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Study Shows Sleep Aids Memory


Research just published sheds new light on the surprising relationship between sleep and the ability of the brain to form memories. In fact, sleep may actually be an important part of the memory process.

Piano students may be told that "practice makes perfect," but at least when it comes to memorizing certain finger movements, it seems that practice may be only part of the story.

In an experiment conducted by researchers at Boston's Beth Israel Deaconess Medical Center and Harvard Medical School, participants practiced tapping out a sequence of numbers on a special keyboard. It's similar to the kind of memory skill a pianist might need in order to learn a piece of music. After 12 hours, the subjects were tested on how well they remembered the number sequence.

In some cases they got to sleep during that 12-hour period; in other cases they were tested later in the day, with no sleep in between. "And what we found," explained lead researcher Matthew Walker, "is that after you learn a memory task, you improve initially when you practice that memory task, but the brain doesn't stop learning, it turns out. Once you finish practice, the brain actually continues to learn in the absence of any further continued practice. However, that delayed learning, as it were, develops exclusively during sleep, and not during equivalent time periods when you're awake."

In the second stage, as they were trying to reproduce the finger movements they had memorized, the participants' brains were scanned using an MRI, to see what parts of the brain were involved. It turns out that different parts of the brain were active, depending on whether the subject had slept during that 12-hour period between learning and testing, or been awake.

During sleep, the brain apparently conducts what Dr. Walker calls "off-line memory processing" - in this case reorganizing the motor-skill memory for more efficient retrieval the next day.

Matthew Walker says this research is only the latest in a series of studies that has led scientists to recognize that the brain is quite busy during sleep. "We are starting to abandon the notion in science that the sleeping brain is simply a dormant brain. It turns out to be quite the contrary. In fact, parts of the brain can be up to 20-30% more active during certain kinds of sleep than when we're awake."

Dr. Walker says his study adds to an ample body of research that stresses the importance of getting a good night's sleep. "It's certainly additional evidence to suggest that sleep is critical - firstly in terms of our memory. From a more general perspective, though, I think it again just stresses that sleep is a biological necessity," he says. "Evolution has created sleep for a very specific reason, in fact probably for multiple reasons, and we have to start to learn that we can't shortchange either our brain or our bodies of sleep. Because there are consequences."

University students are famous for their poor sleep habits, and Dr. Walker says that includes the ones in his classes, despite their lessons about the importance of getting a good night's sleep. So I had to ask him about his own sleep habits. "That's a good question," he acknowledged, laughing. "Well, the irony of sleep research, in fact, is that I get very little of what I'm trying to study. But in some ways it's actually a great, subjective insight into the consequences of sleep deprivation. So I actually see it as an academic endeavor and a benefit rather than a hindrance."

Harvard Medical School Prof. Matthew Walker's study on sleep and memory was published in the most recent edition of the journal Neuroscience.

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