Frequency-selective suppression of essential tremor via transcutaneous spinal cord electrical stimulation

Background. Essential tremor is a common and debilitating condition, yet current treatments often fail to provide satisfactory relief. Transcutaneous spinal cord electrical stimulation has emerged as a potential non-invasive neuromodulation technique capable of disrupting the oscillatory activity underlying tremors. Objectives. This study aimed to investigate the potential of transcutaneous spinal cord electrical stimulation to suppress essential tremor in a frequency-dependent manner.Methods. Eighteen essential tremor patients completed the study. The experiment consisted of 60 s postural tremor recording, during 5 conditions: no stimulation, transcutaneous spinal cord electrical stimulation at tremor frequency, transcutaneous spinal cord electrical stimulation at 1 Hz, transcutaneous spinal cord electrical stimulation at 21 Hz and trapezius stimulation (serving as a control). Tremor frequency and amplitude were analysed and compared across the conditions. Results. We found tremor amplitude reduction at tremor frequency stimulation, during the entire trial but significant only during the second half of the stimulation. This result was reinforced by the observation that the same stimulation resulted in the highest number of responders. Transcutaneous spinal cord electrical stimulation at 1 Hz showed a trend toward decreased tremor amplitude in the latter half of stimulation, though this trend did not reach statistical significance. Stimulation at 21 Hz did not produce any significant alterations in tremor, while trapezius stimulation exacerbated it. Notably, during tremor frequency stimulation, a subgroup of responders exhibited consistent synchronization between tremor phase and delivered stimulation, indicating tremor entrainment.Conclusions. Cervical transcutaneous spinal cord electrical stimulation holds promise for alleviating postural tremor in essential tremor patients when delivered at the subject’s tremor frequency. The observed changes in tremor amplitude likely result from the modulation of spinal cord circuits by transcutaneous spinal cord electrical stimulation, which disrupts the oscillatory drive to muscles by affecting afferent pathways or spinal reflexes. However, the possibility of an interplay between spinal and supraspinal centres cannot be discounted.