Sleep research updates

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Scientists discover how cells responsible for wakefulness turn on and off

http://www.physorg.com/news100878624.html

Scientists may have discovered an underlying reason why individuals who suffer from sleep apnea, the disorder characterised by pauses in respiration during sleep, wake suddenly once they stop breathing.

Waking up when breathing stops during sleep and feeling faint during hyperventilation are common experiences. In an attempt to understand their neural basis, research led by scientists at the University of Cambridge focused on “orexin neurons”, brain cells recently found to be vital for normal wakefulness and breathing. The new experiments reveal that changes in brain acidity, which are tightly linked to breathing, can excite or silence these “wakefulness” cells. Inside the brain, much of communication is electrical, and involves neurons “firing” signals that travel along biological “wires” (axons) to other neurons. In the case of orexin neurons, the signals they generate are so important for steady consciousness that without them humans and animals become narcoleptic, suffering irresistible attacks of sleep and unconsciousness. The Cambridge and Oxford researchers found that rising levels of acid, such as those that occur during sleep apnea, released an electrical "brake" in orexin neurons. This allowed the neurons to fire faster. The brake consists of potassium pores in orexin cell membrane - when open, they stop neurons from firing. Rising acidity shuts down these pores, making orexin neurons fire very fast, while falling acidity opened the pores, silencing the firing. In the body, rises and falls in acidity are controlled by breathing. Acid is constantly made by the body's metabolism, but is normally prevented from building up because we breathe out “acidic” carbon dioxide. However, during sleep apnea the breathing stops, leading to a dangerous build up of acid in the brain. Acceleration of orexin cell by acid would dissipate this threat by causing awakening and increased breathing. Denis Burdakov of the University of Cambridge, who led the study, said: “Orexin neurons are among the most exciting discoveries in neuroscience since their activity has such striking effects on wakefulness and consciousness. We are thrilled to discover how this activity can be controlled”. One of the barriers to studying orexin cells is that they are sparse and few in number. To overcome this, the scientists used genetic engineering to make orexin cells fluorescent and so easier to see. Lars Fugger at Oxford, who carried out these genetic manipulations, said: “Our findings are important for understanding sleep disorders such as sleep apnea and narcolepsy. It is our aim to translate this research into a clinical setting that will benefit the patients afflicted by these diseases”. The paper "Control of hypothalamic orexin neurons by acid and CO2," is scheduled for publication in this week's edition of the Proceedings of the National Academy of Sciences (PNAS). Source: University of Cambridge » Next Article in Medicine & Health - Research: Researchers Reveal Structure of Protein Altered in Autism

 

 

A good night's sleep with the flip of a switch?

http://www.physorg.com/news97172057.html

The flip of a switch could become all it takes to get a good night's sleep, according to a study released Monday. Researchers at the University of Wisconsin-Madison have found a way to stimulate the slow waves typical of deep sleep by sending a harmless magnetic signal through the skulls of sleeping volunteers.

Sleep remains one of the big mysteries in biology. All animals sleep, and people who are deprived of sleep suffer physically, emotionally and intellectually. But nobody knows how sleep restores the brain.

 

 

 

Now, Giulio Tononi, a professor of psychiatry at the University of Wisconsin-Madison School of Medicine and Public Health, has discovered how to stimulate brain waves that characterize the deepest stage of sleep. The discovery could open a new window into the role of sleep in keeping humans healthy, happy and able to learn. The study was published in the April 30 edition of the Proceedings of the National Academy of Sciences. The brain function in question, called slow wave activity, is critical to the restoration of mood and the ability to learn, think and remember, Tononi says. During slow wave activity, which occupies about 80 percent of sleeping hours, waves of electrical activity wash across the brain, roughly once a second, 1,000 times a night. In a paper being published this week in the Early Edition of the scientific journal PNAS, Tononi and colleagues, including Marcello Massimini, also of the UW-Madison School of Medicine and Public Health, described the use of transcranial magnetic stimulation (TMS) to initiate slow waves in sleeping volunteers. The researchers recorded brain electrical activity with an electroencephalograph (EEG). A TMS instrument sends a harmless magnetic signal through the scalp and skull and into the brain, where it activates electrical impulses. In response to each burst of magnetism, the subjects' brains immediately produced slow waves typical of deep sleep, Tononi says. "With a single pulse, we were able to induce a wave that looks identical to the waves the brain makes normally during sleep." The researchers have learned to locate the TMS device above a specific part of the brain, where it causes slow waves that travel throughout the brain. "We don't know why, but this is a very good place to evoke big waves that clearly travel through every part of the brain," Tononi says.

Scientists' interest in slow waves stems from a growing appreciation of their role in sleep, Tononi says. "We have reasons to think the slow waves are not just something that happens, but that they may be important" in sleep's restorative powers. For example, a sleep-deprived person has larger and more numerous slow waves once asleep. And as sleep proceeds, Tononi adds, the slow waves weaken, which may signal that the need for sleep is partially satisfied. Creating slow waves on demand could someday lead to treatments for insomnia, where slow waves may be reduced. Theoretically, it could also lead to a magnetically stimulated "power nap," which might confer the benefit of eight hours sleep in just a few hours. Before that happens, however, Tononi must go further and prove that artificial slow waves have restorative benefits to the brain. Such an experiment would ask whether sleep with TMS leads to greater brain restoration than an equal amount of sleep without TMS. Although an electronic power-napper sounds like a product whose time has come, Tononi is chasing a larger quarry: learning why sleep is necessary in the first place. If all animals sleep, he says, it must play a critical role in survival, but that role remains elusive. Based on the fact that sleep seems to "consolidate" memories, many neuroscientists believe that sleeping lets us rehearse the day's events. Tononi agrees that sleep improves memory, but he thinks this happens through a different process, one that involves a reduction in brain overload. During sleep, he suggests, the synapses (connections between nerve cells) that were formed by the day's learning can relax a little. While awake, we "observe and learn much more than you think," he observes. "Tons of things are leaving traces, changing the synapses, mainly by making them stronger. It is wonderful that you can have all these synaptic traces in the brain, but they come at a price. Synapses require proteins, fats, space and energy. At the end of a waking day, you have all these traces of memories left behind. "During the slow waves, all the connections, step by step, are becoming a little weaker," Tononi adds. "By morning, the total connection strength is back to the way it was the morning before. The trick is to downscale all the connections by the same percentage, so the ones that were stronger are still stronger. That way you don't lose the memory." Without this type of weakening, he says, we "would not be able to learn new things" because our brains would lack sufficient available energy, space and nutrients. Although the explanation is still a hypothesis, Tononi hopes that the ability to artificially stimulate slow waves will allow him and other researchers to test the notion that sleep restores the brain by damping connectivity between neurons. Slow waves, he suspects, "Clear out the noise to make sure your brain does not become too much of an energy hog, a space hog. By morning, you have a brain that is energy efficient, space efficient and ready to learn again." Source: University of Wisconsin-Madison

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