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As people get older, they're less likely to get a good night's sleep and also less likely to remember things. Now scientists think they know why. NPR's Jon Hamilton reports.
JON HAMILTON, BYLINE: Sleep is when we turn short-term memories into memories that can last a lifetime. But Matt Walker at the University of California, Berkeley says exactly how the sleeping brain does this has been a mystery.
MATTHEW WALKER: What is it about sleep that seems to perform this elegant trick of cementing new facts into the neural architecture of the brain?
HAMILTON: To find out, Walker and a team of scientists had 20 young adults learn more than 100 pairs of words.
WALKER: And then we put electrodes on their head and we had them sleep.
HAMILTON: The researchers monitored the rhythmic electrical waves produced by the brain during deep sleep.
WALKER: And then the next morning, we actually performed a memory test.
HAMILTON: To see how many word pairs they remembered. And Walker says people remembered more pairs if two types of brainwaves had been highly synchronized during deep sleep.
WALKER: When those two brain waves were perfectly coinciding, that's when you seemed to get this fantastic transfer of memory within the brain from short-term, vulnerable storage sites to these more permanent, safe, long-term storage sites.
HAMILTON: Next, the team repeated the experiment with 32 people in their 60s and 70s. They remembered fewer word pairs than younger people had. And Walker says their brainwaves were less coordinated.
WALKER: It's like a drummer that's perhaps just one beat off the rhythm. The aging brain just doesn't seem to be able to synchronize its brain waves effectively.
HAMILTON: Randolph Helfrich, another member of the UC Berkeley team, says missing the beat by even a tiny amount can prevent the brain from hitting the save button on short-term memories.
RANDOLPH HELFRICH: So if you're, like, 50 milliseconds too early, 50 milliseconds too late, then this consolidation and storing mechanism actually doesn't work.
HAMILTON: The finding, which appears in the journal Neuron, could lead to a new way of treating memory problems. Matt Walker says that by delivering electrical or magnetic pulses through the scalp at night, it may be possible to re-synchronize brain waves that have lost the beat.
WALKER: What we're going to try and do is act like a metronome and, in doing so, see if we can actually salvage aspects of learning and memory in older adults and those with dementia.
HAMILTON: Walker says restoring rhythm in the brain also should improve the quality of their sleep.
Jon Hamilton, NPR News.
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