"Sometimes," said Walt Disney, "we can recognize ourselves in animals. That's what makes them so interesting." He was more right than he knew. One group of people may have had particular insight into human sleep behavior and its disorders: Disney animators.
It wasn't until the 1980s that "REM Sleep Behavior Disorder," or RBD, became formally recognized for human patients and it wasn't until 1990 that the International Classification of Sleep Disorders (ICSD) included it as an official diagnosis.
RBD is characterized, according to the ICSD, by "punching, kicking, leaping, and running from the bed during attempted dream enactment are frequent manifestations and usually correlate with the reported imagery." Typically, as we enter REM sleep, our bodies become paralyzed in order to prevent us from acting out out dreams. But in RBD, that paralysis doesn't occur.
Decades before RBD was taken seriously by the medical and scientific communities, Disney movies were full of scientifically accurate depictions of sleep and its disorders.
In 2007, a Spanish neurologist named Alex Iranzo was watching the 1950 animated feature Cinderella. In it, he noticed a cartoon dog, Bruno, having nightmares with dream enactment; that is, the pooch acted out his dreams while still asleep, rather than remaining paralyzed while dreaming, which is the typical, non-disordered way to dream. The dog's behavior, according to Iranzo, "strongly resembled RBD." The scene was not included in the original story by Perrault, nor in the Grimm adaptation, so it was likely the Disney writers themselves, Bill Peet and Ward Kimball, who were responsible for the astute observation of dog behavior.
His observation prompted Iranzo to team up with sleep researchers Carlos H. Schenck and Jorge Fonte to investigate the other animated Disney feature-length films and cartoon shorts. In addition to Bruno, they found at least three other cartoon dogs suffering from RBD.
In Lady and the Tramp (1955), it's Trusty who shows signs of RBD:
While dreaming of chasing a criminal through the swamps, Trusty has his eyes closed while growling, sniffing around, moving his paws as if he were running, and he drags himself across the floor. This episode was witnessed by Lady and Jock. In this same scene, Jock explains to Lady that Trusty is losing his sense of smell. During later scenes in the movie, the viewer becomes aware of how Trusty is also losing his memory. Thus, Trusty has developed the apparent clinical triad of RBD, hyposmia and cognitive impairment.
Indeed, it is now known that hyposmia (the loss of smell) often co-occurs with chronic, idiopathic RBD, and that the pair can be an early feature of neurodegenerative diseases like Parkinson's or dementia.
In The Fox and the Hound (1981), it's Amos Slade's dog Chief:
In one scene, Chief engages in an episode of presumed RBD that is witnessed by Tod and Copper. While asleep inside a barrel, Chief talks, howls, moans, moves the paws and the head, kicks and even laughs with his eyes closed. It is of interest to note that when the two friends are seeing Chief moving and talking, Copper believes that he is waking up, but Tod corrects him by observing that Chief is dream- ing that he is hunting a fox and a big old badger.
Unlike for Cinderella's Bruno, Chief's RBD-like symptoms were in the original novel by Daniel P. Mannix. "'The big half-bred bloodhound lay in his barrel kennel and dreamed he was deer hunting...The hound kicked convulsively in his barrel and whined with eagerness...With a cry that was half bark, half growl, the hound came awake.''
Finally, Pluto's Judgement Day was a 1935 short. Pluto himself experiences an episode of RBD:
Pluto has a nightmare in which he dreams that a judge and a jury totally composed of cats cast judgment on him for having chased and tormented cats throughout his life. He is found guilty and is condemned to die by burning at the stake. When in the dream the flames of death are encircling him, Pluto is shown to actually be asleep while howling, barking and moving all four paws vigorously, and then he runs away with his eyes closed until he falls into a washing tub filled with water and suddenly awakens, happily realizing that he was only having a nightmare.
What's impressive about this is that each of these cartoons were produced before RBD was formally described in humans, let alone in dogs. (Though the 1981 feature The Fox and the Hound came after first French researchers Jouvet and Delorme described RBD in an experimental cat model, in 1965.)
Was the Disney animation studio secretly full of sleep scientists? Probably not.
What inspired the screenwriters for Disney to include episodes of (dog) RBD remains speculative. However, a likely possibility is first-hand experience in witnessing RBD in their own or others' dogs or they may have devised an exaggerated form and caricature of the facial twitching, padding movements and whining sounds that are commonly seen in normal dogs while they sleep
Still, the writers' perceptions of their own and their pets' sleep behaviors is remarkably consistent with the medical and psychological literature. The portrayals of RBD in Bruno, Trusty, Chief, and Pluto are similar among themselves and also are common with human RBD. For example, all the dogs are older males, and RBD is also more common in older human males.
They say that storytellers are among the most astute observers of human behavior; those employed by Disney in the so-called "golden age of animation" certainly were.
Read the entire study online at Sleep Medicine.