This year, a study of 52 cardiac-arrest patients in Slovenia, published in the Journal of Critical Care, found that the 21% who had near-death experiences also had high blood levels of carbon dioxide, which has been associated with visions, bright lights and out-of-body experiences.

A study of seven dying patients at George Washington University Medical Center, published in the Journal of Palliative Medicine, noted that their brainwaves showed a spurt of electrical activity just before they were pronounced dead. Lead investigator Lakhmir Chawla, an intensive-care physician, notes that the activity started in one part of the brain and spread in a cascade and theorized that it could give patients vivid mental sensations.