Saturday, November 28, 2009

WAKING UP MEMORIES WHILE YOU SLEEP

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They were in a deep sleep, yet sounds, such as a teakettle whistle and a cat's meow, somehow penetrated their slumber.

The 25 sounds presented during the nap were reminders of earlier spatial learning, though the Northwestern University research participants were unaware of the sounds as they slept.

Yet, upon waking, memory tests showed that spatial memories had changed. The participants were more accurate in dragging an object to the correct location on a computer screen for the 25 images whose corresponding sounds were presented during sleep (such as a muffled explosion for a photo of dynamite) than for another 25 matched objects.

"The research strongly suggests that we don't shut down our minds during deep sleep," said John Rudoy, lead author of the study and a neuroscience Ph.D. student at Northwestern. "Rather this is an important time for consolidating memories."

Most provocatively, the research showed that sounds can penetrate deep sleep and be used to guide rehearsal of specific information, pushing people's consolidation of memories in one direction over another.

"While asleep, people might process anything that happened during the day -- what they ate for breakfast, television shows they watched, anything," said Ken Paller, senior author of the study and professor of psychology in the Weinberg College of Arts and Sciences at Northwestern. "But we decided which memories our volunteers would activate, guiding them to rehearse some of the locations they had learned an hour earlier."

The Northwestern study adds a new twist to a growing body of research showing that memories are processed during sleep. It substantiates the literature showing that the brain is very busy during sleep, going over recently acquired information and integrating it with other knowledge in a mysterious consolidation process that sustains our memory abilities when awake.

"Strengthening Individual Memories by Reactivating Them During Sleep" will be published in the journal Science. Besides Paller and Rudoy, the paper's co-authors are Northwestern colleagues Joel L. Voss and Carmen E. Westerberg.

Whether or not memories are processed during sleep has been a subject of controversy, with most of the research on the topic focusing on REM, a normal stage of sleep characterized by rapid movement of the eyes. Vividly recalled dreams mostly occur during REM sleep. Recent research, including the new Northwestern study, however, focuses on memory processing during deep sleep, rather than during REM sleep.

"We are beginning to see that deep sleep actually is a key time for memory processing," Paller said.

Prior to their naps, the 12 study participants were taught to associate each of 50 images with a random location on a computer screen. Each object, such as a shattering wine glass, was paired with a corresponding sound, such as that of breaking glass, delivered over a speaker.

Locations were learned by repeating trials until study participants got quite good at placing all the objects in their assigned places. Approximately 45 minutes after learning, each participant reclined in a quiet, darkened room. Electrodes attached to their scalp measured their brain activity, indicating when they were asleep. Sleep sounds were presented without waking anyone up. When asked later, none of the participants thought sounds had been played during the naps. Yet, memory testing showed that placements of the objects were more accurate for those cued by their associated sounds during sleep than for those not cued.

"Our little experiment opens the door to many questions," Paller said.

Would high-school students do better on SAT tests if daytime studying was supplemented with sleep sounds at night? Would students learning foreign vocabulary words or other facts do better in the morning after listening to related information as they slept? Infants spend an inordinate amount of time sleeping, while their brains work over their recent experiences. Could an infant learn a first language more quickly if stimulation occurred during naps or overnight? What about an actor trying to learn lines or a law student trying to memorize numerous details of case law? Could playing sounds related to such learning improve the recall of relevant facts the next day?

The study opens avenues for discovering boundaries of what can happen to memories during sleep, said co-author Voss. "Can memories be distorted as well as strengthened? Can people be guided to forget unwanted memories?"

Much work remains to determine whether the results of the new research translate to these and other contexts, Paller emphasized. "We don't know the answers at this point," he said, "but more experiments about memory processing during sleep are certain to follow."

Northwestern University

STUDY RAISES CONCERNS ABOUT OUTDOOR SECOND-HAND SMOKE

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Indoor smoking bans have forced smokers at bars and restaurants onto outdoor patios, but a new University of Georgia study in collaboration with the Centers for Disease Control and Prevention suggests that these outdoor smoking areas might be creating a new health hazard.

The study, thought to be the first to assess levels of a nicotine byproduct known as cotinine in nonsmokers exposed to second-hand smoke outdoors, found levels up to 162 percent greater than in the control group. The results appear in the November issue of the Journal of Occupational and Environmental Hygiene.

"Indoor smoking bans have helped to create more of these outdoor environments where people are exposed to secondhand smoke," said study co-author Luke Naeher, associate professor in the UGA College of Public Health. "We know from our previous study that there are measurable airborne levels of secondhand smoke in these environments, and we know from this study that we can measure internal exposure.

"Secondhand smoke contains several known carcinogens and the current thinking is that there is no safe level of exposure," he added. "So the levels that we are seeing are a potential public health issue."

Athens-Clarke County, Ga., enacted an indoor smoking ban in 2005, providing Naeher and his colleagues and ideal environment for their study. The team recruited 20 non-smoking adults and placed them in one of three environments: outside bars, outside restaurants and, for the control group, outside the UGA main library. Immediately before and after the six-hour study period, the volunteers gave a saliva sample that was tested for levels of cotinine, a byproduct of nicotine and a commonly used marker of tobacco exposure.

The team found an average increase in cotinine of 162 percent for the volunteers stationed at outdoor seating and standing areas at bars, a 102 percent increase for those outside of restaurants and a 16 percent increase for the control group near the library.

Naeher acknowledges that an exposure of six-hours is greater than what an average patron would experience but said that employees can be exposed for even longer periods.

"Anyone who works in that environment—waitresses, waiters or bouncers—may be there for up to six hours or longer," Naeher said. "Across the country, a large number of people are occupationally exposed to second-hand smoke in this way."

Studies that measured health outcomes following indoor smoking bans have credited the bans with lowering rates of heart attacks and respiratory illness, but Naeher said that the health impacts of outdoor second-hand smoke are still unknown.

In Naeher's study, cotinine levels in the volunteers at the bar setting saw their levels increase from an average pre-exposure level of 0.069 ng/ml (nanograms per milliliter) to an average post-exposure level of 0.182 ng/ml. The maximum value observed, however, was 0.959 ng/ml. To put that number into context, a widely cited study has determined that an average cotinine level of 0.4 ng/ml increases lung cancer deaths by 1 for every 1,000 people and increases heart disease deaths by 1 for every 100 people.

Still, the researchers caution that it's too early to draw policy conclusions from their findings. Cotinine is a marker of exposure to tobacco, Naeher said, but is not a carcinogen. The team is currently planning a study that would measure levels of a molecule known as NNAL, which is a marker of tobacco exposure and a known carcinogen, in people exposed to second-hand smoke outdoors.

"Our study suggests that there is reason to be concerned about second-hand smoke levels outdoors," said study co-author Gideon St. Helen, who is pursuing his Ph.D. through the university's Interdisciplinary Toxicology Program, "and our findings are an incentive for us to do further studies to see what the effects of those levels are."

University of Georgia

STUDY: SEA STARS BULK UP TO BEAT THE HEAT

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A new study finds that a species of sea star stays cool using a strategy never before seen in the animal kingdom. The sea stars soak up cold sea water into their bodies during high tide as buffer against potentially damaging temperatures brought about by direct sunlight at low tide.

"Sea stars were assumed to be at the mercy of the sun during low tide," said the study's lead author, Sylvain Pincebourde of François Rabelais University in Tours, France. "This work shows that some sea stars have an unexpected back-up strategy."

The researcher is published in the December issue of The American Naturalist.

Sea stars need to endure rapid changes in temperature. During high tide, they are fully submerged in cool sea water. But when tides receded, the stars are often left on rocky shorelines, baking in the sun.

Clearly the stars had some way of beating the heat, but scientists were unsure how they did it. Pincebourde and his team thought it might have something to do with fluid-filled cavities found in the arms of sea stars. So he set up an experiment to test it.

The researchers placed sea stars in aquariums and varied the water level to simulate tidal patterns. Heat lamps were used to control temperature, with some stars experiencing hotter temperatures than others. The researchers found that stars exposed to higher temperatures at low tide had higher body mass after the high tide that followed. Since the stars were not allowed to eat, the increased mass must be from soaking up water.

"This reservoir of cool water keeps the sea star from overheating when the tide recedes again the next day, a process called 'thermal inertia,'" Pincebourde said.

What appears to be happening, the researchers say, is that a hot low tide serves as a cue telling the star to soak up more water during the next high tide. And the amount of water the stars can hold is remarkable.

"It would be as if humans were able to look at a weather forecast, decide it was going to be hot tomorrow, and then in preparation suck up 15 or more pounds of water into our bodies," said co-author Brian Helmuth of the University of South Carolina in Columbia.

The researchers are concerned, however, that climate change may put this novel cooling strategy in peril.

"This strategy only works when the sea water is colder than the air," said co-author Eric Sanford of the University of California, Davis. "Ocean warming might therefore break down this buffering mechanism, making this sea star susceptible to global warming. There are likely limits to how much this mechanism can buffer this animal against global change."

University of Chicago

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