Dreams, memory, and thermoregulation
After studying dozens of subjects, including his son and Dr. Kleitman’s daughter, and using miles of polygraph paper, the two scientists published their findings in September 1953 in the journal Science. Dr. Kleitman didn’t expect the discovery to be particularly earth-shattering. When asked in a later interview how much research and excitement he thought the paper would generate, he replied: “none whatsoever.” That’s not how things went, though. “They completely changed the way people think,” Dr. Blumberg said. Once and for all, the REM discovery put to rest the idea that sleep was a passive state where nothing interesting happens.
Dr. Aserinsky soon left the University of Chicago, while Dr. Kleitman continued research on rapid eye movements in sleep with his new student, William Dement, MD. Together, they published studies suggesting that REM periods were when dreaming occurred – they reported that people who were awakened during REM sleep were far more likely to recall dreams than were those awakened outside of that period. “REM sleep = dreams” became established dogma for decades, even though first reports of dreams during non-REM sleep came as early as Dr. Kleitman’s and Dr. Dement’s original research (they assumed these were recollections from the preceding REM episodes).
“It turns out that you can have a perfectly good dream when you haven’t had a previous REM sleep period,” said Jerome Siegel, PhD, professor of psychiatry and biobehavioral sciences at UCLA’s Center for Sleep Research, pointing out that equating REM sleep with dreams is still “a common misconception.”
By the 1960s, REM sleep seemed to be well defined as the combination of rapid eye movement with EEG showing brain activation, first noted by Dr. Aserinsky, as well as muscle atonia – a state of near-total muscle relaxation or paralysis. Today, however, Dr. Blumberg said, things are considerably less clear cut. In one recent paper, Dr. Blumberg and his colleagues went as far as to question whether REM sleep is even “a thing.” REM sleep is prevalent across terrestrial vertebrates, but they found that it is also highly nuanced, messing up old definitions.
Take the platypus, for example, the animal with the most REM sleep (as far as we know): They have rapid eye movements and their bills twitch during REM (stillness punctuated by sudden twitches is typical of that period of sleep), but they don’t have the classic brain activation on EEG. Owls have EEG activation and twitching, but no rapid eye movements, since their eyes are largely immobile. Geese, meanwhile, are missing muscle atonia – that’s why they can sleep standing. And new studies are still coming in, showing, for instance, that even jumping spiders may have REM sleep, complete with jerky eye movements and limb twitching.
For Dr. Siegel, the findings on REM sleep in animals point to the potential explanation of what that bizarre stage of sleep may be all about: thermoregulation. “When you look at differences in sleep among the groups of warm-blooded animals, the correlation is almost perfect, and inverse. The colder they are, the more REM sleep they get,” Dr. Siegel said. During REM sleep, body thermoregulation is basically suspended, and so, as Dr. Siegel argued in The Lancet Neurology last fall, REM sleep could be a vital player in managing our brain’s temperature and metabolic activity during sleep.
Wallace B. Mendelson, MD, professor emeritus of psychiatry at the University of Chicago, said it’s likely, however, that REM sleep has more than one function. “There is no reason why one single theory has to be an answer. Most important physiological functions have multiple functions,” he said. The ideas are many, including that REM sleep helps consolidate our memories and plays an important role in emotion regulation But it’s not that simple. A Swiss study of nearly 1,000 healthy participants did not show any correlation between sleep stage and memory consolidation. Sleep disruption of any stage can prevent memory consolidation and quiet wakefulness with closed eyes can be as effective as sleep for memory recall.
In 1971, researchers from the National Institute of Mental Health published results of their study on total suppression of REM sleep. For as long as 40 days, they administered the monoamine oxidase inhibitor (MAOI) phenelzine, a type of drug that can completely eliminate REM sleep, to six patients with anxiety and depression. They showed that suppression of REM sleep could improve symptoms of depression, seemingly without impairing the patients’ cognitive function. Modern antidepressants, too, can greatly diminish REM sleep, Dr. Siegel said. “I’m not aware that there is any dramatic downside in having REM sleep reduced,” he said.
So do we even need REM sleep for optimal performance? Dr. Siegel said that there is a lot of exaggeration about how great REM sleep is for our health. “People just indulge their imaginations,” he said.
Dr. Blumberg pointed out that, in general, as long as you get enough sleep in the first place, you will get enough REM. “You can’t control the amount of REM sleep you have,” he explained.