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Author ORCID Identifier

https://orcid.org/0000-0003-4460-4546

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Kinesiology

Year Degree Awarded

2019

Month Degree Awarded

May

First Advisor

Julia T. Choi

Subject Categories

Kinesiology | Motor Control

Abstract

Walking is a complex task that requires precise coordination of many muscles and joints. The nervous system must continually learn how to control gait patterns as changes occur to the body (e.g., injury and fatigue) or environment (e.g., slippery floor). Motor learning refers to processes that improve the spatial and/or temporal accuracy of a movement through motor practice. Although additional hours of practice can improve motor skill performance (online learning), time without additional practice (offline learning) can further enhance motor learning. Consolidation refers to the process by which motor (procedural) memory becomes more robust and stable after the end of a practice session. Recent studies have demonstrated that considerable consolidation may occur, either preferentially or exclusively, during sleep. This is referred to as sleep-dependent consolidation. The aim of this dissertation was to examine the role of sleep in the consolidation in two different locomotor tasks: locomotor sequence learning and locomotor adaptation. In the first study, participants practiced a sequence of visually cued step lengths during forward walking. Participants were subsequently tested, either with an untrained gait pattern (backward walking) using the same visual cues to probe transfer in the perceptual domain, or with the same gait pattern using different visual cues (inverted screen) to probe transfer in the motor domain. Transfer was assessed immediately (immediate transfer), and 12 h later (delayed transfer), following overnight sleep or a period of daytime alertness. We found minimal immediate transfer in the perceptual domain; however, the backward pattern improved by about 10% following a 12-h interval that included sleep. In contrast, the backward pattern only improved by around 1% following a 12-h interval awake. This suggest that sleep was important for delayed generalization of perceptual learning. Transfer in the motor domain was similarly improved over a 12-h interval, with or without sleep, indicating that time-dependent processes were involved in delayed transfer of motor learning. In the second study, participants performed a split-belt treadmill walking task with a 2:1 speed ratio over 15 min of training. Savings (i.e., faster re-adaptation) of the 2:1 split-belt walking pattern were assessed immediately (immediate savings), and again 12 h later (delayed savings) following an awake period (awake group), or an identical period of time that included sleep (sleep group). Participants in the sleep group showed delayed savings in step length symmetry compared with those in the awake group, suggesting that sleep was beneficial for spatial locomotor adaptation. Temporal locomotor adaptations showed immediate savings, but delayed savings were not enhanced after a 12-h awake period or 12-h period that included sleep. In sum, we showed that consolidation of locomotor skills involves both parallel and distinct processes for motor and perceptual learning, as well as spatial and temporal control of gait. Some of these processes appear to preferentially or exclusively operate during sleep. The nervous system’s ability to differentially respond to various training schedules should enable clinicians to tailor rehabilitation regimes for gait recovery while maximizing rehabilitation outcomes and training efficiency. These appear to be of equal or possibly greater importance than the actual amount of practice.

DOI

https://doi.org/10.7275/1sa6-r798

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