Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2017 - 20202

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Author: search.filters.author.Rafiee, ShakibaSubject: search.filters.subject.Neurosciences

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    NEURAL FEEDBACK CONTRIBUTION TO HUMAN LOCOMOTION CONTROL
    (2020) Rafiee, Shakiba; Miller, Ross H.; Kiemel, Tim; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The human nervous system stabilizes locomotion by continuously correcting for deviations away from the desired gait pattern through making transient changes to muscle excitations. We refer to this correction process as “muscle modulation”. It remains unknown how muscle modulations are implemented in the larger framework of human neuromuscular control to achieve stability. Such knowledge has implications across various health and engineering fields. Systematic identification of the properties of the nervous system can provide insight into the role that different muscle modulations play in human walking. Additionally, mathematical models of human walking can be used to test the validity of different neural controllers. In this thesis, we devised three studies to further our understanding of the role different muscle modulations play in human walking and hypothesize the neural mechanisms involved in producing them. In study one, we investigated the role of the ankle dorsiflexor muscle, tibialis anterior, modulation in the control and stability of human walking. Previous research from our lab has suggested a novel role for the tibialis anterior in speed control during early stance. To investigate this role, we imposed a restriction on ankle dorsiflexion using a taping method, which limited the ability of this muscle to accelerate the body forward during early stance. We characterized the kinematic and muscular responses of this “restricted” walking to mechanical perturbations and compared the results with those from “normal” human walking. Our results support the idea that early stance modulation of tibialis anterior muscle regulates speed control. In studies two and three, we used mathematical models of human walking to investigate the neural mechanisms involved in foot-placement. In study two, we examined whether a model of human locomotion that is purely controlled by spinal reflex mechanisms can produce muscle modulations observed in human locomotion. In study three, we developed a model of human walking and examined its response to mechanical perturbations of the leg. Together these studies provided insight into the types of neural mechanisms the human nervous system uses to stabilize walking. We observed that gated reflex mechanisms can produce some of the human responses to external perturbations, but not all.
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    Lower-Body Mechanical Perturbation of Gait to Identify Neural Control
    (2017) Rafiee, Shakiba; Kiemel, Tim; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Neural feedback plays a key role in maintaining locomotor stability in face of perturbations. In this study, we systematically identified properties of neural feedback that contribute to stabilizing human walking by examining how the nervous system responds to small kinematic deviations away from the desired gait pattern. We applied small continuous mechanical perturbation, forces at the ankles, as well as small continuous sensory perturbation, movement of a virtual visual scene, in order to compare how neural feedback responds to actual and illusory kinematic deviations. Computing phase-dependent impulse response functions (φIRFs) that describe kinematic and muscular responses to small brief perturbations (impulses), enabled us to identify critical phases of the gait cycle when the nervous system modulates muscle activity. In particular, our results suggest that an early-stance modulation of anterior leg-muscles is a general control mechanism that serves multiple functions, including controlling walking speed and compensating for errors in foot placement.