in particular.
Students were given a series of math problems and prepped with a method to solve them. The students weren’t told there was also an easier “shortcut” way to solve the problems, potentially discoverable while doing the exercise. The question was: Is there any way to jump-start, even speed up, the insight into the shortcut? The answer was yes, if you allow them to sleep on it. If you let 12 hours pass after the initial training and ask the students to do more problems, about 20 percent will have discovered the shortcut. But, if in that 12 hours you also allow eight or so hours of regular sleep, that figure triples to about 60 percent. No matter how many times the experiment is run, the sleep group consistently outperforms the non-sleep group about three to one.
Sleep also has been shown to enhance tasks that involve visual texture discrimination (the ability to pick out an object from an ocean of similar-looking objects), motor adaptations (improving movement skills), and motor sequence learning. The type of learning that appears to be most sensitive to sleep improvement is that which involves learning a procedure. Simply disrupt the night’s sleep at specific stages and retest in the morning, and you eliminate any overnight learning improvement. Clearly, for specific types of intellectual skill, sleep can be a great friend to learning.
Why we sleep
Consider the following true story of a successfully married, incredibly detail-oriented accountant. Even though dead asleep, he regularly gives financial reports to his wife all night long. Many of these reports come from the day’s activities. (Incidentally, if his wife wakes him up—which is often, because his financial broadcasts are loud—the accountant becomes amorous and wants to have sex.) Are we all organizing our previous experiences while we sleep? Could this not only explain all of the other data we have been discussing, but also provide the reason why we sleep?
To answer these questions, we turn to a group of researchers who left a bunch of wires stuck inside a rat’s brain—electrodes placed near individual neurons. The rat had just learned to negotiate a maze when it decided to take a nap. The wires were attached to a recording device, which happened to still be on. The device allows scientists to eavesdrop on the brain while it is talking to itself, something like an NSA phone tap. Even in a tiny rat’s brain, it is not unusual these days to listen in on the chattering of up to 500 neurons at once as they process information. So what are they all saying?
If you listen in while the rat is acquiring new information, like learning to navigate a maze, you soon will detect something extraordinary. A very discrete “maze-specific” pattern of electrical stimulation begins to emerge. Working something like the old Morse code, a series of neurons begin to crackle in a specifically timed sequence while the mouse is learning. Afterward, the rat will always fire off that same pattern whenever it travels through the maze. It appears to be an electrical representation of the rat’s new maze-navigating thought patterns (at least, as many as 500 electrodes can detect).
When the rat goes to sleep, its brain begins to replay the maze-pattern sequence. Reminiscent of our accountant, the animal’s brain repeats what it learned that day. Always executing the pattern in a specific stage of sleep, the rat repeats it over and over again—and much faster than during the day. The rate is so furious, the sequence is replayed thousands of times. If a mean graduate student decides to wake up the rat during this stage, called slow-wave sleep, something equally extraordinary is observed. The rat has trouble remembering the maze the next day. Quite literally, the rat seems to be consolidating the day’s learning the night after that learning occurred, and an interruption of that sleep disrupts the learning cycle.
This naturally caused researchers to ask whether the same was true for humans. The answer? Not only do we do such processing, but we do it in a more complex fashion. Like the rat, humans appear to replay certain learning experiences at night, during the slow-wave phase. Unlike the rat, more emotionally charged memories appear to replay at a different stage in the sleep cycle.
These findings represent a bombshell of an idea: Some kind of offline processing is occurring at night. Is it possible that the reason we need to sleep is simply to shut off the exterior world for a while, allowing us to divert more attention to our cognitive interiors? Is it possible that the reason we need to sleep is so that we can learn?
It sounds compelling, but of course the real world of research is much messier. Some findings appear to complicate, if not fully contradict, the idea of offline processing. For example, brain-damaged individuals who lack the ability to sleep in the slow-wave phase nonetheless have normal, even improved, memory. So do individuals whose REM sleep is suppressed by antidepressant medications. Exactly how to reconcile these data with the previous findings is a subject of intense scientific debate. Newer findings in mice suggest that the brain uses the time to clean house, sweeping away the toxic molecules that are a byproduct of the brain doing its thinking. With more time and more research, we’ll gain a greater understanding of what the brain is doing as we sleep—and why.
For now, a consistent concept emerges: Sleep is intimately involved in learning. It is observable with large amounts of sleep; it is observable with small amounts of sleep; it is observable all the time. It is time we did a better job of observing its importance in our lives.
More ideas
If businesses and schools took sleep seriously, what would a modern office building look like? A modern school? These are not idle questions. The effects of sleep deprivation are thought to cost US businesses more than $100 billion a year.
Match schedules to chronotypes
Behavioral tests can easily discriminate larks from owls from hummingbirds. Given advances in genetic research, in the future you may need only a blood test to characterize your process C and process S graphs. That means you can determine the hours when you are likely to experience productivity peaks. Twenty percent of the workforce is already at suboptimal productivity in the current nine-to-five model. So here’s an obvious idea: Set your schedule—whether college class schedule or work schedule—to match your chronotype.
Businesses could create several work schedules, based on the chronotypes of the employees. They might gain more productivity and a greater quality of life for those unfortunate people who otherwise are doomed to carry a permanent sleep debt. A business of the future takes sleep schedules seriously.
We could do the same in education. Teachers are just as likely to be late chronotypes as their students. Why not put them together? You might increase the competencies of both the teacher and the students. Freed of the nagging consequences of their sleep debts, each might be more fully capable of mobilizing his or her God-given IQ.
Variable schedules also would take advantage of the fact that sleep needs change throughout a person’s life. For example, data suggest that students temporarily shift to more of an owl chronotype as they transit through their teenage years. This has led some school districts to start their high-school classes after 9:00 a.m. This may make some sense. Sleep hormones (such as the protein melatonin) are at their maximum levels in the teenage brain. The natural tendency of these kids is to sleep more, especially in the morning. As we age, we tend to get less sleep, and some evidence suggests we need less sleep, too. An employee who starts out with her greatest productivity in one schedule may, as the years go by, keep a similar high level of output simply by switching to a different schedule.
Respect the nap zone
Don’t schedule meetings or classes during the time when the process C and process S curves are flatlined. Don’t give high-demand presentations or take critical exams anywhere near the collision of these two curves. Can you actually get a nap? That’s often easier said than done. College students can perhaps get
