Why do strong emotions often trigger sensations in our chests and abdomens? Scientific American says researchers don't know for sure yet, but new findings point to a physical connection between areas of the brain linked to emotional and physical pain:
According to a 2009 study from the University of Arizona and the University of Maryland, activity in a brain region that regulates emotional reactions called the anterior cingulate cortex helps to explain how an emotional insult can trigger a biological cascade. During a particularly stressful experience, the anterior cingulate cortex may respond by increasing the activity of the vagus nerve—the nerve that starts in the brain stem and connects to the neck, chest and abdomen. When the vagus nerve is overstimulated, it can cause pain and nausea.
More interesting still, Scientific American writes that empathy can also affect pain perception. A 2006 paper reportedly detailed how a mouse's sensitivity to pain increases when it "observes its cage mate in agony" yet decreases when near another unharmed mouse. A subsequent study based on magnetic resonance imaging data identified similar response in humans (minus the cage mate in agony part, that is).