Vagus Nerve Stimulation for Neuromodulation: Evolution from Bench to Bedside.

Background/Objectives: Vagus nerve stimulation (VNS) has evolved from a laboratory experiment to a standard of care in several neurological disorders like epilepsy, depression and stroke rehabilitation at present. Methods: We reviewed the published literature relevant to its origins in animal models leading to various clinical applications. Results: Bailey and Bremer published their observations following VNS in animals while further studies established its utility in some forms of epilepsy. Subsequent observations in epilepsy patients treated with VNS revealed the unequivocal improvement in psychological and behavioral disorders. Consequently, VNS received approval for its application in resistant depression disorders. Multiple studies revealed changes due to neuronal plasticity following VNS that could result in the significant clinical recovery of motor function in chronic ischemic stroke patients. Chronic incomplete cervical spinal cord injury, head injury and peripheral nerve injury deficits are also being studied for recovery patterns. Transcutaneous approaches and closed-loop stimulation are showing encouraging results that may facilitate the extension of the application of neuromodulation using VNS. Conclusions: For the recovery of motor function following paralysis in stroke patients or cervical spinal cord injuries, the timing of the stimulation after physical activity during rehabilitation has been identified as a key factor. In addition to the timing of the stimulation, the titration of the parameters is also being studied to obtain optimized recovery in cases of motor, sensory, or sphincter deficits.