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A BCC High School parent (who is Chief of  Behavioral & Integrative Neuroscience Research Branch and the Coordinator for Sleep Research at NIMH) spotted the following article for us.  He said, “There are a lot of articles on sleep around, but I found this one to be particularly comprehensive and written in general terms so that it captures a huge segment of where the research is at and what it tells us.”  It is particularly timely for parents whose kids are approaching their final exams, especially “Link to Learning,” the last section of the article which describes a Harvard study showing that people who didn’t sleep after learning something new didn’t retain what they had learned.

By Ronald Kotulak, Tribune science reporter. 

To sleep, perchance to build an infant's brain, perchance to learn, perchance to heal, perchance to grow, perchance to clear the cobwebs, perchance to slow aging, perchance to stay slim, perchance to renew, perchance to prevent depression and dementia, and, oh yes, perchance to dream. 

As researchers explore one of the biggest mysteries of biology--why we need sleep--a consensus is emerging that far more things go on during sleep than anyone ever dreamed. Practically every function of the body undergoes dramatic changes. 

Because sleep serves so many purposes, not getting enough of it appears to have a broad effect on health. In fact, the chronic sleep deprivation suffered by most Americans may be contributing to the modern epidemics of obesity, diabetes and hypertension. 

"We need sleep for almost everything," said Eve van Cauter, a University of Chicago professor of medicine and a leading sleep researcher. "Studies are beginning to show that no matter what system you look at--whether it's memory, learning, the immune system, endocrine system or sugar metabolism--when you look at those systems in subjects who are sleep deprived on a chronic basis, you find negative effects." 

Sleep has been a great puzzle to science, despite the fact that all animals sleep. Even fruit flies sleep. Dolphins sleep with half of their brain at a time so that the other half can bring them to the surface to breathe. Cows sleep standing up, birds sleep perched on limbs, and nocturnal animals sleep during the day. 

Now researchers believe they are hot on the trail. For the first time they have a reasonable theory and growing evidence of how sleep evolved, why we still need it, and how cheating on sleep may be more damaging than generally believed. 

Modern science's amazing new tools--from brain scans to molecular biology to genetic engineering--are uncovering the brain's centers for sleep and wakefulness, natural chemicals in the brain that make people sleep or keep them awake, and hormonal changes that repair the wear and tear of the day. 

"More progress has been made in the last six to eight years in understanding how and why we sleep than in the prior 100 years," said David Dinges, chief of the University of Pennsylvania's division of sleep and chronobiology. 

Besides contributing to our basic understanding of sleep, Dinges' research has unsettling ramifications for a sleep-deprived nation. The average American gets somewhat less than seven hours a night, one to 1 1/2 hours short of what Dinges finds to be most efficient. 

Not up to par

People who regularly don't get enough sleep may think they're doing OK, but Dinges' studies indicate their alertness and mental performance may be below par. 

In his research, healthy middle-aged volunteers were permitted varying amounts of sleep and then asked to perform tasks on a computer or driving simulator. Among those allowed only six hours of sleep per night, one in four began to have serious sleep attacks--that is, they fell asleep against their will--by the sixth day of testing. In the group limited to four hours of sleep a night, one in two had sleep attacks by day six. 

"Motivation alone isn't enough to keep you from drifting off or having an uncontrolled sleep attack," Dinges said. "That's what then seems to lead to a potentially catastrophic outcome if you're operating a train or a car." 

Volunteers who got a nightly average of eight hours of sleep during the two-week experiment did not have a single sleep attack.

Van Cauter's findings are just as disturbing. "We're really driving ourselves to sleep as little as possible and people are not recognizing that this is harmful," she said. "It's time now to recognize that chronic sleep loss may be as bad as smoking, as bad as a poor diet, and as bad as a lack of exercise for our health and cognitive function." 

Her research shows that lack of sleep in healthy young people causes many of their hormone systems to malfunction. Growth hormones, for instance, which are important for tissue repair and growth, decrease. The stress hormone cortisol also increases during the night when it should decline, potentially endangering brain cells. 

And insulin, which is critical for metabolizing food, no longer does its job properly. When insulin has a tougher time converting glucose from the food we eat into energy or fat, the body has to make two to three times the normal amount. This is a condition called insulin resistance, and it is now believed to be the first step on the way to type 2 diabetes. 

At the same time, leptin, a hormone that normally tells your brain that you're full and that you should stop eating, declines, making you hungry and wanting to eat more. 

"Our work suggests that we are paying a price in that there are indications that the so-called epidemics of obesity and diabetes might be partly related to our sleep habits," van Cauter said. "Even with an excellent diet and with exercise, if you don't sleep enough you are more at risk for putting on weight." 

The body has two basic sleep systems that are different, but complementary. One is regulated by neurotransmitters in the brain that tell you whether you should be asleep or awake; the other is the circadian system, which tells you when it's appropriate to sleep, which is usually at night. 

A critical chemical

Keeping the brain bright and alert is the main job of a chemical called hypocretin or sometimes orexin--something no one knew until Emmanuel Mignot of Stanford University discovered the gene that causes narcolepsy in dogs. Narcolepsy is a condition in which sleep comes without warning at inappropriate times. 

A mutated gene inherited by the narcoleptic dogs failed to make the right kind of hypocretin, so they fell asleep. Hypocretin's role became obvious--it keeps the brain awake. 

In humans, Mignot found that it wasn't a mutated gene that caused narcolepsy but the total absence of the chemical in the brain. Further study showed that the 10,000 brain cells that normally make hypocretin had died off in these patients. It's possible that an autoimmune reaction killed them off in the same way that insulin-secreting beta cells are destroyed in children to cause type 1 diabetes. 

In a way, the brain is like a construction site that runs on day and night shifts. During the day, hypocretin is normally busy keeping the brain awake at a time when new experiences are pouring in through the senses. 

At night, sleep-inducing brain chemicals take over. It is then that the brain's architect comes out and tells workers which experiences to keep, what memories to build out of them and which experiences to discard. 

As the brain receives enormous amounts of input from the outside world during the day, many important neurotransmitters are produced. One of the jobs of these compounds is to act as sleep inducers--they reach their highest level when the need for sleep is the greatest. 

So powerful are these chemicals that when they are injected into the brains of mice, the animals go to sleep. 

Many of these hormones activate a major sleep switch in the hypothalamus, right behind the eyes. Once triggered into action, the sleep center sends out chemical messengers that tell the brain to turn off the chemicals that are keeping it awake--hypocretin among them. 

If this sleep switch is removed in animals, it eliminates 60 to 70 percent of their sleep, said Clifford B. Saper of Harvard University. 

The discovery of the gene that produces hypocretin came on the heels of the discovery of the first circadian rhythm gene, called the clock gene, in 1997 by Northwestern University's Joseph Takahashi, Lawrence Pinto and Fred Turek. Since then, eight other circadian genes have been found, the most recent this year by the Northwestern team. 

The circadian system is thought to have evolved because night is a hazardous time for humans to be up and about--the darkness makes it difficult to avoid danger. 

The Northwestern team found that the master circadian rhythm is run by a center in the brain. But every organ system, such as the liver and heart, also has its own circadian genes. The liver, for example, needs to keep its own time in order to be ready to metabolize food at meals. 

Jet lag occurs when we fly six or eight hours ahead or behind our normal cycle, throwing our organ clocks and brain clock out of sync, Takahashi said. 

Why do we sleep?

But it is the question of why we sleep, rather than when or how often, that intrigues scientists the most. One emerging theory says sleep would have evolved in the first primitive organism that developed a nerve cell, in order to give that cell time to process information it receives from the environment. 

Neurobiologist James Krueger of Washington State University, Pullman, is among the scientists who believe the growth hormones that are produced as a result of daytime experiences have a dual role. 

They first induce unconsciousness so that they then can construct the microcircuitry of the brain to reflect the day's learning. 

"Your brain at the end of the day is different than your brain at the beginning of the day," he said. "The microcircuitry of your brain is constantly changing. It's never the same from one minute to the next. 

"There has to be some process in the brain that somehow conserves behaviors that are characteristic of a species," Krueger added. "There also has to be something that preserves circuits that are responsible for memories." 

His idea is that sleep helps the brain preserve those genetic characteristics and learned memories. 

To test the theory, scientists in Switzerland had subjects hold a vibrating object in their right hand. Later, during sleep, the left side of their brain--which controls the right hand--showed a more active sleep pattern than the side that was not stimulated. 

Other researchers gave volunteers math and verbal problems before going to bed and found that the parts of their brain that process math and language were more active during sleep. 

Then two reports came out this year showing that sleep seems to be essential for learning and for building the infant brain. 

Matt Wilson of the Massachusetts Institute of Technology measured brain waves of rats learning a maze and found that during sleep those parts of the brain involved in learning displayed the same brain wave pattern that occurred when the animals were running through the maze. It was as if the rats were practicing in their sleep. 

And a study on kittens by Michael P. Stryker, chief of physiology at the University of California at San Francisco, showed why newborns of all species sleep so much: It's a time when their brains are being wired to adapt to their surroundings. 

Newborn kittens develop sight during the first three or four weeks of life. After closing one of the kittens' eyes, Stryker exposed the animals to a new visual learning experience for six hours. When the kittens then were allowed to sleep, nerves that transmit images from the eye to the brain grew connections to the visual cortex. If they did not sleep, very few connections were made from the uncovered eye to the brain. The closed eye did not show any nerve growth. 

Many neuroscientists believe the same process used to build connections between brain cells in a newborn essentially is reused for learning and memory later in life. 

"This suggests a role for why we sleep," Stryker said. "Something about sleep is important to the processes which are responsible for making precise connections in the brain." 

The link to learning 

A similar link between sleep and learning was found by Robert Stickgold of Harvard. When volunteers were given a task to learn, their ability to remember more and improve their performance increased significantly if a good night's sleep followed the training. 

Surprisingly, volunteers who had the same amount of learning but who were not allowed to sleep that night failed to retain what they had learned. 

"It you don't get sleep that first night, it's done," Stickgold said. "You can't make it up the second or third night. Something happens in the brain during that first night of sleep that alters, moves, refines or strengthens the brain's representation of that experience to convert it into a form that can actually support improved performance at retesting." 

The news is bad for students who like to study all night before exams. They may do all right on the test because they can retain enough for a short period. But invariably the students say they can't remember three days later what they studied, Stickgold said. 

Those findings fit well with Krueger's theory, that sleep developed to enable nerves to process information. Then, it seems, nature also began to use sleep for other purposes, such as memory, readjusting hormones, repairing the body, fighting infections and other functions. 

It's like the lungs. They evolved to exchange oxygen and carbon dioxide, but later they also were put to use to produce voice. Nature likes to reuse things that work. 

"We're not going to have adequate explanations for really important functions of the brain, things like emotions, memory and consciousness, until we can provide a good explanation for why it is you need sleep," Krueger said.