Sensory electrical stimulation for suppression of postural tremor in patients with essential tremor

Abstract

Abstract. Essential tremor is an involuntary trembling of body limbs in people without tremor-related disease. In previous study, suppression of tremor by sensory electrical stimulation was confirmed on the index finger. This study investigates the effect of sensory stimulation on multiple segments and joints of the upper limb. It denotes the observation regarding the effect's continuity after halting the stimulation. 18 patients with essential tremor (8 men and 10 women) participated in this study. The task, "arms stretched forward", was performed and sensory electrical stimulation was applied on four muscles of the upper limb (Flexor Carpi Radialis, Extensor Carpi Radialis, Biceps Brachii, and Triceps Brachii) for 15 seconds. Three 3-D gyro sensors were used to measure the angular velocities of segments (finger, hand, and forearm) and joints (metacarpophalangeal and wrist joints) for three phases of pre-stimulation (Pre), during-stimulation (On), and 5 minute poststimulation (P5). Three characteristic variables of root-mean-squared angular velocity, peak power, and peak power frequency were derived from the vector sum of the sensor signals. At On phase, RMS velocity was reduced from Pre in all segments and joints while peak power was reduced from Pre in all segments and joints except for forearm segment. Sensory stimulation showed no effect on peak power frequency. All variables at P5 were similar to those at On at all segments and joints. The decrease of peak power of the index finger was noted by 90% during stimulation from that of On phase, which was maintained even after 5 min. The results indicate that sensory stimulation may be an effective clinical method to treat the essential tremor.

Electrical Stimulation of Afferent Pathways for the Suppression of Pathological Tremor

“…It is well-established that thalamic deep brain stimulation (Kalia et al, 2013) as well as stimulation of the dorsal column of the spinal cord (Fuentes et al, 2009) can desynchronize the neural activity causing several PD symptoms including tremor. Continuous surface stimulation of muscles at levels below motor threshold is also effective for tremor suppression, and may even last for several minutes after stimulation has been stopped (Heo et al, 2015). It can be hypothesized that our randomly timed stimulation may have evoked similar tremor suppression pathways as in Heo et al (2015), although it is likely that such pathways are better stimulated with continuous rather than random stimulation.…”

“…Continuous surface stimulation of muscles at levels below motor threshold is also effective for tremor suppression, and may even last for several minutes after stimulation has been stopped (Heo et al, 2015). It can be hypothesized that our randomly timed stimulation may have evoked similar tremor suppression pathways as in Heo et al (2015), although it is likely that such pathways are better stimulated with continuous rather than random stimulation. The effectiveness of appropriately-timed stimulation in our study demonstrates that Ia inhibitory pathways can be recruited for the purpose of tremor suppression.…”

“…Although our randomly-timed stimulation condition can be viewed as a kind of sham, to control for the effects of stimulation in general, the fact that sensory stimulation may influence tremor (e.g., Heo et al, 2015) underscores the need for a new kind of sham/placebo condition in future mechanistic studies. Because sensory stimulation is perceivable by patients, it is possible that unintended effects of anxiety, surprise, distraction, etc.…”

“…Furthermore, we hypothesized that differences in tremor suppression across stimulation settings could help to identify the physiological pathways through which tremor suppression occurred. For example, if the suppression is primarily achieved via cutaneous sensory afferents, which is a distinct possibility (Heo et al, 2015), then surface stimulation should produce superior results to intramuscular stimulation, and stimulation timing would be largely irrelevant. On the other hand, if activation of proprioceptive afferents (working via reciprocal inhibition pathways) is most important, then the appropriate timing of stimulation could be critical, and intramuscular stimulation would likely be the more comfortable, less distracting delivery method.…”

Mechanical vibration does not systematically reduce the tremor in Essential Tremor patients

“…Non-invasive wearable devices that stimulate or exert forces on the affected limb are an appealing alternative 23,24 . Examples of these devices span robotic exoskeletons 25,26 , functional electrical stimulation systems 27 , or devices that aim at recruiting afferent pathways [28][29][30] . Although many of them showed clear improvements during standard clinical tasks in convenience samples of patients, none of them -to the best of our knowledgehas gone beyond laboratory trials.…”