Master of Science
Garland, S. Jayne
Sensory electrical stimulation can be used to suppress tremor in Parkinson’s disease. This study investigated the central mechanism underlying this suppression in healthy participants. Reciprocal inhibition (RI) of the wrist flexors before and after a session of sensory electrical stimulation (SES) applied to the antagonistic extensor muscles was assessed using electromyography. It was hypothesized that a 15-minute session of SES, rated by participants as a 3 on a 0-10 pain scale, would produce an increase in RI. Seven of the 18 participants experienced an increase in RI at 0-5 minutes post stimulation, which returned to baseline at 10-15 minutes. The findings of the present experiment suggest that increases in RI are only observed in a “responders” subgroup consisting of predominantly male participants. More research is needed to understand the optimal stimulation intensity and any sex-linked factors that are important to produce reliable changes in reciprocal inhibition following sensory electrical stimulation.
Summary for Lay Audience
Tremor is an involuntary rhythmic movement that is commonly found in the forearm of people with Parkinson’s disease. These rhythmic movements at the joint are generated by contractions of the two opposing sets of muscles called “extensors” and “flexors”, creating a back-and-forth motion. One approach to reduce tremor is to apply weak electrical stimulation to the muscle in a pattern to oppose the movement. It has been thought that inhibition in the spinal cord may play an important role in this process. By electrically stimulating the extensor muscles with weak electrical current that does not produce muscle contraction i.e. sensory electrical stimulation, it is possible to reduce the contraction of the flexor muscles. To test this mechanism in the wrist muscles, the level of inhibition present in the wrist flexors was measured before and after a sensory electrical stimulation was applied to the wrist extensors. The electrical stimulation was mild causing slight discomfort (3 on a 0-10 pain scale, with 0 for no pain and 10 being the worst pain imaginable) to the participants. It was expected that after a15-minute session of this stimulation the inhibition to the flexors would increase. Although there was a significant inhibition present in the flexors for all participants, the expected increase in inhibition after the sensory electrical stimulation of the extensors was found only in a subgroup of primarily male participants. A possible explanation is that the intensity of the sensory electrical stimulation was not strong enough for some participants to produce the expected changes in inhibition. More research is needed to understand the best stimulation intensity and any sex-linked factors that influence the inhibition following sensory electrical stimulation.
Box, Devin K., "Spinal Excitability Changes Following Sensory Electrical Stimulation of The Forearm" (2021). Electronic Thesis and Dissertation Repository. 7836.