Date of Award

Summer 2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biomedical Engineering

First Advisor

Sheila Schindler-Ivens

Second Advisor

Brian D Schmit

Third Advisor

Sylvain Baillet

Abstract

The role of the cortex during locomotion remains unclear, but recent advances in neural imaging technologies have aided in developing ways to measure brain activity during motor tasks. One method is by measuring activations produced by neural oscillations which have been associated with a variety of human behaviors, from sleep and rest to cognitive actions and movement. The physiological and functional methods in which oscillations contribute to cortical control are still largely unknown. In this study, we aim to expand that knowledge by examining human cortical activity in the sensory and motor cortices during pedaling using magnetoencephalography (MEG). We hypothesized that, if the sensory and motor cortices are important for controlling locomotion, then the MEG signal would differ during pedaling as compared to rest and would be modulated with the phase of the pedaling cycle. Moreover, if locomotor-related brain activity is solely caused by sensory feedback, then the MEG signal would be the same during active and passive pedaling. We scanned eight healthy subjects using MEG while they pedaled a custom-made pedaling device. The subjects’ magnetocortical activity was measured in two minute recordings during rest, continuous, self-paced active pedaling, and passive pedaling. The passive condition consisted of the subject relaxing their leg muscles while the experimenter pedaled the device for them at a velocity matching that subject’s active pedaling bout. Task-dependent magnetocortical activity was examined in the primary sensorimotor cortex (M1 and S1), supplemental motor area (SMA), and premotor area (PMA). The power spectrum of the MEG signal during the different tasks was extracted using a Welch periodogram to examine the frequency content throughout each task. The power in the alpha and beta bands of all regions of interest decreased significantly during active and passive pedaling as compared to rest. No significant difference was found between any of the tasks in the gamma band. The temporal pattern of the beta frequency band was also examined across the pedaling cycle by performing a time-frequency decomposition using a Morlet wavelet. Both pedaling conditions demonstrated modulation of the beta band at twice the pedaling frequency. These fluctuations were not found in the rest condition. Our results showed that the brain becomes engaged during pedaling as compared to rest. The magnetocortical activity is different across the movement cycle, suggesting that the brain has input into the regulation of locomotor-like movement. There is also a strong sensory component during movement since the active and passive pedaling conditions are similar.