Neuromuscular dysfunction: characterization and rehabilitation
Date
2013
Authors
Paxton, Roger John, author
Tracy, Brian L., advisor
Malcolm, Matthew P., advisor
Reiser, Raoul F., II, committee member
Davies, Patricia L., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Manifestation of action in the physical world is reliant on afferent signaling, processing, efferent signaling, and transduction of this signal into force production and control at the musculature. A variety of neural conditions compromise this chain between signal input and control of force and movement. The overall objective of the four investigations discussed herein is the enhanced characterization and treatment of three conditions leading to neuromuscular dysfunction: healthy aging, peripheral neuropathy, and stroke. The population of the United States is "graying". Among the array of health issues associated with aging, decline of muscle force production and control is of key import. Little information exists for the relationship of neuromuscular control about the ankle to postural control in the context of aging. Experiment #1 investigated the contribution of neuromuscular control about the ankle to postural steadiness in healthy subjects who were young, old, and very old. The most robust correlations between ankle force control, postural stability, and physical function were found in the very old subjects. Peripheral neuropathy (PN) is a progressive condition in which neurons found beyond the central nervous system "die back". An increase in peripheral neuropathy incidence is virtually inevitable considering the enhanced prevalence of diabetes and chemotherapeutic treatment of cancers, as well as the "graying" of the population of the United States as advanced age contributes to PN (demonstrated by an enhanced incidence to approximately 15% in the population over forty years of age). Experiment #2 investigated the contribution of neuromuscular control about the ankle to postural steadiness in subjects with peripheral neuropathy as compared to young healthy and older healthy subjects. The most robust correlations force control and postural stability were found in the peripheral neuropathy patients. Stroke is a leading cause of long-term adult disability in the United States which often leads to neuromuscular dysfunction of the upper limb. An element of great importance to survivors of stroke is quality of life in the face of neuromuscular dysfunction. A decreased capacity, or outright inability, to perform functional tasks such as light housework, cooking, bathing and dressing oneself is associated with an increased risk for depression and may necessitate enhanced care such as that found while living with family or in assisted-living communities. Conventional modes of stroke rehabilitation typically yield only modest improvements in upper extremity function. Stroke rehabilitation techniques must be enhanced to afford a greater quality of life to survivors of stroke. Experiments #3 and #4 utilized repetitive transcranial magnetic stimulation as an experimental treatment for stroke rehabilitation. In Experiment #3, survivors of stroke were randomized to either daily repetitive transcranial magnetic stimulation immediately followed constraint induced therapy or an identical treatment in which sham stimulation was used in place of repetitive transcranial magnetic stimulation. The underlying logic of this investigation was that magnetic stimulation of the cortex would enhance neuroplasticity, thereby enhancing recovery. Though repetitive transcranial magnetic stimulation was found to boost excitability at the level of the motor cortex as opposed to sham stimulation, few functional results were noted. Experiment #4 provided repetitive transcranial magnetic to two groups of stroke survivors, one of which triggered the stimulation by surface electromyogram activity at the first dorsal interosseous while the second group received transcranial magnetic stimulation passively. Results similar to those in Experiment #3 were noted in that the triggered stimulation proved to increase cortical excitability (and inhibition, in this case) as compared to passive stimulation while few differences in motor function were found. The findings of these four studies improve the characterization of aging, peripheral neuropathy, and stroke. More importantly, these findings are likely to contribute to future treatments and rehabilitation techniques with the goal of improved neuromuscular function thereby improving quality of life.