Electrical Stimulation as a Tool to Promote Plasticity of the Injured Spinal Cord

This review discusses the progression and use of electrical stimulation (ES) over time as it pertains to promoting axonal outgrowth and functional recovery post-SCI. It considers four major uses for the study of ES based on the proposed or documented underlying mechanism. The four uses are: using ES to introduce an electric field at the site of injury to promote axonal outgrowth and plasticity; using spinal cord ES to activate or to increase the excitability of neuronal networks below the injury; using motor cortex ES to promote corticospinal tract axonal outgrowth and plasticity; and leveraging the timing of paired stimuli to produce plasticity. The review focuses on ES to enhance spinal circuit functions, the strength and efficacy of spared motor pathways, and the ultimately motor recovery after SCI. It addresses the mechanisms recruited and the neural target engaged by the stimulation.

• 1
  Spinal cord ES was initially explored to target axons that were damaged after SCI in order to bias the direction and possibly extent of neurite outgrowth, suggesting that spinal cord direct current ES creates a relatively static EF.
• 2
  The second distinct mechanism of action for ES following SCI is to increase the excitability of neuronal networks in the spinal cord or directly activate distinct neuronal motor pools.
• 3
  The third mechanism for ES after SCI is to increase intracellular signaling in stimulated neurons to upregulate axon growth-promoting factors and regeneration-associated genes in injured and spared neurons.