During REM sleep some pretty bizarre stuff happens, if you look at the electrical activity of a brain that’s in REM sleep it almost exactly mimics the way the brain acts when it’s awake. The biggest difference being that the production of chemicals inside the brain like norepinephrine, serotonin, histamine is almost completely blocked and that causes the muscles to stop moving.
Which is why you can dream about flying, or running around, or fighting ninjas but your body doesn’t move. People who have a disorder achieving complete REM utopia move around in their sleep and act out their dreams. They can even get out of bed and sleep walk.
Oh before you move forward I should say two things. One, is that it’s possible to wake up and not be able to move your body because you’re still in REM atopia. You’re completely conscious and you now that you’re awake but your body’s not ready to move.
On the flip side you can also be inside a dream and know that you’re dreaming. This phenomenon is known as lucid dreaming and it’s particularly attractive because while I’m in a lucid dream I can make conscious decisions about what I do.
I can go fly to wherever I want or I can have tea part with Abraham Lincoln, I’m in control. But achieving a lucid dream is quite elusive. Howcast has a great video which I’v put in the description that gives some tips and tricks on how to achieve one.
Researchers were able to deprive mice of REM sleep by using this, inverted, inside a tub of water, way up to the tippy-top. Meaning that the mouse was only able to sit right on top of this little tiny surface.
The mouse can still fall into non-REM sleep but as soon as they reach REM sleep and their muscles relax they fall off the platform into the water, waking up. What they found was that when mice are not allowed to achieve REM sleep they have an incredible amount of trouble remembering things.
This happens in humans too. If you have people remember word pairs and then you don’t allow them to sleep, the next day their memory for that stuff is incredibly terrible.
But memory and REM does not stop there. If a person learns a difficult new task during the day, say a new instrument or a new type of difficult puzzle. You can measure the electrical activity in their brain while they do that. And then when they sleep that night, whether they know it or not, their brain replays those electronic impulses.
Many popular theories about why we dream are variations on the idea that while we sleep the unconscious part of our brain is busy organizing memories and strengthening the connections from the day before that we need in the future while getting rid of the junk that would otherwise clog the brain.