The Synergistic Effects of AIH and FES in Persons With MS

NMES: NMES refers to the application of mild electrical stimulation and is often used as an assistive technology for foot drop in MS and other neurologic conditions. The NMES-induced improvement in motor performance appears to be mediated primarily by an increase in corticomotoneuronal excitability. A single session of NMES applied over a peripheral nerve, has been shown to transiently increase net corticospinal excitability (increased MEP amplitude) in both able-bodied individuals and in people with neurological conditions. AIH: AIH involves breathing brief bouts of low levels of oxygen. Research has found AIH to be a safe and effective intervention resulting in increased ankle strength in people with MS. While AIH has shown potential in enhancing neuroplasticity in people with spinal cord injury (SCI), it has yet to be studied extensively in MS. Preliminary research in the MS population demonstrates that a single session of AIH enhances motor output, increasing voluntary muscle strength by as much as 15-20% within 60 minutes. Over the past decade, studies have found AIH can rapidly enhance neural plasticity in persons with incomplete SCI. AIH activates the serotonergic pathway, leading to increased activity of serotonin receptors and the synthesis of plasticity-related proteins. This plasticity is manifested by a rapid increase in voluntary muscle strength, emerging within 60-90 minutes. In this study, the investigators will examine how NMES, which has been shown to affect cortical excitability, and AIH, which has been shown to affect corticospinal plasticity, may synergistically enhance corticospinal excitability in people with relapsing form of MS. Foot drop is a common symptom in the diagnosis of MS where the inability to maintain active dorsiflexion during the swing phase of the gait cycle affects walking efficiency, instability, and falls. Seminal studies show that individuals with MS retain the ability to express plasticity even at higher levels of disease burden. This indicates that strategies targeting neuroplasticity can be used to enhance functional recovery and limit the impact of MS disability. The investigators will conduct a randomized, blinded, placebo-controlled, cross-over study in 20 MS patients with established motor deficits and controlled relapse activity and 20 control subjects with no neurological diagnosis.