Improving Wrist Tremor Suppression via Targeted Application of Afferent and Interferential Stimulation Techniques

Upper limb tremors from Parkinson's Disease (PD) and Essential Tremor (ET) disease affect an estimated 6% of the global population. Patients face difficulties performing activities of daily living, leading to a reduced quality of life. Though treatments such as medication and deep brain stimulation exist, their limited applicability and potential risk leaves a large patient subset untreated. In contrast, non-invasive peripheral electrical stimulation (ES) therapies can be tailored to the user to optimally mitigate the symptoms of tremor. Fatigue-inducing functional electrical stimulation (FES) protocols have the highest efficacy of ES methods, with suppression ratios in the 50%s. In this work, we aimed to suppress tremors at the same level using sensory electrical stimulation (SES), which currently has efficacy levels in the 30-45 percent range. In addition to specially targeting the forearm pronator and supinator for stimulation, we introduce the use of deep interferential current (DIC) as a method to suppress postural wrist tremors in PD and ET populations. 1 ET and 1 PD subject completed a cup lift-and-hold task to elicit tremor as we applied and evaluated SES and DIC techniques. We found significant variability in performance between our PD and ET subjects, with the highest suppression ($>60 \%$) observed during SES for the PD subject. However, suppression was observed in all subjects for both SES and DIC, demonstrating the viability of our DIC approach while indicating the need for significant protocol optimization and individualization.