Project Summary/Abstract
Chronic walking impairments such as decreased walking speed, endurance, and independence are common
after stroke and limit physical activity, quality of life, and community involvement. These walking impairments
contribute to high healthcare costs and the development of secondary disabilities. Walking impairments tend to
persist despite gait rehabilitation, partly because we lack a comprehensive understanding of which brain
pathways contribute to lower limb and walking recovery after stroke. Emerging evidence suggests that
ipsilaterally-descending motor pathways from the non-lesioned hemisphere to the stroke-affected limb,
specifically the corticoreticulospinal tract, may be enhanced. However, the measurement tools used in prior work,
when considered in isolation, provide limited insight into whether this pathway is functional enhanced and
contributes to improved lower limb function. The primary objective of this proposal is to address this question
with the long-term goal of improving gait rehabilitation after stroke by identifying recovery-related motor pathways
that can be targeted. Our central hypothesis is that the corticoreticulospinal tract from the non-lesioned brain
hemisphere to the more affected limb will be enhanced after stroke. The secondary objective of this proposal is
to determine whether the strength of the corticoreticulospinal tract from the non-lesioned brain hemisphere
influences lower limb motor control. To achieve the objectives of this proposal, two specific aims will be tested
in individuals with chronic stroke with a range of impairment. In Aim 1, we will develop a multi-dimensional
estimate of whether the corticoreticulospinal tract is enhanced after stroke by combining three measures used
in prior research: functional magnetic resonance imaging (non-lesioned brain activation), diffusion tensor imaging
(structural integrity), and transcranial magnetic stimulation (functional excitability). In Aim 2, the association
between the strength of the corticoreticulospinal tract from the non-lesioned hemisphere and lower limb motor
control will be assessed. This analysis will account for measures of stroke severity (lesion load and lower limb
impairment). The proposed work would be the first to use a multifaceted approach to comprehensively and
rigorously assess whether brain pathways from the non-lesioned hemisphere to the stroke-affected lower limb
are enhanced after stroke. Results from this work will improve our understanding of the brain pathways that
contribute to walking recovery after stroke, essential information for improving walking rehabilitation. The
proposed work will also provide insight into how stroke impairment influences the mechanisms of recovery and
the optimal rehabilitative strategy. Support for the central hypothesis will be a major breakthrough that supports
the potential for neuromodulation applied to non-lesioned brain pathways pathways to lead to improvements in
walking recovery after stroke. Improvements in walking rehabilitation that result from the proposed work could
lead to substantial reductions in chronic walking impairment, disability, and societal cost of stroke.
