Mysterious sleep

Originally published 19 September 1988

The title jumped off the new-book shelf at the col­lege library — a vol­ume called Why We Sleep.

Not the peren­ni­al­ly inter­est­ing ques­tion — Why Do We Sleep? — but the declar­a­tive promise of an answer — Why We Sleep. And the answer was promised with some author­i­ty; the vol­ume bore the imprint of Oxford Uni­ver­si­ty Press.

But the promise is a sham. By the third sen­tence of the book, British author/sleep researcher James Horne con­fess­es blunt­ly: “Of course, I do not have the answer to why we sleep, as too much is still unknown.”

So once again we are left in the dark. One-third of our lives is spent sleep­ing and no one knows why. Horne sums it up this way: “Despite 50 years of research, all we can con­clude about the func­tion of sleep is that it over­comes sleepi­ness, and the only reli­able find­ing from sleep depri­va­tion exper­i­ments is that sleep loss makes us sleepy.”

Two cen­turies ago Samuel John­son said the same thing in more som­no­lent lan­guage: “No searcher has yet found either the effi­cient or final cause [of sleep]; or can tell by what pow­er the mind and body are thus chained down in irre­sistible stu­pe­fac­tion; or what ben­e­fits the ani­mal receives from this alter­nate sus­pen­sion of its active powers.”

Watching and wondering

Pur­su­ing the mys­ter­ies of sleep, the moun­tain of sci­ence has labored might­i­ly and brought forth a mouse. Nay, not just a mouse, but thou­sands of mice, rats, pup­pies, chim­panzees, dol­phins, and drowsy under­grad­u­ates, all allowed to sleep or kept awake, and watched — watched by eager researchers keen to dis­cov­er why we sleep, to no avail.

There is no scarci­ty of the­o­ries: sleep restores the body; sleep restores the brain; sleep con­serves ener­gy; sleep occu­pies unpro­duc­tive time; sleep pass­es the scary hours of dark­ness; sleep is for dream­ing. No the­o­ry has yet found con­vinc­ing exper­i­men­tal sup­port. I asked the teenag­er at our house why teens sleep so much; he said “Ya don’t hav­ta think,” and that the­o­ry is prob­a­bly as good as any other.

Sleep research usu­al­ly takes one of two forms. In the first, the sleep­er’s brain waves, brain tem­per­a­ture, eye move­ments, and mus­cle tone (among oth­er func­tions) are mon­i­tored elec­tri­cal­ly. In the sec­ond, the sub­ject is deprived of sleep to see what happens.

The first line of research has demon­strat­ed that nor­mal sleep occurs in cycles and stages, usu­al­ly four cycles a night and at sev­er­al lev­els of obliv­ion defined by changes in the brain’s elec­tri­cal activ­i­ty. In each cycle there is an inter­val of sleep when the eyes twitch under closed lids, called REM (rapid eye move­ment) sleep.

Half-asleep dolphins

REM sleep is the dar­ling of sleep researchers, prob­a­bly because it accom­pa­nies dreams. But what is the brain doing in REM sleep? And why do we dream? Rats have REM sleep; do they dream too? Some dol­phins sleep with half of their brain at a time; does the sleep­ing half dream while the oth­er half is awake? The ques­tions are end­less, but answers are few.

Sleep depri­va­tion exper­i­ments have proved equal­ly unfruit­ful. Pity the poor rats forced to run on motor­ized tread­mills; if they nod off to sleep they tum­ble head over heels. One clas­sic piece of appa­ra­tus uses a rotat­ing pad­dle to push into water the hap­less rat that dares to doze.

Sleep deprived rats die with­in a week or two, but care­ful autop­sies have not made clear the cause of death. Maybe the lit­tle fel­lows die just to escape the rig­ors of the experiment.

Humans show no seri­ous impair­ments after a week of wake­ful­ness. A sev­en­teen-year-old school­boy named Randy Gard­ner set the record by stay­ing awake for 11 days; toward the end of the exper­i­ment he turned into a bit of a zom­bie, but quick­ly recov­ered after a long night’s sleep.

Lab shelves sag beneath vol­umes of data, yet no one has dis­cerned that sleep has any clear bio­log­i­cal func­tion. Then what evo­lu­tion­ary pres­sure select­ed this curi­ous behav­ior that forces us to spend a third of our lives uncon­scious? Sleep­ing ani­mals are more vul­ner­a­ble to pre­da­tion. They have less time to search for food, to eat, to find mates, to pro­cre­ate, to feed their young. As Vic­to­ri­an par­ents told their chil­dren, sleepy­heads fall behind — in life and evolution.

Uni­ver­si­ty of Chica­go sleep researcher Allan Rechtschaf­fen asks “How could nat­ur­al selec­tion with its irrev­o­ca­ble log­ic have ‘per­mit­ted’ the ani­mal king­dom to pay the price of sleep for no good rea­son?” Sleep is so appar­ent­ly mal­adap­tive that it is hard to under­stand why some oth­er con­di­tion did not evolve to sat­is­fy what­ev­er need it is that sleep satisfies.

Unless we have missed some­thing, says Rechtschaf­fen, sleep is the biggest mis­take evo­lu­tion ever made.

The break­through that will solve the rid­dle of sleep is yet to come. In the mean­time, we fall hap­pi­ly into bed at night to knit our rav­eled sleeves of care. The wor­ries of the day and ter­rors of the wake­ful night are relieved by the balm of sleep. Like the kid said, “Ya don’t hav­ta think.”