Spinal reflex conditioning system for enhancing motor function recovery after incomplete spinal cord injury

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Project Summary People with spasticity due to chronic Spinal Cord Injury (SCI) can benefit from reflex operant conditioning therapy, as described in the parent application. Transcutaneous stimulation of the tibial nerve, an essential element of the soleus H-reflex conditioning we are implementing, can produce discomfort that varies from person to person. This discomfort is minimal and tolerable in most individuals who experience it. In up to 20% individuals, however, the discomfort from stimulation is not easily tolerable. As a result, the stimulation procedure cannot be administered and the individual may opt out of reflex conditioning therapy. For example, individuals with chronic pain due to SCI or individuals with hypersensitivity to transcutaneous stimulation can be more prone to experience discomfort from skin-surface stimulation. The exclusion of these individuals from the potential patient population is not ideal, but has been tolerated to date, because stimulation discomfort is a longstanding issue not unique to our procedures, and because the majority of candidate patients do elect to undergo operant conditioning therapy and experience its benefits. We recently made the unexpected discovery that surface stimulation with appropriately tuned multi-electrode configurations can reduce patient discomfort. By incorporating customizable control of multi-electrode stimulus configuration into our reflex conditioning system we propose to reduce the incidence of stimulation discomfort. This reduction of stimulation discomfort would expand the candidate patient base for the reflex operant conditioning therapy we are translating into clinical use, so that many more patients might benefit from it. In order to improve patient comfort during stimulation, while maintaining the same effectiveness in H-reflex elicitation as the standard single electrode stimulation, we propose three aims. Aim 1 will evaluate and finalize a stimulating electrode array design optimized for stimulation comfort, usability, and effectiveness. We will accomplish this aim by gathering feedback from serial trials on volunteers with various leg dimensions, using three different electrode design iterations. Aim 2 will examine the effectiveness, perception, and comfort level of different stimulation electrode configurations in volunteers with no neurological conditions. This aim will narrow the parameter space of potential electrode configurations which maximize recruitment and minimize discomfort. Aim 3 will test these optimal configurations on patients with neurological conditions. This aim will confirm whether at least one of the multi-electrode configurations will produce less discomfort than the conventional single-electrode stimulation. This aim will also confirm whether there is an increased probability that individuals who experience stimulation discomfort would elect to undergo extended operant conditioning therapy. The proposed administrative supplement will allow us to take advantage of the unanticipated opportunity to increase patient comfort involved with the reflex conditioning therapy that we are translating to the clinic. This advance should enhance clinical dissemination and adoption of the new system and expand the patient population that can benefit from it. These benefits should greatly increase the ultimate practical value of the project and are consistent with its peer- reviewed objectives.