What happens when we dream?

Dr. Garfield: When we dream, our central nervous system is going into an active state, which it is does periodically during our sleep. Nobody is quite sure why, by the way. Is it a testing of the system to see if everything's still working? We don't quite know.

Physiological changes occur periodically during sleep so that our heart rate goes up somewhat, our breathing gets more rapid, our temperature slightly increases, our brain waves change. And although our large muscles are inhibited, so that we don't start acting out our dreams, the small muscles around our mouth, our fingers and our eyes twitch back and forth accompanying the central nervous system arousal.

There's a sexual arousal as well — this is a part of the whole system. So the idea of dreams having a sexual component is literally true. That is, men experience erection and women become more lubricated, but this is just one aspect of what is happening physically in dreaming.

I describe dreaming as a three-story house. On the basement level you've got the physical changes going on in the body, and then, on the main floor of the house, you've got these visual images, sounds, and sometimes smells and all the other physical experiences we have in dreams that are expressive of our emotional state, how we are psychologically at the moment.

At another level, kind of the attic, there are sometimes experiences that we can't explain in which people connect with on another level of themselves, whether it's the spiritual or creative, or extrasensory. We don't know how this happens, but sometimes people have very unusual experiences in dreams, for example, a dream where someone to whom they're emotionally close comes to say goodbye and that they love them and that that they will always be watching for them and the person wakes up and a few hours later learns that person has died at the time of the dream. And these are very powerful experiences for the dreamer that we can't explain in a scientifically acceptable manner.

All of these experiences are there when we dream: the physical changes in our bodies, the psychological expression of how we're feeling emotionally at the time of the dream, and this other world that we sometimes seem to touch in dreams.