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Sleeping Brain, Learning Mind

By Matthew Walker

It has been 50 years since we discovered that the human brain does not lie dormant at night, but instead cycles through organized, discrete sleep stages. Yet we are only now getting close to understanding the function, or functions, of sleep. This evolving understanding, particularly of the interaction of sleep with learning and memory, holds important insights for students—and even for educators.

The theory that sleep is beneficial to our mental as well as physical abilities is not new. Sleep has been considered important in a variety of cognitive faculties ranging from creativity (e.g. the dreams of August Kekulé, which led to the conception of a simple structure for benzene, and those of Dmitry Mendeleyev that initiated the creation of the periodic table of elements) all the way to emotional healing (e.g. the works of the Freudian doctrine). Recent times have brought about a renewed interest in the effects of sleep on the brain—namely that sleep is crucial for consolidating certain types of memories. My own research has focused on this question, and the findings are ones I wished I’d known about back when I was a student.

The classical, textbook model of memory goes something like this: information is first acquired (such as learning a fact in class), and after acquisition comes a slowly developing process that solidifies the information into a more long-term, stable memory trace. This second stage of “memory consolidation” was, by this model, believed to unfold in a simple, time-dependent manner across hours or days.

However, our studies of skill memory (for example, the type of memory used in learning to play a musical instrument or learning sports) have provided a more refined picture. We have found that after a new memory is formed, it is initially vulnerable and susceptible to being lost, but across initial periods of time while a person is awake (somewhere in the region of six hours), the memory becomes more stable and less vulnerable.

But this is not the end of the process, as previously thought. An additional stage of consolidation then occurs, which actually improves the now-stable memory, so that when the information is recalled, performance is even better than it was after the memory was initially formed. That is to say the brain has continued to learn, even though it has stopped practicing.

We have discovered that this additional stage of “delayed” learning is absolutely dependent on sleep and, more specifically, on certain types of sleep at certain times of the night. Perhaps most worrying from the perspective of the student, or learner, is the finding that if you do not sleep the first night after learning this information, you lose the chance to develop the additional, memory-enhancing stage.

In fact, even if you have plenty of “recovery” sleep across subsequent nights after being deprived of sleep, you still cannot regain the sleep-dependent learning effect. Sleep deprivation, at least in terms of memory consolidation, is not like the bank. You cannot accumulate a debt and hope to pay it off in a lump sum at a later date. It is an all or nothing event, and if you don’t snooze, you lose.

So where does this leave us in real-life terms? Well, when I agreed to write this article, I was not so naive to think I would eradicate the now-common practice of the “all-nighter” prior to exam day—a practice that I’m sure is as old as formative examinations themselves. And, while I truly believe that sleep deprivation after the fact is devastating to those newly formed memories, perhaps I can think orthogonally. Perhaps I can offer an alternative suggestion.

If we as educators are striving for just that purpose—to educate—then I wonder if the traditional, all-encompassing exam at the end of the semester is the best option, since it seems to trigger a behavior quite oppositional to efficient memory development. While this examination method has been and continues to be debated, as a sleep researcher who understands the beneficial effects of a full night of shuteye, I can’t help thinking that logic, backed by scientific fact, must prevail.

We may therefore need to rethink our current evaluation methods and the strategy it forces our students to adopt. However, before any decisions are made as a result of these thoughts, I suggest that we all sleep on it!

Matthew Walker is Instructor in Psychiatry at Beth Israel Deaconess Medical Center.

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