In partial fulfillment of the requirements for the degree of

Doctor of Philosophy in Applied Physiology

In the

School of Biological Sciences

Shea McMurtry

Will defend her dissertation

A novel approach to restore proprioceptive feedback following spinal cord injuries using eccentric training

Friday, April 15th, 2022

1:00 PM EST

In person: Applied Physiology Building (555 14th st.), Room 1253

Virtual: https://bluejeans.com/282178122/2722

 Thesis Advisor:

T Richard Nichols, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Committee Members:

Tim Cope, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Boris Prilutsky, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Dena Howland, Ph.D.

Dept. of Neurological Surgery and Anatomical Sciences

University of Louisville

Mark Lyle, Ph.D.

School of Medicine

Emory University

Abstract

Incomplete spinal cord injuries (SCI) lead to a variety of motor deficits including problems with ambulation. A further understanding of the pathophysiology leading to these deficits is required to develop therapies. Previous research in our lab using the decerebrate preparation shows that inhibitory force feedback (iFFB) is upregulated and distributed across hindlimb muscles in one distinct pattern following lateral hemisection (LHX). Spinally intact animals show mostly balanced flexible patterns of iFFB with a different pattern during stepping. Data from previous studies also support the hypothesis that inhibitory force feedback is increased during walking down slope, a complex task that features eccentric work of extensor muscles.

This project is a component of a comprehensive study of the effects of partial spinal cord injury on motor behavior and the underlying mechanisms, and possible rehabilitation strategies. The efficacy and specificity of eccentric training in normalizing the organization of proprioceptive feedback and its relationship to improvements in motor behavior were tested. This was conducted in conjunction with Dr. Dena Howland and her lab, who performed the spinal injuries, training, kinematic analyses and histology. Eccentric muscle contractions are essential for walking over different kinds of terrain and are prominent during the weight acceptance (E2) phase. Animals with LHX showed an overall increased flexion throughout E1 and E2 as well as changes in limb coordination possibly due to a decrease in limb stiffness from the amplified force feedback.

This project used mechanographic methods to investigate changes in reflex stiffness and heterogenic force feedback following a LHX across various training protocols. The injury led to an increase in inhibitory force feedback onto ankle extensors, and a delayed increase in the stretch reflexes in the same muscles. Both eccentric and level training induced plasticity in reflex pathways, but eccentric training was more effective in returning the strength and distribution of proprioceptive feedback toward that observed in spinally intact animals. These results further suggest that the reorganization of the force feedback network is likely to play a major role mediating the motor deficits observed during the stance phase of locomotion, and that eccentric training can restore the animal’s ability to modulate proprioception during complex tasks following spinal cord injury.