In deep, or slow-wave, sleep, both cats and humans show slight muscle tension and low brain activity. But Dr. Jouvet found that during periods of REM sleep the muscles of cats were completely slack, even though their brain waves suggested physical activity. He called the REM state âparadoxical sleep,â since the brain is active even though the body is virtually still.
âDreaming became the third state of the brain, as different from sleep as sleep was from waking,â Dr. Jouvet wrote in âThe Paradox of Sleep: The Story of Dreaming,â published in France in 1993 and in English six years later.
He determined that a structure within the brainstem called the pons governed catsâ REM sleep. The pons is responsible for basic biological functions, like breathing and sensory perception; by contrast, the cortex, a higher brain region, governs conscious thought and actions.
Many researchers at the time assumed that since dreaming seemed to be a complex intellectual process, it would be centralized in the part of the brain responsible for reasoning. Dr. Jouvetâs discovery suggested that REM sleep could continue without the involvement of higher brain structures and that it had an important biological function even for animals with little capacity for reasoning.
Research has since confirmed that human beings have brain structures that govern REM sleep similar to those found in cats. Most warm-blooded animals, like mammals and birds, have periods of REM sleep. (Dolphins and many species of whales are notable exceptions.)
The question of whether animals dream was asked millenniums ago by Aristotle and has since occurred to virtually anyone who has watched a pet twitching in a deep sleep. Dr. Jouvet, who cautioned that there was no way for people to know for certain whether animals have…