Any­one who knows me knows that my favorite pas­time is nap­ping. In Col­lege, I would come back to my dorm room, and like clock­work, would take a nap. My best friend in Eng­land, who got quite a kick out of my pas­sion for nap­ping, once tried to per­suade me to drink a cup of tea after lunch instead of tak­ing my cus­tom­ary nap. I really tried, but I soon gave in to my nap crav­ings. Some­times I feel like I really need to re-charge my brain batteries.

Well, now sci­ence is on my side. I just love this new study, which was pre­sented by Matthew Walker, assis­tant pro­fes­sor at UC Berke­ley, at the annual meet­ing of the Amer­i­can Asso­ci­a­tion of the Advance­ment of Sci­ence (AAAS) con­fer­ence in San Diego this past Sun­day (Feb. 2010).

Walker and his col­leagues Bryce A. Man­der and Sangeetha San­thanam split up a batch of 39 healthy young adults into two groups. One group napped, the other did not.

At noon, both groups took a learn­ing task thought to recruit the hip­pocam­pus. The hip­pocam­pus is a region of the brain known to play an impor­tant role in the for­ma­tion of new mem­o­ries. Over the past few years, var­i­ous researchers have found that fact-based mem­o­ries are tem­porar­ily stored in the hip­pocam­pus before other regions of the brain can oper­ate on the con­tent, espe­cially the regions of the brain respon­si­ble for higher-order rea­son­ing and think­ing.  At this point in the exper­i­ment, both groups showed sim­i­lar lev­els of performance.

Then, at 2pm, the nap group took a 90-minute nap while the no-nap group stayed awake, pre­sum­ably watch­ing the nap group enjoy­ing their nap. After nap-time both groups then took more learn­ing tests. The nap­pers did bet­ter on the tasks than those who stayed awake, demon­strat­ing their higher capac­ity to learn.

The researchers inter­pret these find­ings as sup­port­ing their hypoth­e­sis that a major func­tion of sleep is to clear away all the clut­ter stored in the hip­pocam­pus to make room for new infor­ma­tion. In the words of Walker:

“It’s as though the e-mail inbox in your hip­pocam­pus is full and, until you sleep and clear out those fact e-mails, you’re not going to receive any more mail. It’s just going to bounce until you sleep and move it into another folder.”

Walker also likens the brain to a sponge:

“Sleep is crit­i­cal for learn­ing. It’s like the brain is a sponge. Sleep wrings cer­tain key regions out so you’re able to soak up new infor­ma­tion the next day.”

Short mid-day naps may be good because they get you into a par­tic­u­larly ben­e­fi­cial part of the sleep cycle. EEG stud­ies (that mea­sure the elec­tri­cal activ­ity of the brain) have shown that this memory-refreshing process occurs dur­ing Stage 2 non-REM sleep. We actu­ally spend at least 50% of our sleep­ing time in this stage, sug­gest­ing an adap­tive pur­pose for this stage of sleep:

“I can’t imag­ine Mother Nature would have us spend 50 per­cent of the night going from one sleep stage to another for no rea­son. Sleep is sophis­ti­cated. It acts locally to give us what we need,” says Walker.

Now, what about that cup of tea? Was my friend in Eng­land right? His advice is usu­ally spot-on, but this time he may have been mis­guided.  Sara Med­nick at the UC San Diego (and author of the book: Take a Nap! Change Your Life) divided her sub­jects into two groups: one group received 200 mg of caf­feine and did not nap and the other group just took a nap. Then both groups under­went a bat­tery of tasks, includ­ing mea­sures of typ­ing, and mea­sures of mem­ory recall, tap­ping into visual, ver­bal, and motor mem­ory. She found that the day nap­pers did bet­ter on all the tasks than those who popped the caf­feiene pill. “Of course, that’s bad news for Star­bucks,” says Med­nick. Med­nick also notes: “Which would you rather be: wired or smart?”

Med­nick points out that the time dur­ing the day a per­son should nap varies depend­ing on the person’s age. She says that since teenagers and young adults have a slightly shifted sleep cycle, going to bed late and wak­ing up early, their ideal nap­ping win­dow is in the after­noon, around 4p.m. The ideal nap­ping win­dow for adults, in con­trast, is between 1 to 3 p.m., since adults usu­ally sleep between 11 p.m. and mid­night and wake up between 6.am. and 8 am.

Walker and his col­leagues are also inter­ested in the link between age and the func­tion of sleep. They are now inves­ti­gat­ing whether the reduc­tion of sleep as we age is asso­ci­ated with the well-replicated decrease in our abil­ity to learn as we age. As noted in the offi­cial UC Berke­ley Uni­ver­sity press release, this is fas­ci­nat­ing research and could greatly improve our under­stand­ing of neu­rode­gen­er­a­tive con­di­tions such as Alzheimer’s disease.

Sleep­ing is Good for You

The Walker and col­leagues study is one among a num­ber that show that sleep, more gen­er­ally, can be very ben­e­fi­cial for a wide range of pos­i­tive out­comes. At UC Berke­ley, both Walker’s research group and Alli­son Harvey’s group at the Sleep and Psy­cho­log­i­cal Dis­or­der Lab­o­ra­tory have found that get­ting a good amount of sleep at night is tied to a bet­ter immune sys­tem, meta­bolic con­trol, mem­ory, learn­ing, and emo­tional func­tion­ing. Most of us are famil­iar with the often cited find­ing that pulling an all-nighter the night before an exam can decrease the abil­ity to remem­ber the infor­ma­tion by roughly 40 per­cent, but it’s really cool to see all these other ben­e­fits of sleep.

I can relate. Some­times when I am learn­ing a new tune on my piano, I get frus­trated in the moment when I think I am no longer mak­ing progress. Some­times when I try to tackle the song the next day after a good night’s sleep, I real­ize I have learnt the whole thing the night before! In fact, research does show that peo­ple have 20 to 30 per­cent bet­ter recall of what they learned dur­ing a piano les­son if they are tested after a full eight hours of sleep than if they are tested right after the piano lesson.

There are also ben­e­fits of sleep for cre­ativ­ity. Mul­ti­ple threads of research sup­port this notion, and the link between sleep­ing and cre­ativ­ity has been noted by promi­nent researchers such as Jerome Singer as well as Walker:

“This starts to sound a lot like the basis for human cre­ativ­ity. The fus­ing of things that don’t seem to have any con­nec­tion. That’s what sleep, par­tic­u­larly dream­ing does. Like good cook­ing, when it comes to mem­ory, it’s not enough to chop up the ingre­di­ents and put them together. The brain needs time to let things marinate.”

Sleep­ing may even have impor­tant affects on depres­sion. Some researchers now believe that chronic sleep depri­va­tion may lead to depres­sion, rather than depres­sion caus­ing one to sleep less (which was what researchers used to think was the causal link).  In one study, which I believe is still ongo­ing, Harvey’s research group along with the Kaier Per­ma­nente Cen­ter for Health Research in Ore­gon recruited 60 mid­dle and high school stu­dents to inves­ti­gate whether more sleep can lower the risk fac­tor for depres­sion. In their study, the teens will report on their sleep habits for 12-weeks, under­go­ing 12 one-hour, once-a-week ses­sions of cog­ni­tive behav­ior ther­apy that will focus on sleep and mood patterns.

It’s clear then that sleep is adap­tive for many pos­i­tive outcomes.

“We are get­ting close to under­stand­ing some of the func­tions of sleep, yet soci­ety still treats sleep like a lux­ury. We say, ‘When I have two weeks’ vaca­tion I’m going to allow myself to sleep eight hours.’ But we would never say that about water or food. If there’s some­thing that gets short­changed, it’s always sleep,” notes Walker.

In fact, it turns out that peo­ple who take reg­u­lar naps and get a good night’s sleep may have the abil­ity to learn twice as much as those who just get a good night’s rest. This is all impor­tant research, espe­cially in light of the fact that about 40% of Amer­i­cans get less than 7 hours of shut-eye a night (teenagers are advised to sleep about 9 hours a night) and two-thirds of women report hav­ing dif­fi­culty falling asleep more than three nights a week. As Med­nick notes: “We are a sleep-deprived nation.” Med­nick and other offi­cials at UC San Diego even orga­nized a “nap-in” last year dur­ing Inter­na­tional Nap­ping Day (don’t you wish every day was Inter­na­tional Nap­ping Day?).

So, to all the nap­ping haters out there, check out the research. But really, doesn’t this research all really just con­firm what moth­ers have been telling us all along? Walker thinks so: “My research is not rev­o­lu­tion­ary, because your mother knew it all along.

—-  Scott Barry Kauf­man, Ph.D. is a cog­ni­tive psy­chol­o­gist and writer based in New York City. His lat­est Sharp­Brains arti­cles are:

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