REM Sleep in Cats

Although the discovery of REM sleep ultimately had a huge impact on sleep research, the initial report of a connection between REM sleep and dreaming was met with "an outburst of apathy" in the scientific community (Lubin, 1974). Many psychologists were skeptical about any report involving a pop psychology topic like dreaming (pop psychology being a negative label for topics discussed in unscientific ways in popular magazines).


Only after REM sleep was demonstrated in animals, years later, did psychologists awaken to its significance. If REM sleep occurred in cats as well as humans, it must be real! William Dement's 1958 discovery of REM sleep in cats, plus similar work by French physiologist Michael Jouvet (zhu-VAY), really started the Golden Age of sleep research.

Why did Jouvet call REM sleep "paradoxical sleep"?

Jouvet was doing research on biological mechanisms of sleep in cats. When Dement published a report of REM sleep in cats, Jouvet realized he had seen the same thing. Jouvet called it paradoxical sleep. Jouvet chose the term "paradoxical" (which means strange or contradictory) because during this phase of sleep animals showed biological signs very similar to those of an awake animal. Breathing rates fluctuated, heart rates went up and down, and their eyes made quick, jerky movements beneath closed eyelids. Although their bodies seemed to be deeply relaxed, traces of activity appeared all over their bodies: there were tremors in the paws, quick scratching movements and rapid twitching of the whiskers. Their EEGs showed a noisy "alert" pattern.

Biological measurements from the animals in paradoxical (REM) sleep resembled those of awake animals, yet the cats were difficult to awaken from REM sleep. Despite the signs of activation such as twitching paws, the animals were never in an upright posture. When they went into this phase of sleep; they went completely limp, as if major muscles of the body were paralyzed. Jouvet wondered if the biological activity meant the animals were dreaming. If so, deep muscle relaxation might be necessary to prevent the animals from acting out their dreams.

What happened when Jouvet destroyed the locus coeruleus?

Jouvet found a brain area near a structure called the locus coeruleus that was necessary for muscle relaxation during REM sleep. When this area was surgically destroyed, the animals went to sleep normally, but during paradoxical or REM sleep they hissed and scratched violently, sometimes running around the cage with their eyes closed for a minute or two as if attacking another animal. Jouvet (1967) reported, "The sleeping animal's behavior may even be so fierce as to make the experimenter recoil." Evidently the cats were acting out dreams about their favorite daytime activity: hunting.

Jouvet's research implied that animals dream, just like humans. It also suggested that muscle relaxation below the neck during REM sleep prevented animals from acting out their dreams. The transition from non-REM to REM sleep can be observed in cats. In non-REM sleep, a cat's muscles are active, so it can sleep upright or in a sitting position as in the sketch below. An EEG taken while a cat slept in this position might show the typical large, slow waves of non-REM sleep.


By contrast, when a cat enters REM sleep, it loses all muscle tension below the neck and relaxes completely, as shown in the second picture. When a cat or other animal is limp like this, the EEG shows rapid, erratic activity characteristic of REM sleep. In dogs, cats, and rabbits (among other animals) one can observe external signs of dream activity such as paws and whiskers twitching during REM sleep. Mandy's paws were twitching when the picture was taken.


Relaxation of posture muscles can sometimes be observed in students. If a student goes to sleep during a lecture, the posture muscles retain their tension at first, so the student remains upright. In a few minutes the student may move into something resembling REM sleep. The muscles relax, and the student gradually keels over, striking the desk or a nearby classmate. The student usually wakes up confused, having been awakened in the middle of a dream.


What mammals have the most and least REM sleep? What is a possible explanation?

After Jouvet's research, other scientists looked for evidence of paradoxical or REM sleep in animals of other species. It turned out to be very common, especially among mammals. In fact, periods of REM or paradoxical sleep occur in all mammals except the spiny ant-eater, which is not a very typical mammal because it lays eggs. Among mammals, predators spend the most time in REM sleep. Allison and Cicchetti (1976) suggested that prey animals have less REM sleep because they need to wake up quickly if a predator finds them. Therefore they spend more time in the lighter stages of sleep.

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Copyright © 2007 Russ Dewey