One in three people feels genuine, physical discomfort when he or she sees another person in pain. Researchers at the University of Birmingham in the United Kingdom found that when they showed a video of an athlete being injured, most people in the study had a sympathetic emotional reaction. However, one third of the participants actually felt pain in their bodies corresponding to the part injured in the video.

The hypersensitive participants repeated the study while undergoing MRI scans. Researchers discovered that the part of the brain that handles pain exhibited greater activity when the injury video was shown (Richard Alleyne, "Some People Really Feel Your Pain," The Daily Telegraph, Dec. 22, 2009).