clinical efficacy of thalamic deep brain stimulation (DBS) for essential tremor (ET), little is known about how therapeutic DBS alters neural activity to disrupt pathological tremor. Prior studies have investigated motor cortical activity during DBS and suggest that therapeutic DBS activates cortex at the stimulation frequency or its subharmonics and significantly reduces alpha band activity (8-13 Hz), but these findings have not been confirmed in chronically implanted patients. Neural biomarkers of effective DBS may elucidate ET mechanisms and provide an alternative method by which DBS can be programmed.

Methods: We recruited two ET patients chronically implanted with VIM DBS and ECoG strip over the arm area of motor cortex. We tested a range of bipolar stimulation contacts and amplitudes at nominal frequency and pulsewidth while evaluating tremor and recording local field potentials (LFPs) from motor cortex. A smartwatch with inertial measurement unit (IMU) was used to quantify tremor and distinguish between effective (greater than 90% of tremor reduction) and ineffective DBS settings.

Results: We compared the LFP signal power in theta (4-8 Hz), alpha (8-13 Hz), beta (13-30 Hz), and subharmonic (70 Hz) bands for effective, ineffective and off DBS settings. We found that effective DBS significantly decreased motor cortical theta, alpha, and beta power relative to ineffective DBS (p < 0.01, p < 0.01, p < 0.001, respectively) and off DBS (p < 0.01, p < 0.001, p < 0.001, respectively), and that effective DBS significantly increased subharmonic power relative to ineffective DBS (p < 0.01) and off DBS (p < 0.01).

Conclusions: These findings in chronically implanted patients support previous studies that used EEG and ECoG during surgery to characterize motor cortical activity during DBS. Future studies will test additional patients and investigate whether these neural biomarkers may be used to guide DBS programming sessions.

Patient Care: This research has the potential to improve how DBS is delivered.

Learning Objectives: By the conclusion of this session, participants should be able to identify putative cortical biomarkers of effective DBS to treat essential tremor

References: 1. Air E, Ryapolova-Webb E, de Hemptinne C, Ostrem J, Galifianakis N, Larson P, Chang E, Starr P. Acute effects of thalamic deep brain stimulation and thalamotomy on sensorimotor cortex local field potentials in essential tremor. Clinical Neurophysiology. 2012;123(11):2232-2238. 2. Walker H, Huang H, Gonzalez C, Bryant J, Killen J, Knowlton R, Montgomery E, Cutter G, Yildirim A, Guthrie B, Watts R. Short latency activation of cortex by clinically effective thalamic brain stimulation for tremor. Movement Disorders. 2012;27(11):1404-1412.