Is it simply a dream?

A near-death experience -- surviving a car crash, a near drowning or a cardiac arrest and living to tell about it -- can be transforming for some people. Their recollections often involve intense light, a feeling of peace or of being on the threshold of another world, the defining elements of a near-death experience.

Now, in a study in the April 11 journal Neurology, researchers have found common ground between those experiences and flukes in the brain’s sleep-wake control system.

Dr. Kevin Nelson, neurophysiologist at the University of Kentucky, questioned 55 people who were sure they had been dead and compared them with 55 people without such experiences.

Of the people he studied who had near-death experiences, 60% reported having had a condition called REM intrusion at times in their lives, whereas among the people who did not have near-death experiences, only 24% had had REM intrusion.

In this condition, the boundaries between sleep and wakefulness are blurred. The most extreme version of REM intrusion is narcolepsy, or a sudden, uncontrollable need to sleep. But some people merely feel, for example, an inability to move for a short time during waking hours. A feeling like that, during a crisis, can convince people they were dead, says Nelson.

And the light? That, he says, could be part of the visual acuity that occurs during REM.