The next time you wake up after a good night's sleep. you might want to give your brain a rest. Researchers at Harvard Medical School have found that during certain phases of the human sleep cycle, the mind is more active than it is during waking hours.

Harvard Professor of Psychiatry J. Allan Hobson believes that the Rapid Eye Movement (REM) sleep stage, during which a person's eyes move quickly back and forth, is the most energetic phase of our sleeping unconsciousness. During that period, the body restores its metabolic order through the process of dreaming, which is now believed to be responsibile for more than just expressing our Freudian desires, according to Hobson.

"The interesting thing was that before, nobody had known that the brain was always active. People couldn't figure out where dreams came from--were they angels or signs from the supernatural? No one knew. People in the nineteenth century thought they came from the outside or from something like your stomach. What we found out was that the brain itself was causing dreaming, sending signals to itself."

Electrodes

To detect brain activity during REM sleep in his laboratory at the Massachusetts Mental Health Center, Hobson uses electroencephalograms (EEG). He says measurements of the brain's electrical output, made by attaching electrodes to the head, show that the brain is almost 90 percent more active during REM sleep than at any other slumber time. The normal human passes through five distinct stages of sleep, with the REM stage following the lighter, first two stages. Sleep stages three and four--following REM chronologically--are deep sleep periods.

"What we took was essentially a novel approach to dream research," says Hobson, who received an M.D. from Harvard in 1959. "Nobody had ever studied the electrical activity of the individual [brain] cells during sleep. What we did was use microelectrodes in the brain to see what was going on. We put them under the bone and aimed them at the cells where we thought REM was occuring and put an object on the bone to measuere the output."

Hobson, who first carried out his electrode experiments in 1977, says these initial studies led to impressive results. "We began to map activity of the cells during sleep and came up with a now much discussed model."

Neuron Model

Hobson and his colleague, Robert McCarley, say they found the brain appears to contain two populations of neurons, which are cells specialized for transmitting sensory information, and each type of neuron interacts with the sleep process in different ways.

"We learned that some neural cells had a preference for being 'on' [processing hormones] during awake time, and some were always 'on' during sleep. But some of the 'awake' cells turn 'on' while in REM sleep," he says.

"What we began to notice was that there was an [activation of some of the] neurons during sleep, perhaps causing REM," he says.

Hobson says his dual neuron dream model allows him and his research staff to study "dreaming as a state as opposed to dreaming as a story." Hobson's concept allowed the researchers to study the content of dreams not as Sigmund Freud would have psychoanalyzed them, but as physiological processes.

Hobson and McCarley, who are both associated with the Department of Psychiatry at the Medical School, also tried to add to their dream model by analyzing the chemicals processed in the brain during REM sleep and then studying differences in the way various hormones direct sleeping versus waking activities.

The researchers found that there were drastic chemical differences between a sleeping and a waking brain. When a person is not asleep, one of the two groups of neurons in Hobson's model, called aminergic neurons, processes the hormones norepinephrine and seretonin, which can control bodily functions. On the other hand, if someone is engaged in REM sleep, the other set of neurons, referred to as cholinergic, become receptive to the hormone acetylcholine for muscle control.

Hobson recently performed several other experiments to elucidate other details of his model, hoping to find a way to induce REM sleep in animals. "We wanted to test the 'on' [cholinergic] cells to see if giving them acetylcholine stimulated REM sleep," says Hobson. "This gave us experimental control of REM. We could induce dreaming in animals, and instead of having to wait 30 minutes before REM onset, we could induce it in two or four."