Left vagus nerve stimulation suppresses experimentally induced pain

Objective: To test whether electric stimulation of the vagus nerve has an a ntinociceptive effect in humans. Background: In a variety of animal studies , vagus nerve stimulation was shown to inhibit nociceptive behavior as well as electric responses of spinal nociceptive neurons. In humans, chronic le ft vagus nerve stimulation is used to treat pharmacologically refractory ep ilepsy. Methods: The authors investigated experimental pain in 10 patients with seizures before and twice after implantation of a vagus nerve stimulat or by using different controlled stimuli, including noxious heat, tonic pre ssure, and short impact. Pain was quantified on a visual analogue scale. Tw elve nonepileptic age- and gender-matched individuals served as control sub jects. Results: Vagus nerve stimulation reduced increasing pain associated with trains of five consecutive stimuli at 1.5-second intervals ("wind-up"; p < 0.001). In a similar manner, pain on tonic pressure was reduced by vag us nerve stimulation (p < 0.03). Pain associated with single-impact stimuli as well as heat pain thresholds were unaltered under vagus nerve stimulati on. Thus, vagus nerve stimulation led to pain relief predominantly in exper imental procedures in which pain magnitude was amplified by central process ing. The antinociceptive effect was independent of the acute on-off cycles of vagus nerve stimulation. Conclusions: Vagus nerve stimulation is effecti ve in reducing pain in humans. In humans, the antinociceptive effect might rely on central inhibition rather than alterations of peripheral nociceptiv e mechanisms. These results indicate a promising, potential future role of vagus nerve stimulation in pain treatment.