Spinal cord stimulation modulates post-synaptic inhibition to improve arm neuromotor control after chronic stroke

Epidural spinal cord stimulation has been shown to be a promising neurotechnology to improve upper limb function in people affected by stroke. It is well established that spinal cord stimulation (SCS) targeting the dorsal root entry zone increases excitatory drive to α-motoneurons via the monosynaptic reflex pathway. However, the effects of SCS on inhibitory neural pathways remain unexplored. We hypothesized that SCS improves the neuromotor control of arm movement by strengthening both excitatory and inhibitory circuit function. We show in three individuals with post-stroke motor symptoms that SCS enhances postsynaptic Ia reciprocal inhibition. These changes correlate with enhanced muscle coordination and arm kinematics, resulting in smoother and faster trajectories. Our study provides further insights into the neural targets of spinal cord stimulation and the use of this technology to treat post-stroke motor deficits. This study was registered at ClinicalTrials.gov (NCT04512690).