This study is designed to test a specific hypothesis exploring the neurophysiologic mechanism(s) that underlie the pain- relieving effects of immersive Virtual Reality (VR) as a non-pharmacologic pain management technique, using healthy volunteers experiencing carefully controlled thermal and/or electrical pain in the laboratory. Over the past decade, our research group has performed a series of NIH-funded investigations of VR analgesia - in both the clinical pain and laboratory pain settings - demonstrating its clinical efficacy and safety. In the current study we will test pharmacologic manipulation of VR analgesia (with the opioid analgesia antagonist naloxone). We anticipate that this theoretical work will provide a foundation for future clinical applications of immersive VR - whether used alone or in combination with other analgesic agents - and make immersive VR a more effective and more widely used analgesic tool for the treatment of clinical pain.