Posts tagged wakefulness
Articles and news from the latest research reports.
Quality of waking hours determines ease of falling asleep
The quality of wakefulness affects how quickly a mammal falls asleep, UT Southwestern Medical Center researchers report in a study that identifies two proteins never before linked to alertness and sleep-wake balance.
“This study supports the idea that subjective sleepiness is influenced by the quality of experiences right before bedtime. Are you reluctantly awake or excited to be awake?” said Dr. Masashi Yanagisawa, professor of molecular genetics and a Howard Hughes Medical Institute investigator at UT Southwestern. He is principal author of the study published online in May in the Proceedings of the National Academy of Sciences.
Co-author Dr. Robert Greene, UT Southwestern professor of psychiatry and a physician at the Dallas VA Medical Center, said the study is unique in showing that the need for sleep (called sleep homeostasis) can be separated from wakefulness both behaviorally and biochemically, meaning the two processes can now be studied individually.
“Two of the great mysteries in neuroscience are why do we sleep and what is sleep’s function? Separating sleep need from wakefulness and identifying two different proteins involved in these steps represents a fundamental advance,” he said.
If borne out by further research, this study could lead to new ways of assessing and possibly treating sleep disorders, perhaps by focusing more attention on the hours before bedtime because the quality of wakefulness has a profound effect on sleep, Dr. Yanagisawa said.
The experiment featured three groups of mice with virtually identical genes. The control group slept and woke at will and followed the usual mouse pattern of sleeping during the day and being awake at night. The two test groups were treated the same and had the same amount of sleep delay – six hours – but they were kept awake in different ways, said lead author Dr. Ayako Suzuki, a postdoctoral researcher who works in the laboratories of both Dr. Yanagisawa and Dr. Greene.
The first test group’s sleep was delayed by a series of cage changes. Mice are intensely curious, so each cage change was followed by an hour spent vigorously exploring the new surroundings. This behavior would roughly correspond to teenagers voluntarily delaying bedtime with a new and stimulating event like a rock concert or video game.
Researchers kept the second group awake as gently as possible, usually by waving a hand in front of the cage or tapping it lightly whenever the mice appeared to be settling down to sleep. That test group would more resemble parents reluctantly staying awake awaiting a child’s return from a concert.
Both test groups experienced the same amount of sleep deprivation, but their reactions to the different forms of alertness were striking, Dr. Yanagisawa said. In one test, the cage-changing group took longer to fall asleep than the gentle-handling group even though an analysis of their brain waves indicated equal amounts of sleep need in both test groups.
“The need to sleep is as high in the cage-changing group as in the gentle-handling group, but the cage-changers didn’t feel sleepy at all. Their time to fall asleep was nearly the same as the free-sleeping, well-rested control group,” he said.
The researchers identified two proteins that affected these responses, each linked to different aspects of sleep: phosphorylated dynamin 1 levels were linked to how long it took to fall asleep, while phosphorylated N-myc downstream regulated gene 2 protein levels tracked the amount of sleep deprivation and corresponded to the well-known brain-wave measure of sleep need, they report.
“The two situations are different biochemically, which is a novel finding,” Dr. Yanagisawa said, adding, “These proteins are completely new to sleep research and have never before been linked to sleep need and wakefulness.”
From an evolutionary perspective, an arousal mechanism that adapts to environmental stimuli is crucial because sleeping on a rigid schedule could be dangerous. “Animals, including humans, must be able to keep themselves at least temporarily alert, say during a natural disaster,” he said.
(Image: Robert Manella / Getty Images)
Reactivating memories during sleep
Why do some memories last a lifetime while others disappear quickly?
(Image: Tim Vernon, LTH NHS TRUST/SCIENCE PHOTO LIBRARY)
A new study suggests that memories rehearsed, during either sleep or waking, can have an impact on memory consolidation and on what is remembered later.
The new Northwestern University study shows that when the information that makes up a memory has a high value (associated with, for example, making more money), the memory is more likely to be rehearsed and consolidated during sleep and, thus, be remembered later.
Also, through the use of a direct manipulation of sleep, the research demonstrated a way to encourage the reactivation of low-value memories so they too were remembered later.
Delphine Oudiette, a postdoctoral fellow in the department of psychology at Northwestern and lead author of the study, designed the experiment to study how participants remembered locations of objects on a computer screen. A value assigned to each object informed participants how much money they could make if they remembered it later on the test.
"The pay-off was much higher for some of the objects than for others," explained Ken Paller, professor of psychology at Northwestern and co-author of the study. "In other words, we manipulated the value of the memories — some were valuable memories and others not so much, just as the things we experience each day vary in the extent to which we’d like to be able to remember them later."
When each object was shown, it was accompanied by a characteristic sound. For example, a tea kettle would appear with a whistling sound. During both states of wakefulness and sleep, some of the sounds were played alone, quite softly, essentially reminding participants of the low-value items.
Participants remembered the low-value associations better when the sound presentations occurred during sleep.
"We think that what’s happening during sleep is basically the reactivation of that information," Oudiette said. "We can provoke the reactivation by presenting those sounds, therefore energizing the low-value memories so they get stored better."
The research poses provocative implications about the role memory reactivation during sleep could play in improving memory storage,” said Paller, director of the Cognitive Neuroscience Program at Northwestern. “Whatever makes you rehearse during sleep is going to determine what you remember later, and conversely, what you’re going to forget.”
Many memories that are stored during the day are not remembered.
"We think one of the reasons for that is that we have to rehearse memories in order to keep them. When you practice and rehearse, you increase the likelihood of later remembering," Oudiette said. "And a lot of our rehearsal happens when we don’t even realize it — while we’re asleep."
Paller said selectivity of memory consolidation is not well understood. Most efforts in memory research have focused on what happens when you first form a memory and on what happens when you retrieve a memory.
"The in-between time is what we want to learn more about, because a fascinating aspect of memory storage is that it is not static," Paller said. "Memories in our brain are changing all of the time. Sometimes you improve memory storage by rehearsing all the details, so maybe later you remember better — or maybe worse if you’ve embellished too much.
"The fact that this critical memory reactivation transpires during sleep has mostly been hidden from us, from humanity, because we don’t realize so much of what’s happening while we’re asleep," he said.
(Source: eurekalert.org)
Sleepwalkers sometimes remember what they’ve done
Three myths about sleepwalking – sleepwalkers have no memory of their actions, sleepwalkers’ behaviour is without motivation, and sleepwalking has no daytime impact – are dispelled in a recent study led by Antonio Zadra of the University of Montreal and its affiliated Sacré-Coeur Hospital. Working from numerous studies over the last 15 years at the hospital’s Centre for Advanced Studies in Sleep Medicine at the Hôpital du Sacré-Cœur de Montréal and a thorough analysis of the literature, Zadra and his colleagues have raised the veil on sleepwalking and clarified the diagnostic criteria for researchers and clinicians. Their findings were published in Lancet Neurology.
Question: What are the causes and consequences of sleepwalking?
A.Z.: “Several indicators suggest that a genetic factor is involved. In 80% of sleepwalkers, a family history of sleepwalking exists. The concordance of sleepwalking is five times higher in monozygotic twins compared to non-identical twins. Our studies have also shown that lack of sleep and stress can lead to sleepwalking. Any situation that disrupts sleep can result in sleepwalking episodes in predisposed individuals.”
A.Z.: “Most sleepwalking episodes are harmless. Apart from the fact that the deep slow-wave sleep of sleepwalkers is fragmented, wanderings are usually brief and pose no danger, or when they do, it is minimal. In rare cases, wandering episodes may be longer, and sleepwalkers may injure themselves and put themselves or others in danger: some have even gone as far as driving a car!”
Question: It is said that the sleep disorder mainly affects children. Is this true?
A.Z.: “Many children transitionally sleepwalk between 6 and 12 years of age. It is thought that passing from sleep to wakefulness requires a certain maturation of the brain. In some children, the brain may have difficulty making this transition. Often, the problem disappears after puberty. But sleepwalking may persist into adulthood in almost 25% of cases. It decreases with age, however, because the older you get, the fewer hours of deep slow-wave sleep you enjoy, which is the stage in which sleepwalking episodes occur.”
A.Z.: “Both children and adults are in a state of so-called dissociated arousal during wandering episodes: parts of the brain are asleep while others are awake. There are elements of wakefulness since sleepwalkers can perform actions such as washing, opening and closing doors, or going down stairs. Their eyes are open and they can recognize people. But there are also elements specific to sleep: sleepwalkers’ judgment and their ability for self-thought are altered, and their behavioural reactions are nonsensical.”
Question: According to you, the idea that people are partially awake and partially asleep is something that must be considered in conceptualizing sleepwalking?
A.Z.: “Absolutely. This is one of the points we outline in our article. There are increasing signs that even in normal subjects the brain does not fall asleep in a single block all at once. Sleep may occur in a localized manner. Parts of the brain can fall asleep before others.”
Question: This may explain why the amnesia of sleepwalkers is not always complete. But can sleepwalkers really remember their actions while sleeping vertically?
A.Z.: “Yes. In children and adolescents, amnesia is more frequent, probably due to neurophysiological reasons. In adults, a high proportion of sleepwalkers occasionally remember what they did during their sleepwalking episodes. Some even remember what they were thinking and the emotions they felt.”
Question: Your work has also shown that the behaviour of sleepwalkers is not simply automatic. Can you explain?
A.Z.: “This is another popular myth. There is a misconception that sleepwalkers do things without knowing why. However, there is a significant proportion of sleepwalkers who remember what they have done and can explain the reasons for their actions. They are the first to say, once awake, that their explanations are nonsensical. However, during the episode, there is an underlying rationale. For example, a man once took his dog that had been sleeping at the foot of his bed to the bathtub to douse it with water. He thought his dog was on fire! There was neither the logic nor the judgment typical of wakefulness. But the behaviour was not automatic in the sense that a motivation accompanied and explained the action.”
Question: Another myth you are interested in relates to impact on the waking state. According to you, beyond the nocturnal phenomenon, sleepwalking is associated with diurnal disorders characterized by somnolence.
A.Z.: “Around 45% of sleepwalkers are clinically somnolent during the day. Younger sleepwalkers are able to hide it more easily. Compared to control subjects, however, they perform less well in vigilance tests. And if given the opportunity to take a nap, they fall asleep faster than normal subjects do.”
A.Z.: “Over the last few years, we have shown that the deep slow-wave sleep of sleepwalkers is atypical. Fragmented by numerous micro-arousals of 3 to 10 seconds, their sleep is less restorative. Sleepwalking is therefore not only a problem of transitioning between deep sleep and wakefulness. There is something more fundamental in their sleep every night, whether or not they have sleepwalking episodes.”
Previously unknown sleep pattern revealed in University of Sydney research
There’s no need to panic if you didn’t get a solid eight hours of beauty sleep last night. According to new University of Sydney research, sleep duration naturally waxes and wanes over a period of days regardless of individual lifestyle, timing of sleep or waking, and social and environmental influences.
With further research, the discovery could have important implications for predicting work performance, managing fatigue-related accidents after shift work, and treatment recovery in clinical populations.
"Sleep requirements vary in a cyclical fashion and between individuals. If you incur a sleep debt, your body will signal a need to catch up on extra sleep," says Dr Chin Moi Chow, principal investigator of the article published in Nature and Science of Sleep.
"As you increase your sleep duration to recover from the debt, your ability to prolong wakefulness increases. Then, as prior wakefulness increases, sleepiness is inevitable, and a need for further sleep develops again."
Dr Chow and colleagues Shi Wong and Dr Mark Halaki, from the University’s Faculty of Health Sciences, monitored a group of healthy young males over a fortnight using an actigraph - a small activity recording device worn like a wristwatch on the non-dominant arm - designed to measure sleep patterns.
To the researchers’ fascination, the actigraph data showed participants’ sleep duration oscillated in a sine wave pattern - a phenomenon that had not previously been observed. Clear periodic patterns were found in the majority of the participants, varying from periods of between two and 18 days.
The cyclic pattern observed in the research suggests that the sleep balance mechanism operates on an ongoing basis in daily life, with changes in sleep duration constantly accompanied by compensatory adjustments.
Interestingly, despite the fact that participants in the study habitually slept below the recommended seven to eight hours a night, they still maintained a cyclic sleep duration pattern.
"Our sleep quantity and quality vary according to a range of factors," Dr Chow says. "Some individuals have a slower accumulation or faster dissipation of sleep pressure, which may define their pattern of total sleep time."
Variations in daily sleep duration may also arise from differences such as slight variations in the body clock or external factors like temperature, daylight, exercise, or eating and drinking patterns.
"Changing your sleep patterns on weekends, or resetting the pattern through shift work, could alter your sleep duration cycle and could put the body under significant strain," says Dr Chow.
This research is part of Dr Chow’s broader interest in the lifestyle factors influencing sleep. The team hopes to follow the research by examining the cyclical phenomenon in special groups such as long or short sleepers and people with insomnia.