Effects of tDCS and VNS on Postoperative Analgesia

Two nonpharmacologic interventions have shown promise in treatment of chronic pain. Afferent Vagus nerve simulation (VNS) can modulate nociception, even though the exact mechanism is unclear. Clinically, it has found uses in chronic pain as well as early evidence of potential use in postoperative pain. Alternatively, transcranial direct current stimulation (tDCS) is a form of non-invasive and polarity-specific technique of modulating neuronal circuitry using a weak electric current delivered by a battery. tDCS has also been shown to modulate chronic pain and has been shown to produce EEG signatures similar to those seen in states of adequate intraoperative analgesia. This study seeks to evaluate the efficacy of tDCS and VNS in treating acute postoperative pain of patients in the post-anesthesia care unit after general surgery by randomizing 200 subjects in 4 groups: * Group +/+ will receive ten minutes of active tDCS followed by ten minutes of active VNS. * Group +/- will receive ten minutes of active tDCS followed by ten minutes of sham VNS. * Group -/+ will receive ten minutes of sham tDCS followed by ten minutes of active VNS. * Group -/- will receive ten minutes of sham tDCS followed by ten minutes of sham VNS. Patient's vital signs and pain level will be obtained before the procedure and after. Patients that have to stay in hospital will also be evaluated by opioid consumption and time from surgery to discharge.