Kevin Nelson is a neurologist at the University of Kentucky. A book by Nelson has just been published in the USA by Dutton, reports an article in the 25 December 2010/1 January 2011 edition of the "New Scientist" magazine (pp 80-81.) It is titled "The Spiritual Doorway in the Brain."
Nelson suggests that there are three states of consciousness, these being "awake"; "non-REM sleep" and "REM sleep." These three distinct states can blend at times.
Regarding NDEs he says "What I have discovered is that the switch in the brain stem that regulates these three states functions differently in people who have NDEs. These people are more likely to get stuck between the REM state and waking. So it looks like some people are prone to having these kinds of experiences. Interestingly, it tends to run in families."
On OBEs during NDEs.
"These come about because the temporoparietal region of the brain is turned off, so the brain is no longer able to map the body's position in space. "
"REM consciousness turns the temporoparietal region off, so if you are semi-conscious in a borderland between waking and REM, you can easily have an out-of-body experience."
Brainwave measurements show that lucid dreaming is a conscious state between REM and awakening. During REM consciousness, the dorso-lateral prefrontal cortex is turned off. As that's the executive rational part of the brain, this explains why dreams are so bizarre. But if the dorso-lateral cortex turns on inside a dream, you become aware you are dreaming."
Very interesting material. I look forward to reading the book.
Naturally, one also thinks of the possible relevance to alien abduction accounts. I'll ponder this question for a while.
For more on Nelson's work, click on http://www.skeptiko.com/kevin-nelson-skeptical-of-near-death-experience-accounts/