Plasticity associated changes in cortical somatosensory evoked potentials following spinal cord injury in rats

Spinal cord injury (SCI) causes a number of physiological and neurological changes resulting in loss of sensorimotor function. Recent work has shown that the central nervous system is capable of plastic behaviors post-injury, including axonal regrowth and cortical remapping. Functional integrity of afferent sensory pathways can be quantified using cortical somatosensory evoked potentials (SSEPs) recorded upon peripheral limb stimulation. We implanted 15 rats with transcranial screw electrodes and recorded SSEPs from cortical regions corresponding to each limb before and after a mild or moderate contusion injury. We report a post-injury increase in the mean amplitude of cortical SSEPs upon forelimb stimulation. SSEP amplitudes for mild and moderate SCI groups increased by 183%±95% and 107%±38% over baseline, respectively, while hindlimb SSEPs decreased by 58%±14% and 79%±4%. In addition, we report increased SSEP amplitude measured from the anatomically adjacent hindlimb region upon forelimb stimulation (increase of 90%±19%). Our results show that previously allocated hindlimb cortical regions are now activated by forelimb stimulation, suggesting an expansion in the area of cortical forelimb representation into hindlimb regions after an injury. This result is indicative of adaptive plasticity in undamaged areas of the CNS following SCI.