With the help of robot-assisted rehabilitation and electrochemical spinal cord stimulation, rats with clinically-relevant spinal cord injury regain control of their otherwise paralyzed limbs. But how do brain commands – about walking, swimming and stair-climbing – bypass the injury and still reach the spinal cord to execute these complex tasks? EPFL scientists have observed for the first time that the brain reroutes task-specific motor commands through alternative pathways originating in the brainstem and projecting to the spinal cord. The therapy triggers the growth of new connections from the motor cortex into the brainstem and from the brainstem into the spinal cord, thus reconnecting the brain with the spinal cord below the injury. The results are published in Nature Neuroscience March 19th.
Cortico–reticulo–spinal circuit reorganization enables functional recovery after severe spinal cord contusion
Severe spinal cord contusions interrupt nearly all brain projections to lumbar circuits producing leg movement. Failure of these projections to reorganize leads to permanent paralysis. Here we modeled these injuries in rodents. A severe contusion abolished all motor cortex projections below injury. However, the motor cortex immediately regained adaptive control over the paralyzed legs during electrochemical neuromodulation of lumbar circuits. Glutamatergic reticulospinal neurons with residual projections below the injury relayed the cortical command downstream. Gravity-assisted rehabilitation enabled by the neuromodulation therapy reinforced these reticulospinal projections, rerouting cortical information through this pathway. This circuit reorganization mediated a motor cortex–dependent recovery of natural walking and swimming without requiring neuromodulation. Cortico–reticulo–spinal circuit reorganization may also improve recovery in humans.