Enhanced sensorimotor cortex responsiveness to nonplegic hand stimulation and motor network assembly during recovery after spinal cord injury in primates

Previous studies have reported changes in cortical responses to stimulation of the plegic or nonplegic hand after unilateral neuronal injury. We aimed to investigate the relationship between these responsiveness changes in central sensorimotor systems and functional recovery. Five macaque monkeys underwent lower cervical cord subhemisection surgery. Their hand movements were observed, and longitudinal functional MRI (fMRI) was performed under anaesthesia to assess responses to tactile stimulation of each hand and resting-state connectivity. Eigenvector centrality was computed from resting-state fMRI data to examine network assembly. Following severe paralysis of the ipsilesional hand, four monkeys showed recovery of grasping movements, with an average success rate improving until 16 weeks post-injury. Bilateral sensorimotor hand areas exhibited increased responses to contralesional (nonplegic hand) stimulation 2-5 weeks post-injury, which declined over time. These changes correlated with the centrality of the bilateral premotor cortices and supplementary motor areas. An inverse correlation was observed between responses in the ipsilesional sensorimotor cortex and success rates. These findings suggest that cortical responsiveness enhancement may be caused by post-injury disinhibitory mechanisms involving motor network assembly. Our results indicate that disinhibitory mechanisms can drive large-scale sensorimotor reorganisation, and disinhibition reduction leads to long-term recovery after spinal cord injury in primates.