Plasticity and alterations of trunk motor cortex following spinal cord injury and non-stepping robot and treadmill training

Abstract

Spinal cord injury (SCI) induces significant reorganization in the sensorimotor cortex. Trunk motor control is crucial for postural stability and propulsion after low thoracic SCI and several rehabilitative strategies are aimed at trunk stability and control. However little is known about the effect of SCI and rehabilitation training on trunk motor representations and their plasticity in the cortex. Here, we used intracortical microstimulation to examine the motor cortex representations of the trunk in relation to other representations in three groups of chronic adult complete low thoracic SCI rats: chronic untrained, treadmill trained (but 'non-stepping') and robot assisted treadmill trained (but 'non-stepping') and compared with a group of normal rats. Our results demonstrate extensive and significant reorganization of the trunk motor cortex after chronic adult SCI which includes (1) expansion and rostral displacement of trunk motor representations in the cortex, with the greatest significant increase observed for rostral (to injury) trunk, and slight but significant increase of motor representation for caudal (to injury) trunk at low thoracic levels in all spinalized rats; (2) significant changes in coactivation and the synergy representation (or map overlap) between different trunk muscles and between trunk and forelimb. No significant differences were observed between the groups of transected rats for the majority of the comparisons. However, (3) the treadmill and robot-treadmill trained groups of rats showed a further small but significant rostral migration of the trunk representations, beyond the shift caused by transection alone. We conclude that SCI induces a significant reorganization of the trunk motor cortex, which is not qualitatively altered by non-stepping treadmill training or non-stepping robot assisted treadmill training, but is shifted further from normal topography by the training. This shift may potentially make subsequent rehabilitation with stepping longer or less successful.

A simplified method of walking track analysis to assess short-term locomotor recovery after acute spinal cord injury caused by thoracolumbar intervertebral disc extrusion in dogs

“…Functional reorganization of the sensory and motor cortex occurs after SCI, allowing for increased representation of the trunk and thoracic limbs, and structural reorganization of damaged motor pathways in the form of increased collateral sprouting of the corticospinal pathway occurs to increase connections in the cervical spinal cord immediately and weeks after injury (Fouad et al, 2001; Bazley et al, 2014; Oza and Giszter, 2014; Yagüe et al, 2014). Furthermore, changes in thoracic limb and trunk activity in rodent models of thoracic SCI have been previously demonstrated, such as increased thoracic limb and back extensor muscle activity, increased stepping frequency of the thoracic limbs, increased weight bearing in the thoracic limbs, and increased peak vertical forces of the thoracic limbs (Webb and Muir, 2002; Ballermann et al, 2006).…”

Enhancing neural activity to drive respiratory plasticity following cervical spinal cord injury

“…Even a localized event (e.g. SCI) can result in plasticity through the brain, brainstem, spinal cord, peripheral nerves and muscle (Bezdudnaya et al, 2014; Oza and Giszter, 2014, 2015; Raineteau and Schwab, 2001). Another important consideration is that neuroplastic changes do not always translate to functional improvements and may even result in erroneous and detrimental (maladaptive) functions (e.g.…”

Cortical Reorganization of Sensorimotor Systems and the Role of Intracortical Circuits After Spinal Cord Injury

“…Therefore, for meaningful functional recovery after injury to occur, mechanisms of cortical plasticity will be required for the cortex to relearn previous motor patterns using an altered motor pathway. Humans, primates, and rodents all show changes in cortical motor maps after spinal cord injury [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72]. In humans with spinal cord injury, there is increased activity in existing and novel areas within motor, somatosensory, and parietal cortex, as well as in the thalamus, basal ganglia, and cerebellum during movement execution, in comparison to controls [73][74][75][76][77].…”