Compensatory role of the cortico-rubro-spinal tract in motor recovery after stroke

Abstract

Objectives:Studies on nonhuman primates have demonstrated that the cortico-rubro-spinal system can compensate for damage to the pyramidal tract (PT). In humans, so-called alternate motor fibers (aMF), which may comprise the cortico-rubro-spinal tract, have been suggested to play a similar role in motor recovery after stroke. Using diffusion tensor imaging, we examined PT and aMF in the context of human motor recovery by relating their microstructural properties to functional outcome in chronic stroke patients.Methods: PT and aMF were reconstructed based on their origins in primary motor, dorsal premotor, and supplementary motor cortices in 18 patients and 10 healthy controls. The patients' degree of motor recovery was assessed using the Wolf Motor Function Test (WMFT).Results: Compared to controls, fractional anisotropy (FA) was lower along ipsilesional PT and aMF in chronic stroke patients, but clusters of higher FA were found bilaterally in aMF within the vicinity of the red nuclei. FA along ipsilesional PT and aMF and within the red nuclei correlated significantly with WMFT scores. Probabilistic connectivity of aMF originating from ipsilesional primary motor cortex was higher in patients, whereas the ipsilesional PT exhibited lower connectivity compared to controls. Conclusions:The strong correlations observed between microstructural properties of bilateral red nuclei and the level of motor function in chronic stroke patients indicate possible remodeling during recovery. Our results shed light on the role of different corticofugal motor tracts, and highlight a compensatory function of the cortico-rubro-spinal system which may be used as a target in future restorative treatments. Neurology ® 2012;79:515-522 GLOSSARY aMF ϭ alternate motor fibers; DTI ϭ diffusion tensor imaging; FA ϭ fractional anisotropy; FWE ϭ family-wise error; M1 ϭ primary motor cortex; PMd ϭ dorsal premotor cortex; PT ϭ pyramidal tract; ROI ϭ region of interest; SMA ϭ supplementary motor area; WMFT ϭ Wolf Motor Function Test.Motor impairment after stroke has been related to the structural and functional integrity of corticospinal tracts.1 Besides the pyramidal tract (PT), so-called alternate motor fibers (aMF) have been suggested to play a role in modulating recovery after stroke. Based on animal studies, it has been hypothesized that aMF comprise the cortico-rubro-spinal and cortico-reticulospinal systems.2-4 However, anatomic evidence of those systems in man is sparse.1 Diffusion tensor imaging (DTI) allows for the reconstruction of monosynaptic and polysynaptic fiber bundles, 5,6 and lesion-induced alterations of dedicated tracts can be quantified 7 and related to impairment of motor function after stroke. 8 -10 It has been demonstrated that DTIderived measures of both PT and aMF explain more of the variance in motor outcome than the PT alone.3 However, the methodology applied in the latter study did not allow for the detection of regional microstructural alterations so that no further inferences on aMF and their impact on reco...

Differential Adaptation of Descending Motor Tracts in Musicians

“…In previous studies, aMF showed adaptations in cases of severe lesions to the PT (Belhaj-Saif and Cheney 2000; Lindenberg et al 2010;Rüber et al 2012). Overall, this would support the notion that the PT might be more involved in the execution and control of finegrained distal finger movements, while aMF might be more involved in proximal motor control and that aMF only show adaptations in response to distal motor requirements when the PT system is damaged (Canedo 1997;Lemon 2008).…”

“…To reconstruct different portions of PT and aMF according to their origins in primary and nonprimary motor cortices, 3 different regions of interest (ROIs) were drawn on the same axial slice in the subcortical white matter Rüber et al 2012). The border between primary (M1) and dorsal premotor cortices (PMd) cannot be easily determined since their cytoarchitectonic boundaries do not correspond to gross-anatomic landmarks (Geyer et al 2000).…”

“…These aMF might comprise the cortico-rubro-spinal and the cortico-reticulo-spinal tracts (Canedo 1997). They have been found to play an important role and show adaptations in motor recovery after lesions to the PT (Lindenberg et al 2010;Rüber et al 2012). The aims of our study were to test the hypotheses that (1) diffusivity measures of PT and aMF would show characteristic differences between keyboard players, string players, and nonmusicians and that (2) diffusivity measures of PT and aMF would be related to functional motor performance.…”

Emergent properties of neural repair: elemental biology to therapeutic concepts

“…Human studies show that the structure of specific white matter tracts are associated with functional recovery after stroke, and can respond to behavioral activity 35, 36. The relationship of white matter tract structure and axonal sprouting has not been determined.…”

“…The relationship of white matter tract structure and axonal sprouting has not been determined. Human studies image large white matter tracts and, through the diffusion of water, their myelination state and their directional organization 35, 37. Rodent studies image truly small axonal collaterals and fine synaptic terminations within the cervical spinal cord 27, 28, 29, 30, 31.…”