Chapter 10. Biological Rhythms and Sleep
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By Fredrick Kunkle Sleep disturbances such as apnea may increase the risk of Alzheimer’s disease, while moderate exercise in middle age and mentally stimulating games, such as crossword puzzles, may prevent the onset of the dementia-causing disease, according to new research to be presented Monday. The findings — which are to be introduced during the six-day Alzheimer’s Association International Conference in Copenhagen — bolster previous studies that suggest sleep plays a critical role in the aging brain’s health, perhaps by allowing the body to cleanse itself of Alzheimer's-related compounds during down time. The studies also add to a growing body of literature that suggests keeping the brain busy keeps it healthy. The battle against Alzheimer’s disease has become more urgent for the United States and other developing nations as their populations turn increasingly gray. The disease is the leading cause of dementia in older people and afflicts more than 5 million Americans. At its current pace, the number is expected to soar to 16 million people by 2050. In 2012, the United States adopted a national plan to combat the disease and the G-8 nations last year adopted a goal of providing better treatment and prevention by 2025. Erin Heintz, a spokeswoman for the Alzheimer’s Association, said U.S. government funding to combat the disease now stands at about $500 million a year. To reach its 2025 goal, the United States should be spending $2 billion a year, she said.
Carmen Fishwick Do you have difficulty getting enough sleep? Sleep problems affect one in three of us at any one time, and about 10% of the population on a chronic basis. Of Guardian readers who responded to a recent poll, 23% reported that they sleep between four and six hours a night. With continued lack of sufficient sleep, the part of the brain that controls language and memory is severely impaired, and 17 hours of sustained wakefulness is equivalent to performing on a blood alcohol level of 0.05% – the UK's legal drink driving limit. In 2002, American researchers analysed data from more than one million people, and found that getting less than six hours' sleep a night was associated with an early demise – as was getting over eight hours. Studies have found that blood pressure is more than three times greater among those who sleep for less than six hours a night, and women who have less than four hours of sleep are twice as likely to die from heart disease. Other research suggests that a lack of sleep is also related to the onset of diabetes, obesity, and cancer. Are you worried about how much sleep you get? Professor Russell Foster, chair of circadian neuroscience and head of the Sleep and Circadian Neuroscience Institute at the University of Oxford, and professor Colin Espie, professor of sleep medicine at the University of Oxford and lead researcher on the Great British Sleep Survey, answered reader questions. © 2014 Guardian News and Media Limited
Link ID: 19724 - Posted: 06.14.2014
by Moheb Costandi Rest easy after learning a new skill. Experiments in mice suggest that a good night's sleep helps us lay down memories by promoting the growth of new connections between brain cells. Neuroscientists believe that memory involves the modification of synapses, which connect brain cells, and numerous studies published over the past decade have shown that sleep enhances the consolidation of newly formed memories in people. But exactly how these observations were related was unclear. To find out, Wenbiao Gan of the Skirball Institute of Biomolecular Medicine at New York University Medical School and his colleagues trained 15 mice to run backwards or forwards on a rotating rod. They allowed some of them to fall asleep afterwards for 7 hours, while the rest were kept awake. The team monitored the activity and microscopic structure of the mice's motor cortex, the part of the brain that controls movement, through a small transparent "window" in their skulls. This allowed them to watch in real time how the brain responded to learning the different tasks. Sprouting spines They found that learning a new task led to the formation of new dendritic spines – tiny structures that project from the end of nerve cells and help pass electric signals from one neuron to another – but only in the mice left to sleep. This happened during the non-rapid eye movement stage of sleep. Each task caused a different pattern of spines to sprout along the branches of the same motor cortex neurons. © Copyright Reed Business Information Ltd.
Damage to certain parts of the brain can lead to a bizarre syndrome called hemispatial neglect, in which one loses awareness of one side of their body and the space around it. In extreme cases, a patient with hemispatial neglect might eat food from only one side of their plate, dress on only one side of their body, or shave or apply make-up to half of their face, apparently because they cannot pay attention to anything on that the other side. Research published last week now suggests that something like this happens to all of us when we drift off to sleep each night. The work could help researchers to understand the causes of hemispatial neglect, and why it affects one side far more often than the other. It also begins to reveal the profound changes in conscious experience that take place while we fall asleep, and the brain changes that accompany them. Hemispatial neglect is a debilitating condition that occurs often in people who suffer a stroke, where damage to the left hemisphere of the brain results in neglect of the right half of space, and vice versa. It can occur as a result of damage to certain parts of the frontal lobes, which are involved in alertness and attention, and the parietal lobes, which process information about the body and its surrounding space. In clinical tests, patients with hemispatial neglect are typically unaware of all kinds of stimuli in one half of space – they fail to acknowledge objects placed in the affected half of their visual field, for example and cannot state the location of touch sensations on the affected side of their body. Some may stop using the limbs on the affected side, or even deny that the limbs belong to them. Patients with neglect can usually see perfectly well, but information from the affected side just does not reach their conscious awareness. © 2014 Guardian News and Media Limited
By Brady Dennis The Food and Drug Administration is worried that a sleeping pill you take tonight could make for a riskier drive to work tomorrow. In its latest effort to make sure that the millions of Americans taking sleep medications don’t drowsily endanger themselves or others, the agency on Thursday said it will require the manufacturer of the popular drug Lunesta to lower the recommended starting dose, after data showed that people might not be alert enough to drive the morning after taking the drug, even if they feel totally awake. The current recommended starting dose of eszopiclone, the drug marketed as Lunesta, is 2 milligrams at bedtime for both men and women. The FDA said that initial dose should be cut in half to 1 milligram, though it could be increased if needed. People currently taking 2 and 3 milligram doses should ask a doctor about how to safely continue taking the medication, as higher doses are more likely to impair driving and other activities that require alertness the following morning, the agency said. “To help ensure patient safety, health care professionals should prescribe, and patients should take, the lowest dose of a sleep medicine that effectively treats their insomnia,” Ellis Unger, of FDA’s Center for Drug Evaluation and Research, said in a statement. In 2013, the FDA said, approximately 3 million prescriptions of Lunesta were dispensed to nearly a million patients in the United States. Lunesta, made by Sunovion Pharmaceuticals, also recently became available in generic form. The new rules, including changes to existing labels, will apply both to the brand-name and generic forms of the drug. FDA officials said the decision came, in part, after seeing findings from a study of 91 healthy adults between the ages 25 and 40. Compared to patients on a placebo, those taking a 3 milligram dose of Lunesta were associated with “severe next-morning psychomotor and memory impairment in both men and women,” the agency said. The study found that even people taking the recommended dose could suffer from impaired driving skills, memory and coordination as long as 11 hours after taking the drug. Even scarier: The patients often claimed that they felt completely alert, with no hint of drowsiness. © 1996-2014 The Washington Post
Link ID: 19622 - Posted: 05.15.2014
by Helen Thomson If you liked Inception, you're going to love this. People have been given the ability to control their dreams after a quick zap to their head while they sleep. Lucid dreaming is an intriguing state of sleep in which a person becomes aware that they are dreaming. As a result, they gain some element of control over what happens in their dream – for example, the dreamer could make a threatening character disappear or decide to fly to an exotic location. Researchers are interested in lucid dreaming because it can help probe what happens when we switch between conscious states, going from little to full awareness. In 2010, Ursula Voss at the J.W. Goethe University in Frankfurt, Germany, and her colleagues trained volunteers to move their eyes in a specific pattern during a lucid dream. By scanning their brains while they slept, Voss was able to show that lucid dreams coincided with elevated gamma brainwaves. This kind of brainwave occurs when groups of neurons synchronise their activity, firing together about 40 times a second. The gamma waves occurred mainly in areas situated towards the front of the brain, called the frontal and temporal lobes. Perchance to dream The team wanted to see whether gamma brainwaves caused the lucid dreams, or whether both were side effects of some other change. So Voss and her colleagues began another study in which they stimulated the brain of 27 sleeping volunteers, using a non-invasive technique called transcranial alternating current. © Copyright Reed Business Information Ltd.
|By Ariel Van Brummelen The presence of light may do more for us than merely allow for sight. A study by Gilles Vandewalle and his colleagues at the University of Montreal suggests that light affects important brain functions—even in the absence of vision. Previous studies have found that certain photoreceptor cells located in the retina can detect light even in people who do not have the ability to see. Yet most studies suggested that at least 30 minutes of light exposure is needed to significantly affect cognition via these nonvisual pathways. Vandewalle's study, which involved three completely blind participants, found that just a few seconds of light altered brain activity, as long as the brain was engaged in active processing rather than at rest. First the experimenters asked their blind subjects whether a blue light was on or off, and the subjects answered correctly at a rate significantly higher than random chance—even though they confirmed they had no conscious perception of the light. Using functional MRI, the researchers then determined that less than a minute of blue light exposure triggered changes in activity in regions of their brain associated with alertness and executive function. Finally, the scientists found that if the subjects received simultaneous auditory stimulation, a mere two seconds of blue light was enough to modify brain activity. The researchers think the noise engaged active sensory processing, which allowed the brain to respond to the light much more quickly than in previous studies when subjects rested while being exposed to light. The results confirm that the brain can detect light in the absence of working vision. They also suggest that light can quickly alter brain activity through pathways unrelated to sight. The researchers posit that this nonvisual light sensing may aid in regulating many aspects of human brain function, including sleep/wake cycles and threat detection. © 2014 Scientific American,
One of our most mysterious and intriguing states of consciousness is the dream. We lose consciousness when we enter the deep waters of sleep, only to regain it as we emerge into a series of uncanny private realities. These air pockets of inner experience have been difficult for psychologists to study scientifically and, as a result, researchers have mostly resorted to measuring brain activity as the sleeper lies passive. But interest has recently returned to a technique that allows real-time communication from within the dream world. The rabbit hole between these worlds of consciousness turns out to be the lucid dream, where people become aware that they are dreaming and can influence what happens within their self-generated world. Studies suggest that the majority of people have had a lucid dream at some point in their life but that the experience is not common. As a result, there is now a minor industry in technologies and training techniques that claim to increase your chance of having a lucid dream although a recent scientific review estimated that the effect of any particular strategy is moderate at best. Some people, however, can reliably induce lucid dreams and it's these people who are allowing us to conduct experiments inside dreams. When trying to study an experience or behaviour, cognitive scientists usually combine subjective reports, what people describe about their experience, with behavioural experiments, to see what effect a particular state has on how people reason, act or remember. But both are difficult in dreamers, because they can't tell you much until they wake up and active participation in experiments is difficult when you are separated from the world by a blanket of sleep-induced paralysis. This paralysis is caused by neurons in the brainstem that block signals from the action-generating areas in the brain to the spinal nerves and muscles. The shutdown happens when Rapid Eye Movement or REM sleep starts, meaning that dreaming of even the most energetic actions results in no more than a slight twitch. One of the few actions that are not paralysed, however, is eye movement. This is where REM sleep gets its name from and this window of free action provides the lucid dreamer a way of signalling to the outside world. © 2014 Guardian News and Media Limited
Link ID: 19543 - Posted: 04.28.2014
By Ariel Van Brummelen The presence of light may do more for us than merely allow for sight. A study by Gilles Vandewalle and his colleagues at the University of Montreal suggests that light affects important brain functions—even in the absence of vision. Previous studies have found that certain photoreceptor cells located in the retina can detect light even in people who do not have the ability to see. Yet most studies suggested that at least 30 minutes of light exposure is needed to significantly affect cognition via these nonvisual pathways. Vandewalle's study, which involved three completely blind participants, found that just a few seconds of light altered brain activity, as long as the brain was engaged in active processing rather than at rest. First the experimenters asked their blind subjects whether a blue light was on or off, and the subjects answered correctly at a rate significantly higher than random chance—even though they confirmed they had no conscious perception of the light. Using functional MRI, the researchers then determined that less than a minute of blue light exposure triggered changes in activity in regions of their brain associated with alertness and executive function. Finally, the scientists found that if the subjects received simultaneous auditory stimulation, a mere two seconds of blue light was enough to modify brain activity. The researchers think the noise engaged active sensory processing, which allowed the brain to respond to the light much more quickly than in previous studies when subjects rested while being exposed to light. The results confirm that the brain can detect light in the absence of working vision. They also suggest that light can quickly alter brain activity through pathways unrelated to sight. The researchers posit that this nonvisual light sensing may aid in regulating many aspects of human brain function, including sleep/wake cycles and threat detection. © 2014 Scientific American
By Dwayne Godwin and Jorge Cham ABOUT THE AUTHOR(S) Dwayne Godwin is a neuroscientist at the Wake Forest University School of Medicine. Jorge Cham draws the comic strip Piled Higher and Deeper at www.phdcomics.com. © 2014 Scientific American
Link ID: 19473 - Posted: 04.12.2014
by Meghan Rosen Shaking off jet lag could be as easy as downloading an app. Researchers developed the iPhone app, called Entrain, using mathematical analyses of humans’ daily rhythms to calculate the quickest way to adjust to new time zones. Users plug in their destination and arrival time, and Entrain advises times of the day to soak up or stay out of the light. The schedules are surprisingly simple, says mathematical biologist Daniel Forger, of the University of Michigan in Ann Arbor. “They might say, ‘Hey you should keep the lights on in your room until midnight,’” he says. “Or ‘you should stay in darkness until 10 a.m.’” Scientists have previously created mathematical equations that describe how humans’ internal clocks respond to light, Forger says. He and a colleague used a computer program to solve the tricky problem of finding the best lighting schedules for more than 1,000 possible trips. To do so, the researchers asked a question: If a traveler wants to move their body’s clock from New York to London time, for instance, what lighting schedule gets them there fastest? The pair reports the results April 10 in PLOS Computational Biology. K. Serkh and D.B. Forger. Optimal schedules of light exposure for rapidly correcting circadian misalignment. PLOS Computational Biology. Vol.10, April 10, 2014, p. e1003525. Doi: 10.1371/journal.pcbi.1003523. © Society for Science & the Public 2000 - 2013.
Keyword: Biological Rhythms
Link ID: 19472 - Posted: 04.12.2014
By JoNel Aleccia The engineer who drove a speeding commuter train off the rails in New York last year may have suffered from the most severe form of a dangerous sleep disorder, but health experts say he has plenty of company. As many as 22 million people in the U.S. — or up to 7 percent of the population — may suffer from obstructive sleep apnea, experts say. It’s a condition that causes airways to collapse during sleep, cutting off breathing dozens or sometimes hundreds of times a night, leaving them bleary-eyed and drowsy, even after a full night’s rest. William Rockefeller, 46, was diagnosed after the December 2013 crash that killed four and injured more than 70 with severe obstructive sleep apnea, documents released this week show. On a scale where as few as five sleep disruptions an hour can make someone sleepy, and 30 episodes are considered severe, Rockefeller logged about 66 arousals an hour, doctors said. “His sleep was really fragmented,” said Dr. Phyllis Zee, a sleep expert with the Northwestern Medicine Sleep and Circadian Rhythms Research Program. “Even if he were to sleep seven or eight hours, he would be sleep-deprived.” Zee and her colleagues suspected that Rockefeller might suffer from sleep deprivation. He was obese, records show, and there’s a certain fatigued look that she saw in news photos of the engineer. “That was one of my thoughts, ‘Oh my goodness, he has (OSA),’” she said.
Link ID: 19457 - Posted: 04.08.2014
By Helen Briggs BBC News Sleep loss may be more serious than previously thought, causing a permanent loss of brain cells, research suggests. In mice, prolonged lack of sleep led to 25% of certain brain cells dying, according to a study in The Journal of Neuroscience. If the same is true in humans, it may be futile to try to catch up on missed sleep, say US scientists. They think it may one day be possible to develop a drug to protect the brain from the side-effects of lost sleep. The study, published in The Journal of Neuroscience, looked at lab mice that were kept awake to replicate the kind of sleep loss common in modern life, through night shifts or long hours in the office. A team at the University of Pennsylvania School of Medicine studied certain brain cells which are involved in keeping the brain alert. After several days of sleep patterns similar to those followed by night workers - three days of night shifts with only four to five hours sleep in 24 hours - the mice lost 25% of the brain cells, known as locus coeruleus (LC) neurons. The researchers say this is the first evidence that sleep loss can lead to a loss of brain cells. But they add that more work needs to be done to find out if people who miss out on sleep might also be at risk of permanent damage. Prof Sigrid Veasey of the Center for Sleep and Circadian Neurobiology, told BBC News: "We now have evidence that sleep loss can lead to irreversible injury. "This might be in a simple animal but this suggests to us that we are going to have to look very carefully in humans." BBC © 2014
Link ID: 19382 - Posted: 03.19.2014
By Christina Ianzito, We get it: Sleep is good for us. The National Sleep Foundation regularly campaigns “to celebrate the health benefits of sleep,” and experts have been boosting sleep’s values as no less important than proper diet and exercise. Insufficient sleep has been linked to stroke, obesity and heart disease. But sleeping too much may also be risky: It, too, is associated with a higher risk of heart disease and obesity, not to mention diabetes and depression. So, how much is too much? And if you’re sleep-deprived during the week, does sleeping 10 or 11 hours on Saturday and Sunday to catch up put you in any jeopardy? Most experts say that a healthy amount of sleep for an adult is a regular seven to nine hours a night. And the operative term here is “regular,” meaning the issue isn’t the college kid who power-sleeps 15 hours on vacation to catch up from too much studying (or partying). When scientists refer to “long sleepers,” they’re referring to people who consistently sleep nine or more hours a night, says Kristen Knutson, a biomedical anthropologist who focuses on sleep research at the University of Chicago’s Department of Medicine. “If you’ve been pulling all-nighters, by all means extend your sleep on the weekend if you can; try to catch up,” Knutson says, “but if you’re sleeping nine or 10 hours night after night after night for months on end . . . then we’ve got to understand why are you sleeping so much.” You might be getting poor-quality sleep, she adds, or are “already on the pathway to illness and your body is reacting by wanting you to sleep more.” © 1996-2014 The Washington Post
Link ID: 19369 - Posted: 03.17.2014
By JAN HOFFMAN COLUMBIA, Mo. – Jilly Dos Santos really did try to get to school on time. She set three successive alarms on her phone. Skipped breakfast. Hastily applied makeup while her fuming father drove. But last year she rarely made it into the frantic scrum at the doors of Rock Bridge High School here by the first bell, at 7:50 a.m. Then she heard that the school board was about to make the day start even earlier, at 7:20 a.m. “I thought, if that happens, I will die,” recalled Jilly, 17. “I will drop out of school!” That was when the sleep-deprived teenager turned into a sleep activist. She was determined to convince the board of a truth she knew in the core of her tired, lanky body: Teenagers are developmentally driven to be late to bed, late to rise. Could the board realign the first bell with that biological reality? The sputtering, nearly 20-year movement to start high schools later has recently gained momentum in communities like this one, as hundreds of schools in dozens of districts across the country have bowed to the accumulating research on the adolescent body clock. In just the last two years, high schools in Long Beach, Calif.; Stillwater, Okla.; Decatur, Ga.;, and Glens Falls, N.Y., have pushed back their first bells, joining early adopters in Connecticut, North Carolina, Kentucky and Minnesota. The Seattle school board will vote this month on whether to pursue the issue. The superintendent of Montgomery County, Md., supports the shift, and the school board for Fairfax County, Va., is working with consultants to develop options for starts after 8 a.m. © 2014 The New York Times Company
By Pippa Stephens Health reporter, BBC News People are less likely to yawn when others do as they get older, a study has found. Contagious yawning is linked more closely to a person's age than their ability to empathise, as previously thought, US-based scientists said. It also showed a stronger link to age than tiredness or energy levels. Researchers are now looking at whether the ability to catch yawns from other people is inherited, with the hope of helping treat mental health disorders. Autism and schizophrenia sufferers are reportedly less able to catch yawns, researchers said, so understanding the genes that might code for contagious yawning could illuminate new pathways for treatment. In the study, published in the journal Plos One, 328 participants were shown a three-minute video showing other people yawning. Each subject had to click a button every time they yawned. Levels of tiredness Overall, 68% of the participants yawned. Of those, 82% of people aged under 25 yawned, compared with 60% of people aged between 25 and 49, and 41% of people aged over 50. Dr Elizabeth Cirulli, assistant professor of medicine at Duke University in Durham, North Carolina, led the study. She said: "This is the first study to look at a whole bunch of factors. It is the largest study, in terms of the number of people involved, to date." Dr Cirulli said she did not know why contagious yawning decreased with age. BBC © 2014
by Kat Arney Feeling dopey? Refresh your "circadian eye" with a burst of orange light. Light is a powerful wake-up call, enhancing alertness and activity. Its effect is controlled by a group of photoreceptor cells in the eyeball that make the light-sensing pigment melanopsin. These cells, which work separately to the rods and cones needed for vision, are thought to help reset animals' body clocks - or circadian rhythms. Studies with people who are blind suggest this also happens in humans, although the evidence isn't conclusive. To find out how melanopsin wakes up the brain, Gilles Vandewalle at the University of Liege, Belgium, and his team gave 16 people a 10-minute blast of blue or orange light while they performed a memory test in an fMRI scanner. They were then blindfolded for 70 minutes, before being retested under a green light. People initially exposed to orange light had greater brain activity in several regions related to alertness and cognition when they were retested, compared with those pre-exposed to blue light. Light switch Vandewalle thinks that melanopsin is acting as a kind of switch, sending different signals to the brain depending on its state. Orange light, which has the longer wavelength, is known to make the pigment more light-sensitive, but blue light has the opposite effect. Green light lies somewhere in the middle. The findings suggest that pre-exposure to orange light pushes the balance towards the more light-sensitive form of melanopsin, enhancing the response in the brain. © Copyright Reed Business Information Ltd.
by Nathan Seppa MS patients who harbor low levels of vitamin D early in their disease fare worse over the next several years than patients with higher levels. Multiple sclerosis is marked by damage to the fatty sheaths coating nerve fibers in the brain. The result can be an off-and-on series of symptoms including loss of muscle control, numbness and problems thinking. Vitamin D, which the body makes from sun exposure, has shown promise in fighting a variety of diseases and may limit this MS onslaught (SN: 7/16/11, p. 22). In 2002, researchers studying the effect of the drug beta-interferon-1b against MS set aside blood samples from 465 patients. When researchers recently analyzed those samples, they found that patients who had blood levels of vitamin D exceeding 20 nanograms per milliliter at six and 12 months after the onset of MS had fewer symptom flare-ups during the rest of the five-year study than those with lower readings did. Some scientists think 20 nanograms per milliliter is a healthy level; others see 30 as a healthier minimum. MRI scans revealed that, after five years, those who had started out with low vitamin D levels had four times as much myelin damage as those who had higher levels. The results appear in the March JAMA Neurology. A. Ascherio et al. Vitamin D as an early predictor of multiple sclerosis activity and progression. JAMA Neurology. Vol. 71, March 2014, p. 306. doi:10.1001/jamaneurol.2013.5993. © Society for Science & the Public 2000 - 2013
Linda Carroll TODAY contributor Insomnia isn’t something that just happens at night. Researchers have now shown that insomniacs have more active brains than sound sleepers, according to a report published Friday in the journal Sleep. That means sleeplessness may, in fact, have its roots in brain wiring that affects the way our minds work, no matter what time of day it is. “We see insomnia now as more of a 24/7 disorder,” said Dr. Rachel Salas, an assistant professor of neurology at the Johns Hopkins University School of Medicine and lead author of the new study. “It’s like a light switch is continually on. So their brains are always running.” Salas originally thought that sound sleepers would be the ones with more alert and plastic brains. (Brain plasticity basically means how neural pathways can be modified by experience or that it is able to adapt or grow.) To prove the theory, Salas set up an experiment that compared 18 chronic insomniacs to 10 sound sleepers. All of the study volunteers were hooked up to a device that sends magnetic waves through the skull and into the brain. Because transcranial magnetic stimulation (TMS) can be aimed a specific site, the researchers were able to target a point in the motor cortex that controls movements of the thumb. Each magnetic pulse sparked an involuntary twitching of the digit. After 65 run-throughs with the TMS, study volunteers were asked to practice moving their thumbs on their own in a manner opposite to the one that was sparked by the TMS. So, for example, if the TMS sent volunteers’ thumbs flicking up and left, they would be asked to wiggle their digits down and right.
Link ID: 19305 - Posted: 03.01.2014
By Meeri Kim, How often, and how well, do you remember your dreams? Some people seem to be super-dreamers, able to recall effortlessly their dreams in vivid detail almost every day. Others struggle to remember even a vague fragment or two. A new study has discovered that heightened blood flow activity within certain regions of the brain could help explain the great dreamer divide. In general, dream recall is thought to require some amount of wakefulness during the night for the vision to be encoded in longer-term memory. But it is not known what causes some people to wake up more than others. A team of French researchers looked at brain activation maps of sleeping subjects and homed in on areas that could be responsible for nighttime wakefulness. When comparing two groups of dreamers on the opposite ends of the recall spectrum, the maps revealed that the temporoparietal junction — an area responsible for collecting and processing information from the external world — was more highly activated in high-recallers. The researchers speculate that this allows these people to sense environmental noises in the night and wake up momentarily — and, in the process, store dream memories for later recall. In support of this hypothesis, previous medical cases have found that when these same portions of the brain are damaged by stroke, patients lose the ability to remember their dreams, even though they can still achieve the REM (rapid eye movement) stage of sleep in which dreaming usually occurs. © 1996-2014 The Washington Post