Direct Recording Shows Brain Signal Persists Even in Dreamless Sleep

Neuroscientists at Washington University School of Medicine in St. Louis have taken one of the first direct looks at one of the human brain's most fundamental "foundations": a brain signal that never switches off and may support many cognitive functions.

The results, appearing online this week in the Proceedings of the National Academy of Sciences, are an important step forward for efforts to outline what neuroscientists call the functional architecture of the brain. Better understanding of this architecture will aid efforts to treat brain injury and mental disorders, the researchers say.

Although the brain's different specialized regions can be considered as a collection of physical structures, functional architecture instead focuses on metaphorical structures formed by brain processes and interactions among different brain regions. The "foundation" highlighted in the new study is a low-frequency signal created by neuronal activity throughout the brain. This signal doesn't switch off even in dreamless sleep, possibly to help maintain basic structure and facilitate offline housekeeping activities.

"A different, more labile and higher-frequency signal known as the gamma frequency activity has been the focus of much brain research in recent years," says first author Biyu He, a graduate student. "But we found that signal loses its large-scale structure in deep sleep, while the low-frequency signal does not, suggesting that the low-frequency signal may be more fundamental."

"What we've been finding is reorienting the way we think about how the brain works," says senior author Dr. Marcus Raichle, M.D., professor of radiology, of neurology and of neurobiology. "We're starting to see the brain as being in the prediction business, with ongoing, organized carrier frequencies within the systems of the brain that keep them prepared for the work they need to do to perform mental tasks."

Neurologists have already spent many years exploring the upper levels of the brain's functional architecture. In these studies, researchers typically ask volunteers to perform specific mental tasks as their brains are scanned using functional magnetic resonance imaging (fMRI). Such "goal-oriented" tasks might include looking for or studying a visual stimulus, moving an arm or leg, reading a word or listening for a sound. As the subjects perform these tasks, the scans reveal increases in blood flow to different parts of the brain, which researchers take as indications that the brain areas are contributing to the mental task.

In the past decade, though, scientists have realized that deeper structures underlie goal-oriented mental processes. These underlying brain processes continue to occur even when subjects aren't consciously using their brain to do anything, and the energies that the brain puts into them seem to be much greater than those used for goal-oriented tasks.

"The brain consumes a tremendous amount of the body's energy resources—it's only 2 percent of body weight, but it uses about 20 percent of the energy we take in," says Raichle. "When we started to ask where all those resources were being spent, we found that the goal-oriented tasks we had studied previously only accounted for a tiny portion of that energy budget. The rest appears to go into activities and processes that maintain a state of readiness in the brain."

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Nurses Working Extended Shifts Tired at Work, Sleep Little Are Likely to Drive Drowsy

Hospital staff nurses who work extended hours, work at night, struggle to remain awake at work, or obtain less sleep are more likely to experience a drowsy driving episode, according to a study published in the Dec. 1 issue of the journal Sleep.

The study, authored by Linda Scott, of Grand Valley State University in Grand Rapids, Mich., focused on data that were collected from 895 full-time hospital staff nurses, who completed logbooks on a daily basis for four weeks providing information concerning work hours, sleep duration, drowsy and sleep episodes at work, and drowsy driving occurrences.

According to the results, almost 67 percent of the nurses reported at least one episode of drowsy driving, and three percent reported experiencing drowsy driving following every shift worked. On average, nurses reported experiencing an episode of drowsy driving one out of every four shifts they worked.

Two-hundred eighty-one episodes of motor vehicle crashes/near-motor vehicle crashes were reported during the study period. The majority of these incidents occurred following shifts that exceeded 12.5 hours in duration. The likelihood of a motor vehicle crash/near-motor vehicle crash significantly increased with longer shift durations. The risk for a motor vehicle crash/near-motor vehicle crash almost doubled when driving following shifts that exceeded 12.5 hours.

The risk for a drowsy driving episode doubled when nurses worked 12.5 or more consecutive hours. Working at night also significantly increased the risk for drowsy driving incident. In fact, 79.5 percent of the nurses who worked only night shifts reported at least one episode of drowsy driving.

Almost two-thirds of the nurses reported struggling to stay awake at work at least once during the study period, and 16.9 percent of the nurses actually fell asleep at least one during their work shift. Nurses who struggled to stay awake at work were significantly more likely to report struggling to stay awake driving home after work. In particular, the likelihood of a drowsy driving incident was tripled when nurses experienced episodes of drowsiness at work. The risk for a drowsy driving episode was also increased when nurses reported falling asleep on duty.

Although research on the effects of chronic sleep restriction has revealed that most adults require at least seven to eight hours of sleep each night to avoid developing chronic sleep debt with its accompanying performance deficits, the hospital staff nurses in this study frequently obtained less sleep than this critical threshold. Only 20.8 percent of the participants reported obtaining at least six hours of sleep prior to every shift they worked. The risk for a drowsy driving episode increased by nine percent for each hour of sleep lost.

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Sleep Disorders Highly Prevalent Among Police Officers

Sleep disorders are common, costly and treatable, but often remain undiagnosed and untreated. Unrecognized sleep disorders adversely affect personal health and may lead to chronic sleep loss, which, in turn, increases the risk of accidents and injuries. These problems are exacerbated in shift workers such as police officers, who may experience chronic sleep loss due to their schedules.

A sampling of police officers shows a high incidence of sleep disorders among the members of this profession, according to a research abstract that was to be presented at SLEEP 2007, the 21st Annual Meeting of the Associated Professional Sleep Societies (APSS).

The study, authored by Shantha Rajaratnam, of Harvard Medical School, was based on the responses of 4,471 police officers to a self-report survey that included screening for obstructive sleep apnea (OSA) alone or for OSA and insomnia, restless legs syndrome (RLS), shift work sleep disorder and narcolepsy with cataplexy.

The percentage of those who screened positive for any sleep disorder was 38.4 percent, including 35.1 percent for OSA, 6.8 percent for insomnia, 0.7 percent for RLS, two percent for shift work sleep disorder and 0.5 percent for narcolepsy. These individuals were referred to a sleep clinic for a formal evaluation.

"Based on these data, sleep disorders appear to be highly prevalent in the present sample of police officers," says Rajaratnam. "Sleep disorder screening and treatment programs may potentially improve police officer health, safety and productivity."

The amount of sleep a person gets affects his or her physical health, emotional well-being, mental abilities, productivity and performance. Recent studies associate lack of sleep with serious health problems such as an increased risk of depression, obesity, cardiovascular disease and diabetes.

Experts recommend that adults get between seven and eight hours of sleep each night to maintain good health and optimum performance.


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Start School Later in the Morning, Say Sleepy Teens

A survey of sleep-deprived teens finds they think that a later start time for school and tests given later in the school day would result in better grades. The survey was presented at the American Thoracic Society 2007 International Conference, on Sunday, May 20.

The survey of 280 high school students confirmed what most parents with a teenager know: they are not getting enough sleep. More sleep would translate into improved academic performance, according to the teens questioned. They all attended Harriton High School in suburban Philadelphia, where the school day begins at 7:30 a.m. and ends at 2:25 p.m.

The survey found that:

• 78% of students said it was difficult to get up in the morning
• Only 16% said they regularly had enough sleep
• 70% thought their grades would improve if they had more sleep
• 90% thought their academic performance would improve if school were to start later
  

The surveyed teens say they do not feel alert while taking tests during early morning periods, and they do not think they can perform at the pinnacle of their ability during the early morning hours. Most students said they thought the best time to take a test would be from 11 a.m. to 1 p.m. They thought they would perform better academically and that their grades would improve if they could sleep longer.

Richard Schwab, M.D., of the University of Pennsylvania, conducted the study with his daughter Amanda, one of the sleep-deprived teens who attended Harriton High School. “I watched her get up early for four years, and saw how difficult it was,” Dr. Schwab says. “Teenagers need more sleep than adults and their circadian rhythms are phase shifted so that their ideal bedtime is midnight to 1:00 a.m.; yet they have to get up at 6:30 or earlier for high school.

While adults usually need 7 to 8 hours of sleep, teens need 8 to 9 hours, he says. In addition, teens go to bed much later – their biological clock often keeps them up until 1 a.m. to 2 a.m. Because they have to get up so early for school, many teens achieve only 6 ½ to 7 hours of sleep or, in some cases, much less. That means they tend to sleep in on the weekends, often until 11 am or later, to try to make up for their sleep deficit.

“Right now, high schools usually start earlier in the morning than elementary schools. But if school start times were based on sleep cycles, elementary schools should start at 7:30 and high schools at 8:30 or 8:45 – right now it’s the reverse. School systems should be thinking about changing their start times. It would not be easy—they would have to change the busing system—but it would increase their student's sleep time and likely improve their school performance.”


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