Plasticity of Trunk Motor Cortex as a result of Spinal Cord Injury and Robot Rehabilitation Training

Abstract

Cortex is believed to have the necessary substrate to manifest plasticity following manipulations of sensorimotor experience, peripheral or spinal cord injury (SCI). One common model for studying SCI is a complete low thoracic transection in rats resulting in total paraplegia. Complete thoracic SCI induces significant cortical reorganization, such as expansion of forelimb sensory map into the deafferented cortex and expansion of motor representation of hand and proximal muscles. Trunk motor control is crucial after SCI and several rehabilitative strategies are aimed at enhancing trunk stabilization and postural control. How the trunk motor cortex reorganizes after SCI is not clear. Recently using trunk based robot rehabilitation we showed that SCI rats can significantly improve function. Underlying cortical mechanisms associated with successful recovery of function with robot rehabilitation are not completely understood. To this end, we used intracortical microstimulation to examine motor representations in the cortex of SCI rats. We first examined plasticity of trunk motor cortex after chronic adult SCI. We next investigated the effects of robot rehabilitation training on the plasticity of trunk motor cortex in adult SCI rats and adult rats with neonatal SCI. Lastly, we investigated the importance of trunk sensorimotor cortex in mediating recovery of function with robot rehabilitation in adult rats with neonatal SCI through cortical lesion studies. Our results suggest that chronic adult SCI induces significant reorganization of trunk motor cortex. This results in formation of novel synergies between trunk and forelimb and between different trunk segments. Passive (non-stepping) rehabilitation training of adult SCI rats does not induce any measurable plastic changes in trunk motor cortex. Successful robot rehabilitation training of adult rats with neonatal SCI induces significant reorganization of the trunk motor cortex including fractionation and emergence of novel complex muscle synergies within trunk motor cortex. Bilateral lesions to the trunk sensorimotor cortex in adult rats with neonatal SCI disrupts the sensorimotor integration associated with robot training resulting in lack of improvement over the duration of training along with no measurable plastic changes in the cortex. Taken together our findings imply significant reorganization of trunk motor cortex with SCI and successful rehabilitation training.%%%%Ph.D., Biomedical Engineering – Drexel University, 2013