Quote Originally Posted by moonshine View Post
That seems a bit woolly to me thor. That theory would apply only if NREM and REM dreams were similar.

For what I've read they are not. NREM dreams have clearly been described, by scientists, as thoughtlike or daydreaming.
Which in my mind is a more credible reason for not needing SP during NREM sleep.
REM dreams are generally more vivid, and NREM dreams are generally more thoughtlike, so if you have a vivid dream it's most likely a REM dream, and if you have a thoughtlike dream it's most likely an NREM dream. However, a significant proportion of REM dreams are thoughtlike, and a significant proportion of NREM dreams are vivid. Yet, people do not act out vivid NREM dreams. (Well, they do in sleepwalking and night terrors, but those are anomalous anyway.)

I think asking why we have atonia only in REM sleep is the wrong question. In my opinion a more interesting question is: what is it about REM sleep that causes the brain to transmit nerve impulses to make the limbs move, thereby necessiating REM atonia?

As an aside, I don't understand why you say "thoughtlike or daydreaming", because daydreaming is very immersive and quite the oppsite of thoughtlike.