Big Question: Are near death experiences just hallucinations?

Curiosity contributor Susan Sherwood probed the latest research on the nature of near death experiences. Here is what she discovered.

A long tunnel. A bright light. Flashes of the past. These are common sensations described after near death experiences (NDEs). Three percent of Americans report having had NDEs -- many of them had come close to dying, while some were not actually in danger, though they believed they were [source: Choi]. Are NDEs brushes with the supernatural or misfiring neurons? Science has developed brain-based explanations for the experiences, but if it's all physiological, then why do so few people seem to remember them?

Perhaps the most well-known experience claimed during NDEs is that of moving through a tunnel toward a white light. Gliding towards an afterlife, perhaps? Scientists disagree: After all, oxygen deprivation -- common during grave illnesses and injuries -- can induce tunnel vision. Additionally, a study at the University of Maribor in Slovenia found that carbon dioxide levels in the blood were higher in heart attack victims who reported NDEs. Researchers found no other variables common to those patients.

Another dramatic report in some NDEs is the out-of-body phenomenon. Some people who have NDEs recall looking down from above and watching medical personnel work on their bodies. Although the patients were unconscious, some recalled sounds within the room and others remembered conversations that occurred in far-off parts of the hospital [source: Woodruff]. Is the soul exiting the body? Not according to a Swiss neuroscientist studying people with epilepsy. He found that when the temporoparietal junction (TPJ) in the brain was stimulated, research participants perceived out-of-body experiences. Since the TPJ is involved in perception, it may be that trauma causes a lack of blood to this part of the brain and induces hallucinations [source: Williams].

Many NDE patients describe seeing their life flash before them. Is it their day of reckoning or a reaction to hormones? Noradrenalin is released in the mid-brain during highly stressful situations, such as extreme fear or physical injury. This mid-brain section is affiliated with the brain areas that control emotion and memory; activation of the hormone might lead to expressions of memories in these parts of the brain [source: Choi].

Western NDEs may also include visions of deceased family and friends, feelings of euphoria and the awareness of being dead. NDEs are not always the same among cultures, however. Chinese NDEs suggest unpleasant out-of-body sensations, while Japanese NDEs replace the western "tunnel" with a cave -- indicating, perhaps, not only neurological but cultural reasons behind NDEs [source: Williams].