Amid mounting evidence that sleep is key for your memory, researchers published a paper in the journal Science last week suggesting that playing specific sounds while a person sleeps—sounds connected to something that the person is trying to memorize—could help the memory sink in.
The researchers taught people to move 50 pictures to their correct locations on a computer screen. Each picture was accompanied by a related sound — meow for a cat, whirring for a helicopter, for example [The New York Times]. Next the test subjects lay down for a nap, and while they slept the researchers played sounds relating to half the objects. When the subjects woke up, scientists tested them on how well they remembered where each object went. Participants didn’t know they’d been subjected to the sounds while they napped, but they fared better at placing the objects for which they heard sounds in their sleep than those they didn’t.
Lead researcher Ken Paller explains: “While asleep, people might process anything that happened during the day — what they ate for breakfast, television shows they watched, anything…. But we decided which memories our volunteers would activate, guiding them to rehearse some of the locations they had learned an hour earlier” [U.S. News & World Report].
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For elephant seals, at least, there is some rest for the weary.
These marine mammals undertake epics migrations of thousands of miles, in which they might not return to land for as long at eight months. But elephant seals don’t have the same talent as whales and dolphins, which can have one hemisphere of their brains sleep while the other stays awake, so marine biologists weren’t sure how the seals managed to doze off while at sea. A new study in Biology Letters, however, suggests the seals might sleep as they drift slowly downward.
Past research had identified certain types of dives that include a period of slow descent that might be a siesta of sorts, for resting or digesting [The New York Times]. So scientists tagged a half-dozen young northern elephant seals off the California coast with instruments that tracked the seals’ positions and modeled their dives in three dimensions.
The monitors revealed that the seals periodically flip onto their backs and slip into slow, spiraling dives. The seals wobble as they drift down, and most of the time their bodies follow circular paths toward the bottom of the sea, said study co-author Russel Andrews…. “[They] resemble a leaf that has dropped from a tree branch and is falling toward the ground, fluttering from side to side,” he said [National Geographic]. It seems likely, the scientists say, that the seals catch a quick nap during these long drifts; in fact, once in a while they strike bottom without even noticing.
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Image: flickr / Mikebaird
Researchers have found a pharmaceutical way to clear some of the cognitive fog that results from a sleepless night. In a new study using lab mice, researchers corrected the memory problems in sleep-deprived mice through a drug that suppressed levels of a certain enzyme in a brain region called the hippocampus, which plays an important role in memory and learning.
The study, published in Nature, helps tease out the specific effects of sleep deprivation on the brain. Says lead researcher Christopher Vecsey: “One of the main problems is that sleep deprivation does a lot of things to the brain, and it’s easy to get caught in a mish-mash of different effects” [Nature News].
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Here’s yet another reason to get a good night’s rest: Researchers have found a link between the lack of sleep and the development of Alzheimer’s in mice.
The researchers studied levels of amyloid beta — a protein that accumulates in the brain of people with Alzheimer’s — in mice genetically engineered to have a version of Alzheimer’s disease. Amyloid levels rose in the brain when the mice were awake, and fell when they slept. When the researchers prevented the mice from sleeping, it made matters worse [Reuters]. Sleep deprivation accelerated the formation of plaques made of amyloid beta, they found.
The study, published in Science, may lead to other studies that examine whether people with chronic sleep problems are more likely to develop Alzheimer’s. Says lead researcher Jae-Eun Kang: “The hope would be to show that treating sleep problems in humans is important not just for the immediate effect of having a normal life, but also for the long-term effect of having a healthier brain” [Bloomberg].
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Image: iStockphoto
Some lucky people don’t groan awake to the alarm clock when they’ve only gotten six hours of sleep–instead they pop out of bed, bright-eyed and invigorated and ready for a new day. Now, researchers investigating the phenomenon of people who don’t need as much sleep as the rest of us have found a rare genetic mutation that accounts for some cases of shortened sleep cycles.
The scientists were searching the samples for variations in several genes thought to be related to the sleep cycle. In what amounts to finding a needle in a haystack, they spotted two DNA samples with abnormal copies of a gene called DEC2, which is known to affect circadian rhythms [The New York Times]. When they looked up the volunteers who had given the two DNA samples, they found a mother and daughter who habitually get about six hours of sleep each night and report no ill effects.
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Researchers have found good evidence that the troubling sleep disorder narcolepsy is an autoimmune disease, in which the body’s own immune system attacks healthy brain cells. A new study published in Nature Genetics links narcolepsy to mutations of two genes involved in critical roles in protecting the body from disease. These two variations, they say, are likely conspirators against [cells that produce] hypocretin, a hormone that promotes wakefulness, and that narcoleptics have been found to lack [HealthDay News].
Narcolepsy is a disruptive disorder that can trigger “sleep attacks” without any warning during any normal activity. In addition, some people can experience “cataplexy”, where strong emotions such as anger, surprise, or laughter can trigger an instant loss of muscle strength, which, in some cases, can cause collapse [BBC News]. There is currently no cure for narcolepsy, although the symptoms can be largely controlled with a mix of stimulants and sleep-suppressing medications.
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Researchers have found fundamental differences between the brains of people who prefer to rise and greet the dawn each day, and those who don’t mind seeing a sunrise, but only if it’s at the end of a long night. A new study used brain scans and alertness tests to probe the brains of early birds and night owls, and found that people tend to favor mornings or nights based at least in part on how they react to a kind of competition in the brain [National Geographic News].
Two factors control our bedtime. The first is hardwired: A master clock in the brain regulates a so-called circadian rhythm, which synchronizes activity patterns to the 24-hour day. Some people’s clocks tell them to go to bed at 9 p.m., others’ at 3 a.m…. The second factor–called sleep pressure–depends not on time of day but simply on how long someone has been awake already [ScienceNOW Daily News]. Sleep pressure builds up as hours of wakefulness increase. The new study, published in Science, suggests that early birds are more susceptible to sleep pressure, giving night owls the advantage in stamina.
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Researchers have another clue as to what’s happening in the brains of bleary-eyed air travelers suffering from jet lag: Two groups of brain cells become desynchronized, according to a new study. The study was undertaken in rats exposed to different amounts of light designed to simulate the effects of flying from Paris to New York…. “One group of neurons tells your body it is Paris time and another says that it is New York time. You are internally desynchronized,” [Telegraph], said lead researcher Horacio de la Iglesia.
The body’s circadian rhythm helps us keep track of when it’s time to eat, sleep, wake up and perform other body functions. This system is partly governed by the cycle of day and night. Changing time zones or working the late shift can throw off the body’s sense of timing because it changes the timing of our exposure to light [LiveScience]. The new study, published in Current Biology, examined a tiny section of the brain called the suprachiasmatic nucleus that controls circadian rhythms, and found that while one group of neurons adjusted to a time change relatively quickly, another group that governs dream-filled REM sleep can take up to a week to catch up.
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Sleep may be a way to sweep out the brain and get it ready for a new day of building connections between neurons, according to two new studies of fruit flies. The studies support the controversial theory that sleep weakens or entirely dissolves some synapses, the connections between brain cells. “We assume that if this is happening, it is a major function, if not the most important function, of sleep” [Science News], says Chiara Cirelli, a coauthor of the first study, published in Science.
Pruning synapses may be a practical necessity to keep the brain from being overwhelmed, says Paul Shaw, coauthor of the second study (also published in Science). “There are a number of reasons why the brain can’t indefinitely add synapses – including the finite spatial constraints of the skull. We were able to track the creation of new synapses in fruit flies during learning experiences – and to show that sleep pushed that number back down” [Telegraph], he says.
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It may be old news that people who work the night shift tend to have higher rates of certain medical conditions. But researchers say they have established a direct link between an abnormal sleep cycle and altered hormone levels, which can disrupt metabolism and increase the risk of heart disease, diabetes, and obesity. As soon as their circadian rhythms became separated from a day-night cycle, test subjects’ levels of key metabolic hormones went haywire—the most compelling evidence yet that shift work isn’t just an inconvenience, but an occupational hazard [Wired News].
The study, published in the Proceedings of the National Academy of Sciences, maps a clear path from work-sleep cycles to metabolic disregulation to disease [Wired News]. Scientists cannot yet explain the exact connection between metabolism and the circadian rhythm, the roughly 24-hour cycle that biological and behavioral processes are based on. But they believe the trigger to be a decrease in the hormone leptin, which the body uses to regulate appetite, that results when the circadian rhythm is disrupted.
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