Neuronal mechanisms underlying retraining of walking after incomplete spinal cord injury

  • Author / Creator
    Zewdie, Ephrem Takele
  • Inhibitory feedback from sensory pathways is important for controlling movement. In this thesis we characterize a long-latency inhibitory spinal pathway to ankle flexors that is activated by low-threshold, homonymous afferents. In non-injured participants, this pathway was activated by both descending and sensory inputs. A spinal origin of this inhibition was confirmed by reproducing its effect on evoked responses from direct activation of corticospinal pathways. We propose that inhibitory feedback from spinal networks activated by low-threshold homonymous afferents helps regulate the activation of flexor motoneurons by the corticospinal pathways. In the second part of the thesis we compared changes in corticospinal and spinal pathways in response to endurance and skill locomotor training in participants with incomplete, chronic spinal cord injury. Both forms of training increased the maximum evoked potential (MEPmax) elicited by transcranial magnetic stimulation over the motor cortex, but only in tibialis anterior muscles that had smaller MEPmax values before training, no matter when the specific type of training was performed. Endurance and precision training also increased the excitability of inhibitory spinal networks, as demonstrated by increases in the long-latency, homonymous spinal inhibition described above and by increases in the inhibitory component of the cutaneomuscular reflex. The increase in the descending activation of the spinal cord and the increase in excitability of inhibitory spinal networks may mediate the improved volitional control of walking and reduction of involuntary muscle spasticity, respectively, that are observed in response to intensive motor training.

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  • Graduation date
  • Type of Item
  • Degree
    Doctor of Philosophy
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    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
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  • Institution
    University of Alberta
  • Degree level
  • Department
  • Supervisor / co-supervisor and their department(s)
  • Examining committee members and their departments
    • Calancie, Blair (Neurosurgery)
    • Chan, Ming (Physical Medicine & Rehabilitation)
    • Gorassini, Monica (Biomedical Engineering)
    • Collins, Dave (Physical Education)
    • Yang, Jaynie (Rehabilitation Medicine)
    • Willman, Alan (Biomedical Engineering)
    • Jones, Kelvin (Physical Education)