Experiment Overview Healthy men and women are actively being recruited for this randomized, controlled, double-blind study that requires 3 separate visits: 1 screening visit, and 2 subsequent visits for the experimental sessions. In a within-subject, cross-over design, the response to experimentally induced heat pain is examined before, during, and after transcutaneous (non-invasive) vagus nerve stimulation (via a region of the ear exclusively innervated by the vagus nerve) compared to stimulation of the earlobe (control site; innervated by cervical spinal nerves). The following data are collected before, during, and after experimental and control stimulation of the left external ear: warm sensation and heat pain thresholds, and ratings of mood, pain intensity and unpleasantness after short and long duration heat pain stimuli. Autonomic measures (heart rate, respiration, blood pressure, and skin conductance) are also collected throughout the study session. This study will allow us to address the following questions: 1. Does the experimental condition (vagus stimulation) compared to the control condition (earlobe stimulation) significantly decrease pain perception? 2. Does the experimental condition, compared to control, significantly improve mood? 3. Does mood mediate the effects of vagus stimulation on pain perception? In addition, we will determine whether vagus stimulation, compared to control, increases heart rate variability.
