Control of Ankle Dorsiflexion in Persons with Spinal Cord Injury: Neurophysiology and Neuromodulation via Afferent Stimulation Público
Hope, Jasmine (Fall 2022)
Abstract
Diminished ankle control impedes walking ability in persons with spinal cord injury (SCI). Although some neurological mechanisms of this deficit are known in other populations, there is limited evidence of the pathophysiology of SCI as it relates to both dorsiflexor volitional activation and plantar-flexor spasticity. Furthermore, as noninvasive afferent stimulation therapies are increasingly utilized in rehabilitative therapy, it is important to understand how to optimize these tools to address diminished ankle control. As ankle control is heavily influenced by corticospinal tract descending drive and spinal pattern-generating circuits in a task-dependent manner, the impact of neuromodulatory techniques must be examined across different tasks. Therefore the purpose of my dissertation was to 1) synthesize what is known about the neurophysiological mechanisms of dorsiflexor control after SCI, 2) utilize neuromodulatory techniques that target those mechanisms to determine their persistent impacts on dorsiflexor control, and 3) assess dorsiflexor control across different tasks to distinguish the role of these neurophysiological mechanisms in those tasks, in persons with SCI.
In Chapter 2, we synthesized what was known about the contribution of corticospinal tract descending drive and spinal reflex circuit modulation to disrupted ankle control. In Chapter 3, we determined if there were persistent effects of different doses of robust noninvasive afferent stimulation, in the form of whole body vibration, on dorsiflexion during swing phase of walking and plantar-flexor spinal reflex modulation. Finally, in Chapter 4, we examined the existence of a persistent impact of combined locomotor training and transcutaneous spinal stimulation on dorsiflexion during both the swing phase of walking and a volitional task in participants with SCI.
This dissertation has established 1) a relationship between neurophysiological measures with volitional ankle control and spasticity, 2) whole body vibration and transcutaneous spinal stimulation do not have a persistent impact on dorsiflexor control during walking or volitional activation, but locomotor training may have a persistent impact on these outcomes, and 3) corticospinal descending drive is important for dorsiflexor activation during walking in persons with SCI. The above findings are important steps toward the optimization of rehabilitative therapy in persons with diminished ankle control after SCI.
Table of Contents
Chapter 1: Control of dorsiflexor activation after SCI: neurophysiological mechanisms and neuromodulation of foot drop and ankle clonus
Statement of the Problem: Lack of Dorsiflexor Control in Persons with SCI ................................... 1
What We Know: Neurophysiological Mechanisms of Dorsiflexor Control ...................................... 4
Addressing the Problem: Noninvasive Afferent Stimulation to Promote Neuromodulation ............. 8
Filling the Gaps in Knowledge: Dissertation ..................................................................................... 11
Chapter 2: Disrupted ankle control and spasticity in persons with spinal cord injury: the association between neurophysiologic measures and function. A scoping review
Introduction ........................................................................................................................................ 14
Materials and Methods ....................................................................................................................... 16
Results ................................................................................................................................................ 19
Discussion .......................................................................................................................................... 23
Conclusions ........................................................................................................................................ 28
Chapter 3: Impact of Whole Body Vibration on Dorsiflexion during Swing Phase and Plantar Flexor Reflex Modulation in Persons with SCI
Introduction ........................................................................................................................................ 38
Materials and Methods ....................................................................................................................... 39
Results ................................................................................................................................................ 44
Discussion .......................................................................................................................................... 45
Conclusions ........................................................................................................................................ 46
Chapter 4: Assessment of dorsiflexion ability across tasks in persons with subacute SCI after combined locomotor training and transcutaneous spinal stimulation
Introduction ........................................................................................................................................ 52
Materials and Methods ....................................................................................................................... 54
Results ................................................................................................................................................ 59
Discussion .......................................................................................................................................... 61
Conclusions ........................................................................................................................................ 65
Chapter 5: Implications and future directions of neuromodulation techniques targeting neurophysiological mechanisms of dorsiflexor control after SCI.
Chapter 2: Relationship between Corticospinal Descending Drive and Spinal Reflex Circuitry in Dorsiflexor Control and Plantar-Flexor Spasticity ............................................................................ 71
Chapter 3: Impacts of Robust Afferent Stimulation on Dorsiflexion during Swing Phase and Spinal Reflex Modulation .................................................................................................................. 72
Chapter 4: Persistent Effects of Combined Locomotor Training and Transcutaneous Spinal Stimulation on Dorsiflexion across Tasks in Persons with Spasticity ............................................... 73
Conclusions ........................................................................................................................................ 74
References .........................................................................................................................................75
Appendix I: List of Abbreviations .................................................................................................. 83
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