I can't pretend that I knew much when I was in college, but I knew one thing for sure: the "all-nighters" my dorm-mates were "pulling" were simply not for me. My body demanded sleep--and plenty of it--and I listened to the wisdom descending from my drowsiness dome. I went to bed early and rose early if I felt I needed some review before a big test. I avoided early afternoon classes. That was my naptime, when I could catch up on the critical ZZZs lost to all those wee-hours awakenings to the racket of all-night studiers dropping books, slamming doors, and cursing their grade-point averages. I watched them drag themselves off to class the next day in a zombie-like state and lament over dinner their poor performance on the big exam. Fortunately for me, most of them flunked out freshman year, so I got more sleep the longer I stayed in school.
I wasn't very analytical or knowledgeable about sleep in those days, but I trusted my instincts and I'm glad I did. If I considered the question "Why do we sleep?" at all during my college years, I probably thought of sleep as simply rest for a mind overfed on a steady diet of too-much-textbook. But in recent years--and since computers came along--I've come to think of sleep as performing the same functions as running the maintenance-utility package on my computer. You know how it works: One part of the software empties the trashcan and clears out the temporary files, old URLs, and cookies you've accumulated over a couple of weeks of Google mapping and Yahoo shopping. Another part mashes wandering worms and corrals wild viruses. My favorite part is the defragmenter. It takes all the saved stuff that's sprinkled all over the hard drive and consolidates it into what I think of as nice, neat, orderly packages. So, in practical terms, I think of sleep as the "housecleaning and tidy attacking" my brain needs to consolidate what's already come my way and get me ready for whatever is coming next.
That's why I'm not surprised that neuroscientists are finding more and more evidence of sleep as important to learning and memory. Like the utilities program in the computer, the sleep process in the brain throws out the trash and consolidates what's worth keeping. I admit I'm oversimplifying, but there's got to be a reason that some nerve cells in the brain fire five to ten times more often during certain sleep stages than they do during wakefulness. Maybe they are working hard to "clean up the mental hard drive." There just has to be a special function for dreaming, too, I'm convinced because, while overall brain activity diminishes during slow-wave sleep, it actually increases during dreaming.
"There is growing evidence that sleep serves to consolidate memories," Salk Institute neuroscientist Terrence Sejnowski told me in an interview a few years ago when I asked about such matters. "Both REM sleep and slow-wave sleep may have important, but different, roles." Sejnowski said that the brain constructs and reorganizes its circuits while we sleep. "When you make structural changes in your house, such as adding a new room, you temporarily move out so that the construction workers don't interfere with your life. During sleep, the brain is taken ‘offline' so that temporary and tentative changes made during the day can be made more permanent," he explained.
That made sense to me and, as I've continued to learn more about neuroscience in general and sleep specifically, I've become even more solidly convinced that my youthful instincts were correct. "Sleeping on it" improves both memory and performance.
A lot of research has focused lately on what researchers call hippocampus-dependent forms of memory, for which non-REM (all the sleep stages except rapid eye movement sleep) processes appear to be particularly beneficial. A number of studies have shown that the same kind of brain-neuron activity that occurs during awake-learning is repeated during non-REM sleep. Some researchers think that the reactivation and reorganization of memory traces during sleep enhances hippocampus-dependent learning-and perhaps other kinds of learning as well.
I am convinced that these researchers are on to something, so, naturally, a new piece of research in Current Biology caught my eye, as did the name of the study's most famous author, Robert Stickgold (shown left). (He's as well known among sleep researchers as Beyoncé is among music fans.) Researchers in Stickgold's lab at Harvard have been probing the relationship between sleep and learning for years, and this latest report adds a new piece of evidence to the growing body of research that will--someday, I hope--help us understand not only why we sleep but also how we learn.
In this new study, Stickgold and his coinvestigators put volunteers in front of a computer monitor and instructed them to learn a maze. The learners knew that, five hours later, they would be asked to find a path to a landmark tree from any randomly chosen spot within the maze. The learners were divided into two groups. Some took a nap after they learned the maze. Some did not, but they were instructed to think about the maze and the task while they remained awake.
As is usually found in experiments of this sort, the nappers did better later when they had to negotiate the maze than did the nonnappers. But that's not the end of it. Among the nappers, some reported having dreamed about the maze or the tree, while others did not. Although the nappers did consistently better than the nonnappers, the nappers who remembered dreaming about the maze or the tree did better yet. In other words, dreaming about the task improved memory or performance or both.
"We think that the dreams are a marker that the brain is working on the same problem at many levels," Stickgold said in a press release "The dreams might reflect the brain's attempt to find associations for the memories that could make them more useful in the future." Stickgold suggests that dreams aren't necessarily part of the memory-forming process, but that they serve as an indicator that memory processing is going on.
"What's got us really excited, is that after nearly 100 years of debate about the function of dreams, this study tells us that dreams are the brain's way of processing, integrating and really understanding new information," Stickgold told ScienceDaily. "Dreams are a clear indication that the sleeping brain is working on memories at multiple levels, including ways that will directly improve performance."
So I'm hoping that all those students who are taking exams this month or next will take heed. Don't stay up all night cramming for the test. Dream your way to the dean's list!
For Further Information:
I wrote about sleep and learning once before for this blog: "Get Smart: Take a Nap and You'll Learn Better."
The new Harvard study is Wamsley et al., "Report: Dreaming of a Learning Task Is Associated with Enhanced Sleep-Dependent Memory Consolidation." Current Biology 20, 1-6, May 11, 2010.
"To Learn Better, Take a Nap (and Don't Forget to Dream)," ScienceDaily (April 26, 2010).