Dr. Matthew Walker

When I wake you up out of tonic REM sleep, when the eyes aren't moving, I'm around that 80% probability.

If I wake you up out of REM sleep when your eyes are darting back and forth, there is 95% to 100% probability that you're going to report a dream.

Some people, theories in the past have said, well, if that's the case, then presumably those eye movements are tracking something in the dream.

If you do careful analyses, that just does not seem to hold up.

There is some evidence that that may be the case, but your eyes are moving back and forth.

It seems that these are...

impulses that are going to your eyes that don't have a strong correlation with what it is that you're dreaming visually in the scene.

That's not the case.

But that's a little bit of a definition of what dreaming is and also when dreaming occurs.

I should probably note, by the way, that we human beings, we seem to be special in our REM sleep dreaming amounts.

Now, I've just done a little bit of a sleight of hand.

When I say REM sleep, I'm going to infer that it's dreaming.

Charles Nunn, wonderful scientist, has looked at the proportion of REM sleep across different mammals.

And what he found was that we human beings are a complete anomaly when it comes to our relative amounts of REM sleep.

In other words, our dream sleep.

He found that across most other primates,

REM sleep was usually averaging about 9% of the sleep period.

However, we human beings, on average, including when we're young, will have a REM sleep proportion of about 20%.

So if you plot the amount of REM sleep of primates

in a graph, they're all sort of clustered around this mean.