Lisa Kogan

Date of Graduation

2017

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Sergiy Yakovenko

Committee Co-Chair

Valeriya Gritsenko

Committee Member

Yu Gu

Abstract

The coordination between signals from cortical structures and spinal segmental pathways responsible for the control of locomotion remains a contentious issue in human motor control. The signals are known to be integrated, but the nature of these neural calculations is unknown. To understand these interactions in humans, noninvasive cortical stimulation techniques can be combined with detailed analyses of muscle activity patterns in locomotor tasks.;In this study, I tested the relationship between corticospinal inputs and the forward velocity of each limb. Transcranial magnetic stimulation (TMS) was used to elicit motor evoked potentials (MEPs) in 12 healthy human volunteers during locomotion on a split-belt treadmill, allowing for the evaluation of corticospinal excitability (CSE) throughout 4 gait tasks. Participants were instrumented with electromyography (EMG) sensors to collect activity of representative muscles of both lower limbs. The velocity conditions were limited to two symmetrical tasks, with both belts moving at either 1 or 1.25 m/s, and two asymmetrical tasks, with one belt moving at 1 and the other at 1.25 m/s. During each trial, a double cone coil was used to stimulate the area of the primary motor cortex (M1) associated with voluntary control of the lower limbs, throughout different phases of the step cycle. Real-time stimulation targeting was accomplished using tracking hardware and neuronavigation software, and the relative location of stimulation was automatically saved to ensure consistency between trials. The MEP epochs within the EMG signals were detected using an outgoing TMS synchronization pulse. Individual MEP magnitudes were normalized to the pre-stimulation muscle activity for comparison, and were binned according to step cycle phase.;Statistical tests were conducted using intra- and inter-subject group means from different velocity conditions, and phases of the step cycle. The relative locations of stimulation were also analyzed to describe the accuracy and precision of stimulation across trials. The non-normalized MEP amplitude was correlated with the muscle activity during control steps. The pattern of MEP modulation supported the hypothesis that CSE contains information about limb velocity.

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