Spinal nociceptive and non-nociceptive processing of cutaneous afferent input in people with chronic incomplete...

In people with chronic spinal cord injury (SCI), the excitability of spinal reflexes of muscle afferent origins changes, likely contributing to sensorimotor impairments (e.g., spasticity). In contrast to changes in muscle afferent reflexes that are well-recognized, little is known about potentially altered processing of nociceptive and non-nociceptive cutaneous input in chronic incomplete SCI. Thus, this study aimed to systematically examine spinal processing of nociceptive and non-nociceptive cutaneous input in people with sensorimotor impairments due to chronic incomplete SCI, using non-invasive cutaneous nerve stimulation. To characterize non-nociceptive processing, cutaneous reflexes to non-painful stimulation was measured in the triceps surae; we found that the soleus reflexes were smaller and frequently inhibitory when they should be excitatory, suggesting altered processing of non-noxious cutaneous input in people with sensorimotor impairments due to chronic SCI. In parallel, when the persistence of pain pathway activation was assessed near the pain threshold, it was found robust and could be enhanced more with a higher input frequency. These key findings are discussed in the context of altered spinal neurophysiology in chronic incomplete SCI. This study supports potential utilities of electrical nerve stimulation in probing spinal non-nociceptive and nociceptive pathways in persons with SCI.