How plastic are human spinal cord motor circuitries?

Abstract

Human and animal studies have documented that neural circuitries in the spinal cord show adaptive changes caused by altered supraspinal and/or afferent input to the spinal circuitry in relation to learning, immobilization, injury and neurorehabilitation. Reversible adaptations following, e.g. the acquisition or refinement of a motor skill rely heavily on the functional integration between supraspinal and sensory inputs to the spinal cord networks. Accordingly, what is frequently conceived as a change in the spinal circuitry may be a change in either descending or afferent input or in the relative integration of these, i.e. a change in the neuronal weighting. This is evident from findings documenting only task-specific functional changes after periods of altered inputs whereas resting responses remain unaffected. In fact, the proximity of the spinal circuitry to the outer world may demand a more rigid organization compared to the highly flexible cortical circuits. The understanding of all of this is important for the planning and execution of neurorehabilitation.

Long-term motor skill training with individually adjusted progressive difficulty enhances learning and promotes corticospinal plasticity

“…Synaptic connections between descending pyramidal cells and their spinal targets are malleable 81,82 and are a likely substrate for activity-dependent modulation 83 . It is likely that plastic changes on a spinal level contribute to reshaping motor output during skill learning (see 84 for review). Previous findings that short-term ballistic learning potentiates the response to electrical stimulation at the level of the brainstem support the notion that spinal adaptations may contribute to the observed changes in MEP amplitude on the first day of training 85 .…”

Maturation of the Locomotor Circuitry in Children With Cerebral Palsy

“…What are indicators of the spinal cord involvement in CP? First, although it has been argued that the proximity of the spinal circuitry to the outer world may demand a more rigid organization compared to the highly flexible cortical circuits (Christiansen et al, 2017), this statement is valid only to some extent and unlikely for the developing spinal cord. Definitely, the spinal cord is not a simple relay structure for communication between central structures and skeletal musculature but is flexible (Heng and de Leon, 2007), capable of performing coordinate transformations (Fukson et al, 1980;Windhorst, 1996a;Poppele and Bosco, 2003), synapse daily turnover, cell death and atrophy after a spinal cord injury (Dietz and Müller, 2004;Gazula et al, 2004) or after brain damage (Drobyshevsky and Quinlan, 2017).…”

The negotiated equilibrium model of spinal cord function

“…plasticity) throughout life – with growth and ageing, as new behaviours are acquired, and in response to trauma and disease (Mendell, ; Wolpaw & Tennissen, ; Pierrot‐Deseilligny & Burke, ; Wolpaw, ; Christiansen et al . 2017). The recent recognition of this continual spinal cord plasticity raises a critical new question.…”

“…Over the past several decades, it has become clear that the spinal cord, like the rest of the central nervous system (CNS), undergoes activity-dependent change (i.e. plasticity) throughout life -with growth and ageing, as new behaviours are acquired, and in response to trauma and disease (Mendell, 1984;Wolpaw & Tennissen, 2001;Pierrot-Deseilligny & Burke, 2012;Wolpaw, 2012;Christiansen et al 2017). The recent recognition of this continual spinal cord plasticity raises a critical new question.…”