Naps for Better Recall

NEWS SCAN32 SC I EN T I F I C AM ER I C A NM ay 2 0 0 8If during that soporific hou r after lunch, you succumb to the temp -tation of a quick nap, you are liable to earn your b oss's d ispleasure. Bu t judging by the latest results from sleep research, you should be getting a pat on the back.Mou ntains of evidence reveal that sleep enh ances memory. Now Olaf Lah l o f th e Univers ity o f Duss eldo rf in G ermany an d h is colleagues have stru ck a blow for power-n appin g by show ing that falli ng asleep for on ly s ix minu tes is enough to signifi cantly en hance memory. Th is is the shortest period of sleep found to affect mental functioning. It su ggests, Lahl says, that someth ing happens at the point of losing consciou sness that solidi-fies memories.The subjects in L ah l's stu dy rep orted to the university's sleep lab at 1 P.M.They were given two minutes to memorize a list of 30 words and tested on their recall an hou r later. In the
interi m, th ey either stayed awake, took a six-minute n ap or a longer sno oze averaging 35 minutes. On no sleep, subjects recalled an average of just under seven words. A short nap raised per formance to more than eight. A longer nap, includ ing some time in deeper sleep, boosted recall to more than nine words.Lahl previously thought the benefits of sleep for memor y were mainly pas sive—that un co nscious ness slows th e rate at which new ex perience erodes old memo -ries but that the sleeping brain do es noth -ing special to help s tore wak ing exp eri-ence. But this latest finding, appearing in the Journ al of Sleep Research, has changed h is mind , b ecause six minutes do es not seem long enough to forget much.Bu t sleep r esearc her Jim Horn e o f Loughborough Un iversity in England sus -pects that you need deep sleep to get a mem-ory benefit and that the nappers might just have been a bit fresher than their continu-ously awake counterparts. In
Lahl's study, he says, "it's more likely sleepiness is im-pairing memory than sleep enhancing it."Robert Stickgold, who stud ies sleep at Harvard Medical School, disagrees. "It's hard to believe that six minutes' sleep could make you les s sleepy," he says. Instead Stickgold suspects that the ex periment re-veals a process of memory con solidation that begins even before sleep and that could continue after wak ing from a very br ief sleep. "In the last couple of minutes of wak-ing, the brain could be putting stickers on topics for later processing," he speculates.A sleeping brain is not merely on stand-by; it r uns through a suite of complex and orderly activities. One of these is a .ow of n eu ral activity fro m the h ip pocampus , where shor t-term memories are formed, to the cortex, where they are stored in more du rable for ms—a po ssible r eas on p eo ple can re memb er th ings better on awakening. Nor is this pro cess simply a matter of
s crib ing data into neu ral tissue. Several recent studies of sleep and sleeplessness show that slumber is es pecially impor tant fo r do ing clever stuff with information , such as ex tracting the gist of what has been learned , combining facts in interesting ways and dealing with the day's emotions."Executive thinking is par ticu larly im-paired by sleep loss," Horne says. "You be-come much more blinkered in your thin k-ing, less able to deal with novelty and less able to evaluate risk." This is bad news for medics, shift workers and military com-mand ers, he o bserves, and p erhaps ex-plains why casinos stay open all night."The most impor tant processing of in-formation during sleep is to add mean ing to information and fit it into a larger con-text," Stickgold explains, adding that such processing seems most likely to have driven sleep's evolution. "Of all the functions of sleep, memory is the only one that explains why you'd have to go
through the danger-ous phenomenon of losing consciousness, as opposed to having quiet rest."Lah l, in contrast, think s that sleep is primarily about repairing and detoxifying the brain—h e points out that there is no cor relation between how much you learn in a day and how much you need to sleep at n ight. Never theless, he is now looking for an effect of two-minute naps. "We're trying to put it at the extreme, to find the critical period of time where memor y en-hancement might happen . Bu t in such short periods it's difficult to decide if the subject is asleep."John Whitfi eld is based in Lon don.SLEEPNaps for Better RecallEven a six-minute snooze boosts me moryB Y J O HN W H I T FI E L DNapping Is NaturalUntil rece ntly, sle ep researche rs ove r-looked naps, perhaps be cause their soci-etie s frown on afte rnoon snoozes. But short sle eps are the norm in animals, says psychologist Olaf Lahl of the University of Dusse ldorf in Ge rmany.
"Getting all your sle ep in a monolithic block is quite unusu-al," he adds. And pe ople with loose r sche dule s—infants and the elderly—are much more like ly to nap, he notes.YOU SNOOZE , YOU DON'T LOSE : In fact, you stand to gain, in te rms of an improved short-term memory.c 2008 S C IEN T IFIC AM E RIC AN , IN C .

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