Electrical stimulation of afferent pathways for the suppression of pathological tremor

Pathological tremors are involuntary oscillatory movements which cannot be fully\ua0attenuated using conventional treatments. For this reason, several studies have\ua0investigated the use of neuromuscular electrical stimulation for tremor suppression. In\ua0a recent study, however, we found that electrical stimulation below the motor threshold\ua0also suppressed tremor, indicating involvement of afferent pathways. In this study, we\ua0further explored this possibility by systematically investigating how tremor suppression\ua0by afferent stimulation depends on the stimulation settings. In this way, we aimed at identifying the optimal stimulation strategy, as well as to elucidate the underlying\ua0physiological mechanisms of tremor suppression. Stimulation strategies varying the\ua0stimulation intensity and pulse timing were tested in nine tremor patients using either\ua0intramuscular or surface stimulation. Significant tremor suppression was observed in six\ua0patients (tremor suppression > 75% was observed in three patients) and the average\ua0optimal suppression level observed across all subjects was 52%. The efficiency for\ua0each stimulation setting, however, varied substantially across patients and it was not possible to identify a single set of stimulation parameters that yielded positive results in all\ua0patients. For example, tremor suppression was achieved both with stimulation delivered\ua0in an out-of-phase pattern with respect to the tremor, and with random timing of the\ua0stimulation. Overall, these results indicate that low-current stimulation of afferent fibers\ua0is a promising approach for tremor suppression, but that further research is required to\ua0identify how the effect can be maximized in the individual patient