A Review on Locomotor Training after Spinal Cord Injury: Reorganization of Spinal Neuronal Circuits and Recovery of Motor Function

Abstract

Locomotor training is a classic rehabilitation approach utilized with the aim of improving sensorimotor function and walking ability in people with spinal cord injury (SCI). Recent studies have provided strong evidence that locomotor training of persons with clinically complete, motor complete, or motor incomplete SCI induces functional reorganization of spinal neuronal networks at multisegmental levels at rest and during assisted stepping. This neuronal reorganization coincides with improvements in motor function and decreased muscle cocontractions. In this review, we will discuss the manner in which spinal neuronal circuits are impaired and the evidence surrounding plasticity of neuronal activity after locomotor training in people with SCI. We conclude that we need to better understand the physiological changes underlying locomotor training, use physiological signals to probe recovery over the course of training, and utilize established and contemporary interventions simultaneously in larger scale research studies. Furthermore, the focus of our research questions needs to change from feasibility and efficacy to the following: what are the physiological mechanisms that make it work and for whom? The aforementioned will enable the scientific and clinical community to develop more effective rehabilitation protocols maximizing sensorimotor function recovery in people with SCI.

Effects of Training Intensity on Locomotor Performance in Individuals With Chronic Spinal Cord Injury: A Randomized Crossover Study

“…Mechanisms underlying improved kinematic coordination deserves further study, but suggests altered neural strategies underlie the observed changes. Indeed, stepping training has been shown to elicit increases in supraspinal 51 and spinal circuits 52 that may contribute to locomotor improvements. These changes may be enhanced with high-intensity training, which can result in the synthesis and release of various trophic factors (e.g., brain-derived neurotrophic factors, or BDNF; for review, please see 53,54 ) that may facilitate neuroplastic alterations 40 .…”

Disrupted Ankle Control and Spasticity in Persons With Spinal Cord Injury: The Association Between Neurophysiologic Measures and Function. A Scoping Review

“…These symptoms include clonus or hyper-reflexive response to afferent input (i.e., stretch, touch, cold temperatures), muscle stiffness (hypertonia), and spontaneous involuntary muscle contractions (spasms) (17,18). The maladaptive changes to the circuits controlling the DF and PF following SCI have been described (19)(20)(21); however, Abbreviations: SCI, spinal cord injury; DF, ankle dorsiflexors; VAC, volitional ankle control; SRC, spinal reflex circuitry; CST, corticospinal tract; H-reflex, Hoffman reflex; MEP, motor evoked potentials; PF, plantar flexors; TMS, transcranial magnetic stimulation. the relationship between decreased CST descending drive and disrupted SRC modulation with volitional ankle control (VAC) (dorsiflexion during gait, toe tapping, etc.)…”

Understanding exercise-dependent plasticity of motoneurons using intracellular and intramuscular approaches

“…Spinal cord transection is surgically performed around the mid-thoracic level, which removes descending input to MNs below that level. After spinal cord transection, the biophysical properties of MNs below the site of the insult undergo significant changes (Smith and Knikou 2016). However, intracellular recordings from cat and rat MNs reveal a paradoxical effect of spinal cord transection on MN excitability.…”