Moving toward elucidating alternative motor pathway structures post-stroke: the value of spinal cord neuroimaging

Abstract

Stroke results in varying levels of motor and sensory disability that have been linked to the neurodegeneration and neuroinflammation that occur in the infarct and peri-infarct regions within the brain. Specifically, previous research has identified a key role of the corticospinal tract in motor dysfunction and motor recovery post-stroke. Of note, neuroimaging studies have utilized magnetic resonance imaging (MRI) of the brain to describe the timeline of neurodegeneration of the corticospinal tract in tandem with motor function following a stroke. However, research has suggested that alternate motor pathways may also underlie disease progression and the degree of functional recovery post-stroke. Here, we assert that expanding neuroimaging techniques beyond the brain could expand our knowledge of alternate motor pathway structure post-stroke. In the present work, we will highlight findings that suggest that alternate motor pathways contribute to post-stroke motor dysfunction and recovery, such as the reticulospinal and rubrospinal tract. Then we review imaging and electrophysiological techniques that evaluate alternate motor pathways in populations of stroke and other neurodegenerative disorders. We will then outline and describe spinal cord neuroimaging techniques being used in other neurodegenerative disorders that may provide insight into alternate motor pathways post-stroke.

Keywords: alternate motor pathways; imaging; reticulospinal; rubrospinal; stroke.

Figure 1

(A) Pictural representation of common tracts associated with recovery following stroke. Image representations were adapted from (–38). (B) Atlas-based probabilistic tract reconstruction utilizing FA and Intra-Cellular Volume Fraction (ICVF) with the Spinal Cord Toolbox for visualizing alternate motor pathways throughout the spinal cord (35, 36, 39). Images of the cervical region were processed using linear interpolation, and the alpha parameter was modified based on tract intensity.

Figure 2

Anatomical tracts, neuroimaging analysis, and 3D reconstruction of the corticospinal tract and alternate motor tracts. Advanced neuroimage processing software, such as FSL for DTI, DSI Studio for DTI Tractography, and AMICO for NODDI, can be employed to quantify diffusion-weighted imaging, determine microstructure properties, and analyze individual tract morphology. All images were from the cervical region and used linear interpolation. The left side depicts the T2 weighted anatomical image with the slice location. The left column shows DTI outputs from SCT processing, MD, FA, and V1. The center illustrates the NODDI processing outputs of isotropic volume fraction (ISOVF; CSF), intra-cellular volume fraction (ICVF; neurite density), and the overlapped representation of neurite density and CSF. On the right are the 3D reconstruction of the CSF (top) and neurite density (center) visualized using FSLeyes. Additionally, the 3D fiber reconstruction of DTI tractography (bottom) is presented using DSIstudio.