Why do we sleep?
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Posted by Fotopoulou Sophia in Science section |
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After five decades of research, even the most gifted scientist on the planet, cannot explain why people sleep.
"It may be the biggest open question in biology,” said Dr. Allan Rechtschaffen, a sleep expert and a professor emeritus at University of Chicago.
The researchers who bragged, at a conference in the early 1970’s, that the secret of sleep would be theirs by the millennium have had to revise their estimates.
“We were to optimistic,” said Dr. Michel Jouvet a professor emeritus at Claude Bernard University in Lyon, France, and a member of the French Academy of Sciences who attended that long ago meeting. “The brain is more complicated than we thought.”
The discovery of rapid eye movement, or REM, sleep in 1953 awakened scientists to the realization that sleep was not “a simple turning off of the brain,” but an active, organized physiological process, said Dr. Jerome Siegel, a professor of psychiatry and biobehavioral sciences at the University of California at Los Angeles.
Five decades later, few researchers would dispute that sleep serves some critical, if unknown, biological purpose.
All mammals, birds and reptiles engage in some form of sleep, Dr. Rechtschaffen noted in a 1998 paper. Sleep has also endured through the eons, despite the fact that it interferes with other survival enhancing activities.
“While we sleep, we do not procreate, protect or nurture the young, gather food, earn money, write papers, etc,” Dr. Rechtschaffen wrote.
Equally telling is the finding that when humans and other animals lose sleep, they proceed to make it up, paying off the “debt” by sleeping longer or more intensely.
Sleep deprivation over long periods appears to have serious consequences, though what they are is still debated, because it is difficult to separate the effects of lost sleep from those of stressor other factors.
Researchers once thought that prolonged lack of sleep produced mental illness. They now know that this is not the case, though waking subjects up every few minutes, early studies showed, made them cranky. Nor is there proof that humans have died from a lack of sleep. But rats deprived of sleep die in two to three weeks, or in five to six weeks if they are deprived only of REM, a sleep stage in which brain activity is similar to that in waking. Whether the rats die from massive heat loss, infection, or other cause is unclear.
What is it about sleep that makes it essential to life? Experts say that it is not simply the fact that humans and other animals need rest. “You can rest all you like and you still need sleep,” Dr. Rechtschaffen said. Another theory holds that sleep may serve to protect animals, by taking them out of circulation during the dangerous hours when predators roam. Yet this theory, Dr. Rechtschaffen and others point out, cannot explain why the amount of sleep lost one night is made up the next or why the impact of long-term sleep deprivation is so severe.
Smaller animals, studies have found, sleep longer than large ones: a horse snoozes for 3 hours a day, a ferret close to 15. The fact that an animal’s metabolic rate slows with size has led to yet another hypothesis about sleep’s purpose: that it may act to repair cell damage caused by free radicals, chemicals released during the metabolic process.
The most promising theory so far, some experts believe, proposes that REM sleep plays a role in brain development. Newborns spend more time in REM than adults. Animals that spend long periods in REM are also more immature at birth.
In the meantime, the search continues: “There is something tremendous out there, and we just haven’t found it.”
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