Sleep, Tetris, Memory and the Brain

As part of our ongo­ing Author Speaks Series, we are hon­ored to present today this excel­lent arti­cle by Dr. Shan­non Mof­fett, based on her illu­mi­nat­ing and engag­ing book. Enjoy!

(and please go to sleep soon if you are read­ing this late Mon­day night).
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Two years ago I fin­ished a book on the mind/brain, called The Three Pound Enig­ma: The Human Brain and the Quest to Unlock its Mys­ter­ies . Each chap­ter pro­files a leader in a dif­fer­ent aspect of mind/brain research, from neu­ro­surgery to zen Bud­dhism, from cog­ni­tive neu­ro­science to phi­los­o­phy of mind. One of my sub­jects was Dr. Robert Stick­gold, a zany, hyper-intel­li­gent men­sch of a Har­vard sleep researcher. When I met him, I was in med­ical school and hav­ing a grand old time—I’d exact­ed an exten­sion of my tenure beyond the cus­tom­ary four years, so I had enough time to write the book, do my course­work, and have a life. I was busy, but still got enough sleep, had time to exer­cise dai­ly, and even went for din­ner and a movie some­times. Although I found Stickgold’s work inter­est­ing, there was a part of me that just didn’t get it.

Fast-for­ward to the present, when I am a res­i­dent in emer­gency med­i­cine at a busy inner-city trau­ma cen­ter; I have two-year-old twins and a hus­band with a 60-hour-a-week job of his own. I do not exer­cise. I do not eat unless I can do some­thing else pro­duc­tive at the same time, and even when I do get to sleep in my own bed, my slum­ber is frac­tured by the awak­en­ings of two cir­ca­di­an­ly dis­parate tod­dlers. It seems to take me twice as long to “get” new con­cepts as it used to, and I nev­er feel like I’m func­tion­ing at top speed. In short, I am a mess. And NOW I get what Stickgold’s work is all about, and under­stand that he is both quan­ti­fy­ing and explain­ing exact­ly what I’m feeling.

Sleep is so obvi­ous a phys­i­o­log­ic need (from insects to mam­mals, all ani­mals sleep) that it doesn’t even occur to most of us to won­der why we have to do it—why in the world would we need to lie down, par­a­lyzed, for a third of our lives, with our brains in some sort of auto-pilot chaos? What do we get out of the process? It is aston­ish­ing how sparse is science’s answer to that ques­tion, but Stick­gold and oth­ers are begin­ning to pro­vide a solu­tion, and their answer ought to make any of us who are inter­est­ed in men­tal fit­ness sit up (or rather, lie down) and take notice.

When I met him, Stick­gold was just hit­ting his stride in what would turn out to be his spe­cial­ized area of research—the con­nec­tion between sleep and cog­ni­tion, and in par­tic­u­lar, between sleep and mem­o­ry. I had become inter­est­ed in his work part­ly because he was using non-tra­di­tion­al research tools: while many neu­ro­science exper­i­ments involve set­ting their sub­jects tedious made-up tasks, Stick­gold had heed­ed the sug­ges­tion of one of his under­grad­u­ate research assis­tants and was using video-games as his men­tal challenges.

Using the com­put­er-game Tetris he’d found what many of us knew anec­do­tal­ly: that just as they fall asleep after long Tetris prac­tice ses­sions, play­ers hal­lu­ci­nate images of the pecu­liar­ly-shaped Tetris tiles drift­ing down their fields of vision. It turns out, Stick­gold found, that even sub­jects with severe amne­sia, who couldn’t recall hav­ing played the game at all, had the same expe­ri­ence. He hypoth­e­sized that those images must have some­thing to do with a par­tic­u­lar kind of skill mem­o­ry, known as pro­ce­dur­al memory— the type of phys­i­cal mem­o­ry cre­at­ed when you prac­tice the vio­lin, or learn to play ten­nis, or write cal­lig­ra­phy. This type of mem­o­ry is often pre­served even in peo­ple with severe amne­sia. It seems like­ly that sleep is serv­ing to some­how orga­nize this type of mem­o­ry. And it turns out that with­out any fur­ther prac­tice, the sub­jects showed improve­ment in their Tetris scores after they’d “slept on” their new­found skill.

In a more tra­di­tion­al exper­i­ment, Stick­gold has shown that after a snooze, peo­ple per­formed much bet­ter on a recent­ly-learned fin­ger-tap­ping task than after the same amount of time with­out sleep. Even dou­bling the amount of time spent learn­ing the task had an insignif­i­cant per­for­mance ben­e­fit com­pared to sim­ply get­ting a night’s sleep between ses­sions. He lat­er showed that you don’t even need a whole night’s sleep but that an hour’s nap can give you the same learn­ing ben­e­fits (thank Heav­ens, I say, from my new van­tage-point as a sleep-scavenger).

Stick­gold also showed that sub­jects who weren’t allowed to sleep soon after learn­ing a new skill nev­er regained the lost ben­e­fit, and—unless giv­en more practice/sleep cycles—never got quite as good at the skill as those who’d been allowed to sleep soon after their train­ing sessions.

More recent­ly, Stickgold’s lab has shown that sleep makes a stun­ning dif­fer­ence in the abil­i­ty of a par­tic­u­lar kind of mem­o­ry known as “declarative” mem­o­ry to with­stand inter­fer­ence. Declar­a­tive mem­o­ry has to do with facts: what you ate for break­fast today, where you last put your keys, what you read in this morning’s paper—all of these are declar­a­tive mem­o­ries. In an ele­gant exper­i­ment, Stick­gold taught a group of peo­ple a list of word-pairs. Then one half the group was sent off to bed, while the oth­er half was asked to remain awake.

At the end of the wait­ing peri­od, half the sleep­ers and half the awake sub­jects were taught anoth­er set of “interference” words, pairs designed to con­fuse the mem­o­ry of the orig­i­nal pair­ings. Imme­di­ate­ly after­ward, all sub­jects were test­ed on the ini­tial word-pairs. The group that had received the inter­fer­ence teach­ing but slept before­hand aver­aged about 76% on the test. The group that received the inter­fer­ence train­ing but had remained awake between the two ses­sions aver­aged about 32%.

Appar­ent­ly, just sleep­ing on the new infor­ma­tion had some­how cement­ed it into subjects’ minds so that it was resis­tant to inter­fer­ence. To those of us who are des­per­ate to retain—accurately—the new infor­ma­tion with which we are bom­bard­ed each day, such research is eye-open­ing, and poten­tial­ly life-changing.

Stick­gold is not the only sci­en­tist study­ing human sleep, of course—there are oth­ers work­ing on sleep and cog­ni­tion (most with results sim­i­lar to Stickgold’s), and more researchers pro­vid­ing con­vinc­ing evi­dence that sleep boosts your immune sys­tem, improves your mood, and—oh yeah—helps you stay awake when you want to be. There is also evi­dence that get­ting poor or insuf­fi­cient sleep rais­es your risk of obe­si­ty, heart dis­ease and dia­betes; increas­es your blood pres­sure; and makes you acci­dent-prone: all great rea­sons to get a good night’s sleep (which, accord­ing to sci­en­tists, is 8–9 hours of unin­ter­rupt­ed slum­ber). Yet, like many Amer­i­cans, I am more moti­vat­ed by the stud­ies show­ing sleep’s cog­ni­tive ben­e­fits. I had been going to go hit the books when I fin­ished this piece—now I think I’ll just hit the hay. Maybe you should, too.

– Shan­non Mof­fet has an MD from Stan­ford Uni­ver­si­ty School of Med­i­cine, and is in her res­i­den­cy in emer­gency med­i­cine at High­land Hos­pi­tal in Oak­land, CA. Her book on the brain (and eight dynam­ic brain-mavens, includ­ing Robert Stick­gold) is The Three Pound Enig­ma: The Human Brain and the Quest to Unlock its Mys­ter­ies. Mof­fett recent­ly appeared on The Brain Fit­ness Pro­gram, which aired nation­wide on PBS.