Tag: sleep

Categories : EndocrinologyTags :

Sleep and Growth Hormones Tightly Regulate One Another

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As every bodybuilder knows, a deep, restful sleep boosts levels of growth hormone to build strong muscle and bone and burn fat. And as every teenager should know, they won’t reach their full height potential without adequate growth hormone from a full night’s sleep.

But why lack of sleep – in particular the early, deep phase called non-REM sleep — lowers levels of growth hormone has been a mystery.

In a study published in the current issue of the journal Cell, researchers from University of California, Berkeley, dissect the brain circuits in mice that control growth hormone release during sleep and report a novel feedback mechanism in the brain that keeps growth hormone levels finely balanced.

The findings provide a map for understanding how sleep and hormone regulation interact. The new feedback mechanism could open avenues for treating people with sleep disorders tied to metabolic conditions like diabetes, as well as degenerative diseases like Parkinson’s and Alzheimer’s.

“People know that growth hormone release is tightly related to sleep, but only through drawing blood and checking growth hormone levels during sleep,” said study first author Xinlu Ding, a postdoctoral fellow in UC Berkeley’s Department of Neuroscience and the Helen Wills Neuroscience Institute. “We’re actually directly recording neural activity in mice to see what’s going on. We are providing a basic circuit to work on in the future to develop different treatments.”

Because growth hormone regulates glucose and fat metabolism, insufficient sleep can also worsen risks for obesity, diabetes and cardiovascular disease.

The sleep-wake cycle

The neurons that orchestrate growth hormone release during the sleep-wake cycle – growth hormone releasing hormone (GHRH) neurons and two types of somatostatin neurons – are buried deep in the hypothalamus, an ancient brain hub conserved in all mammals. Once released, growth hormone increases the activity of neurons in the locus coeruleus, an area in the brainstem involved in arousal, attention, cognition and novelty seeking. Dysregulation of locus coeruleus neurons is implicated in numerous psychiatric and neurological disorders.

“Understanding the neural circuit for growth hormone release could eventually point toward new hormonal therapies to improve sleep quality or restore normal growth hormone balance,” said Daniel Silverman, a UC Berkeley postdoctoral fellow and study co-author. “There are some experimental gene therapies where you target a specific cell type. This circuit could be a novel handle to try to dial back the excitability of the locus coeruleus, which hasn’t been talked about before.”

The researchers, working in the lab of Yang Dan, a professor of neuroscience and of molecular and cell biology, explored the neuroendocrine circuit by inserting electrodes in the brains of mice and measuring changes in activity after stimulating neurons in the hypothalamus with light. Mice sleep for short periods – several minutes at a time – throughout the day and night, providing many opportunities to study growth hormone changes during sleep-wake cycles.

Using state-of-the-art circuit tracing, the team found that the two small-peptide hormones that control the release of growth hormone in the brain – GHRH, which promotes release, and somatostatin, which inhibits release – operate differently during REM and non-REM sleep. Somatostatin and GHRH surge during REM sleep to boost growth hormone, but somatostatin decreases and GHRH increases only moderately during non-REM sleep to boost growth hormone.

Released growth hormone regulates locus coeruleus activity, as a feedback mechanism to help create a homeostatic yin-yang effect. During sleep, growth hormone slowly accumulates to stimulate the locus coeruleus and promote wakefulness, the new study found. But when the locus coeruleus becomes overexcited, it paradoxically promotes sleepiness, as Silverman showed in a study published earlier this year.

“This suggests that sleep and growth hormone form a tightly balanced system: Too little sleep reduces growth hormone release, and too much growth hormone can in turn push the brain toward wakefulness,” Silverman said. “Sleep drives growth hormone release, and growth hormone feeds back to regulate wakefulness, and this balance is essential for growth, repair and metabolic health.”

Because growth hormone acts in part through the locus coeruleus, which governs overall brain arousal during wakefulness, a proper balance could have a broader impact on attention and thinking.

“Growth hormone not only helps you build your muscle and bones and reduce your fat tissue, but may also have cognitive benefits, promoting your overall arousal level when you wake up,” Ding said.

Source: University of California – Berkeley

Categories : NeurologyTags :

How ‘Brain Cleaning’ While We Sleep May Lower Our Risk of Dementia

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Julia Chapman, Macquarie University; Camilla Hoyos, Macquarie University, and Craig Phillips, Macquarie University

The brain has its own waste disposal system – known as the glymphatic system – that’s thought to be more active when we sleep.

But disrupted sleep might hinder this waste disposal system and slow the clearance of waste products or toxins from the brain. And researchers are proposing a build-up of these toxins due to lost sleep could increase someone’s risk of dementia.

There is still some debate about how this glymphatic system works in humans, with most research so far in mice.

But it raises the possibility that better sleep might boost clearance of these toxins from the human brain and so reduce the risk of dementia.

Here’s what we know so far about this emerging area of research.

Why waste matters

All cells in the body create waste. Outside the brain, the lymphatic system carries this waste from the spaces between cells to the blood via a network of lymphatic vessels.

But the brain has no lymphatic vessels. And until about 12 years ago, how the brain clears its waste was a mystery. That’s when scientists discovered the “glymphatic system” and described how it “flushes out” brain toxins.

Let’s start with cerebrospinal fluid, the fluid that surrounds the brain and spinal cord. This fluid flows in the areas surrounding the brain’s blood vessels. It then enters the spaces between the brain cells, collecting waste, then carries it out of the brain via large draining veins.

Scientists then showed in mice that this glymphatic system was most active – with increased flushing of waste products – during sleep.

One such waste product is amyloid beta (Aβ) protein. Aβ that accumulates in the brain can form clumps called plaques. These, along with tangles of tau protein found in neurons (brain cells), are a hallmark of Alzheimer’s disease, the most common type of dementia.

In humans and mice, studies have shown that levels of Aβ detected in the cerebrospinal fluid increase when awake and then rapidly fall during sleep.

But more recently, another study (in mice) showed pretty much the opposite – suggesting the glymphatic system is more active in the daytime. Researchers are debating what might explain the findings.

So we still have some way to go before we can say exactly how the glymphatic system works – in mice or humans – to clear the brain of toxins that might otherwise increase the risk of dementia.

Does this happen in humans too?

We know sleeping well is good for us, particularly our brain health. We are all aware of the short-term effects of sleep deprivation on our brain’s ability to function, and we know sleep helps improve memory.

In one experiment, a single night of complete sleep deprivation in healthy adults increased the amount of Aβ in the hippocampus, an area of the brain implicated in Alzheimer’s disease. This suggests sleep can influence the clearance of Aβ from the human brain, supporting the idea that the human glymphatic system is more active while we sleep.

This also raises the question of whether good sleep might lead to better clearance of toxins such as Aβ from the brain, and so be a potential target to prevent dementia.

How about sleep apnoea or insomnia?

What is less clear is what long-term disrupted sleep, for instance if someone has a sleep disorder, means for the body’s ability to clear Aβ from the brain.

Sleep apnoea is a common sleep disorder when someone’s breathing stops multiple times as they sleep. This can lead to chronic (long-term) sleep deprivation, and reduced oxygen in the blood. Both may be implicated in the accumulation of toxins in the brain.

Sleep apnoea has also been linked with an increased risk of dementia. And we now know that after people are treated for sleep apnoea more Aβ is cleared from the brain.

Insomnia is when someone has difficulty falling asleep and/or staying asleep. When this happens in the long term, there’s also an increased risk of dementia. However, we don’t know the effect of treating insomnia on toxins associated with dementia.

So again, it’s still too early to say for sure that treating a sleep disorder reduces your risk of dementia because of reduced levels of toxins in the brain.

So where does this leave us?

Collectively, these studies suggest enough good quality sleep is important for a healthy brain, and in particular for clearing toxins associated with dementia from the brain.

But we still don’t know if treating a sleep disorder or improving sleep more broadly affects the brain’s ability to remove toxins, and whether this reduces the risk of dementia. It’s an area researchers, including us, are actively working on.

For instance, we’re investigating the concentration of Aβ and tau measured in blood across the 24-hour sleep-wake cycle in people with sleep apnoea, on and off treatment, to better understand how sleep apnoea affects brain cleaning.

Researchers are also looking into the potential for treating insomnia with a class of drugs known as orexin receptor antagonists to see if this affects the clearance of Aβ from the brain.

If you’re concerned

This is an emerging field and we don’t yet have all the answers about the link between disrupted sleep and dementia, or whether better sleep can boost the glymphatic system and so prevent cognitive decline.

So if you are concerned about your sleep or cognition, please see your doctor.

Julia Chapman, Clinical Trials Lead and Postdoctoral Research Fellow, Woolcock Institute of Medical Research and Conjoint Lecturer, Macquarie University; Camilla Hoyos, Senior Lecturer in the Centre for Sleep and Chronobiology, Macquarie University, and Craig Phillips, Associate Professor, Macquarie Medical School, Macquarie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Categories : Mental HealthTags :

Good Sleep Quality Might be Key for Better Mental Wellbeing in Young Adults

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Study also suggests eating fruit and vegetables and exercising are linked with strong benefits – and fruit and vegetable consumption might compensate for poor sleep

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A new study of young adults has strongly linked better sleep quality with better mental wellbeing, with fruit and vegetable consumption and physical activity also strongly associated with psychological wellbeing. Perhaps surprisingly, the findings also suggest that boosting fruit and vegetable intake could potentially help mitigate the effects on wellbeing of a poor night’s sleep. Dr Jack Cooper, previously from the University of Otago, New Zealand, and colleagues present these findings in the open-access journal PLOS One on August 27, 2025.

Prior research has linked better health behaviours—actions that people can adjust in their lives—to better physical health. Evidence also suggests that health behaviours may be linked to mental wellbeing. However, research on this topic has been limited. For example, studies have typically focused only on mental illness, a separate measure from positive psychological wellbeing, and they typically neglect to consider how different health behaviours might interact to affect wellbeing.

To address these and other gaps, Cooper and colleagues analysed relationships between three health behaviours – sleep quality, eating fruits and vegetables, and physical activity – and psychological wellbeing in adults aged 17 to 25. They used data from three studies: a survey study of 1032 adults in New Zealand, the UK, and the US; a 13-day study of 818 New Zealand adults who were asked to keep a daily diary; and an 8-day diary study of 236 New Zealand adults who also wore Fitbits tracking physical activity.

Across all three studies, better sleep quality was most strongly associated with better mental wellbeing, with fruit and vegetable consumption coming in second. Both behaviours showed benefits even when comparing between different days for the same person – so eating more fruit and vegetables one day was associated with a real-time wellbeing boost. Physical activity – whether measured by FitBits or diaries, which aligned – was also linked to better wellbeing, but mostly when comparing between days for an individual rather than when comparing across individuals.

Links between each of the three behaviors and wellbeing appeared to be independent and additive – which might mean that the more of them you do, the bigger the wellbeing benefit. The only exception: above-average intake of fruits and vegetables appeared to mitigate the effects of a poor night’s sleep, and a good night’s sleep appeared to protect against lower fruit and vegetable intake.

This study used samples of young adults from three countries—the U.K., U.S., and New Zealand—and samples sizes were relatively homogeneous. Future research could address some of these limitations by including participants from additional countries and increasing the sample size to improve generalizability. Although this study could not prove a causative link between these behaviors and mental wellbeing, the authors hope that their findings could inform efforts to improve psychological wellbeing of young adults.

Lead author Dr. Jack Cooper adds: “Young adults don’t have to reach some objective benchmark of healthiness to see wellbeing improvement. Sleeping a little better, eating a little healthier, or exercising even for 10 minutes longer than you normally do was associated with improvements to how you feel that day.”

Senior author Professor Tamlin Conner, of the University of Otago Psychology Department, adds: “Understanding what lifestyle factors support wellbeing can help young adults not just ‘get by’ but thrive during this critical life stage.”

“Of these healthy habits, sleep quality stood out as the strongest and most consistent predictor of next-day wellbeing, but eating fruit and vegetables and being active also helped boost wellbeing”.

“This age group faces unique pressures – such as leaving home, financial stress, educational pressures and social stressors – that can lower happiness. Understanding what lifestyle factors support wellbeing can help young adults not just ‘get by’ but thrive during this critical life stage.

Provided by PLOS

Categories : Mental HealthTags :

Insomnia Patients Report Better Sleep when Taking Cannabis-based Medical Products

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Patients reported better sleep as well as decreased anxiety and pain over 18 months of treatment 

Insomnia patients taking cannabis-based medical products reported better quality sleep after up to 18 months of treatment, according to a study published August 27 in the open-access journal PLOS Mental Health by Arushika Aggarwal from Imperial College London, U.K., and colleagues.

About one out of every three people has some trouble getting a good night’s rest, and 10% of adults meet the criteria for an insomnia disorder. But current treatments can be difficult to obtain, and the drugs approved for insomnia run the risk of dependence. To understand how cannabis-based medical products might affect insomnia symptoms, the authors of this study analysed a set of 124 insomnia patients taking medical cannabis products. They examined the patient’s reports of their sleep quality, anxiety/depression, and quality of life changes between one and 18 months of treatment.

The patients reported improved sleep quality that lasted over the 18 months of treatment. They also showed significant improvements in anxiety/depression as well as reporting less pain. About 9% of the patients reported adverse effects such as fatigue, insomnia, or dry mouth, but none of the side effects were life-threatening. While randomised controlled trials will be needed to prove that the products are safe and effective, the authors suggest that cannabis-based medical products could improve sleep quality in insomnia patients.

Co-author Dr Simon Erridge, Research Director at Curaleaf Clinic, summarises: “Over an 18-month period, our study showed that treatment for insomnia with cannabis-based medicinal products was associated with sustained improvements in subjective sleep quality and anxiety symptoms. These findings support the potential role of medical cannabis as a medical option where conventional treatments have proven ineffective, though further randomised trials are needed to confirm long-term efficacy.”

He adds: “Conducting this long-term study provided valuable real-world evidence on patient outcomes that go beyond what we typically see in short-term trials. It was particularly interesting to observe signs of potential tolerance over time, which highlights the importance of continued monitoring and individualised treatment plans.”

Provided by PLOS

Categories : Cardiovascular DiseaseTags :

Regular Sleep Schedule May Improve Recovery from Heart Failure Hospitalisation

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People recovering from heart failure should consider improving the regularity of their sleep, a study led by Oregon Health & Science University suggests. The research team found that even moderately irregular sleep doubles the risk of having another clinical event within six months, according to a study published in the journal JACC Advances. A clinical event could be another visit to the emergency room, hospitalisation or even death.

“Going to bed and waking up at consistent times is important for overall health,” said lead author Brooke Shafer, PhD, a research assistant professor in the Sleep, Chronobiology and Health Laboratory in the OHSU School of Nursing. “Our study suggests that consistency in sleep timing may be especially important for adults with heart failure.”

Researchers enrolled 32 patients who had been hospitalised for acutely decompensated heart failure at OHSU Hospital and Hillsboro Medical Center from September 2022 through October 2023. For one week following hospital discharge, participants used sleep diaries to record the time they fell asleep at night, woke up in the morning and the timing of naps they took during the day.

The participants were then categorised as regular sleepers or moderately irregular sleepers, based on their sleep patterns.

The study found:

  • Following discharge from the hospital, 21 participants experienced a clinical event over the course of six months.
  • Of that group, 13 were classified as moderately irregular sleepers compared with eight classified as having a regular sleep schedule.
  • Statistically, the irregular sleepers had more than double the risk of an event across the six-month time span.

The increased risk of a clinical event for moderately irregular sleepers remained even when accounting for possible contributing factors like sleep disorders and other underlying medical conditions. The research team says the study is among the first to examine the impact of sleep regularity in the context of heart failure, and the findings add to a growing body of evidence suggesting the importance of maintaining a regular sleep schedule.

“Improving sleep regularity may be a low-cost therapeutic approach to mitigate adverse events in adults with heart failure,” the authors conclude.

Shafer said the results strengthen the connection between sleep regularity and cardiovascular health.

“When we’re asleep and in a resting state, our blood pressure and heart rate decrease compared with daytime levels,” she said. “But variability in sleep timing may disrupt mechanisms involved in the regulation of the cardiovascular system. Irregular sleep may contribute to adverse outcomes, especially for people already affected by heart failure.”

The next step would be to scale up the research to a larger cohort of participants and see whether improving sleep regularity lowers the risk of another clinical event, she said.

Source: Oregon Health & Science University

Categories : NeurologyTags :

Why Do We Need Sleep? Oxford Researchers Find the Answer May Lie in Mitochondria

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New study uncovers how a metabolic “overload” in specialised brain cells triggers the need to sleep.

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Sleep may not just be rest for the mind – it may be essential maintenance for the body’s power supply. A new study by University of Oxford researchers, published in Nature, reveals that the pressure to sleep arises from a build-up of electrical stress in the tiny energy generators inside brain cells.

The discovery offers a physical explanation for the biological drive to sleep and could reshape how scientists think about sleep, ageing, and neurological disease.

Led by Professor Gero Miesenböck from the Department of Physiology, Anatomy and Genetics (DPAG), and Dr Raffaele Sarnataro at Oxford’s Centre for Neural Circuits and Behaviour, the team found that sleep is triggered by the brain’s response to a subtle form of energy imbalance. The key lies in mitochondria – microscopic structures inside cells that use oxygen to convert food into energy.

When the mitochondria of certain sleep-regulating brain cells (studied in fruit flies) become overcharged, they start to leak electrons, producing potentially damaging byproducts known as reactive oxygen species. This leak appears to act as a warning signal that pushes the brain into sleep, restoring equilibrium before damage spreads more widely.

‘You don’t want your mitochondria to leak too many electrons,’ said Dr Sarnataro. ‘When they do, they generate reactive molecules that damage cells.’

The researchers found that specialised neurons act like circuit breakers – measuring this mitochondrial electron leak and triggering sleep when a threshold is crossed. By manipulating the energy handling in these cells – either increasing or decreasing electron flow – the scientists could directly control how much the flies slept.

Even replacing electrons with energy from light (using proteins borrowed from microorganisms) had the same effect: more energy, more leak, more sleep.

Professor Miesenböck said: ‘We set out to understand what sleep is for, and why we feel the need to sleep at all. Despite decades of research, no one had identified a clear physical trigger. Our findings show that the answer may lie in the very process that fuels our bodies: aerobic metabolism. In certain sleep-regulating neurons, we discovered that mitochondria – the cell’s energy producers – leak electrons when there is an oversupply. When the leak becomes too large, these cells act like circuit breakers, tripping the system into sleep to prevent overload.’

The findings help explain well-known links between metabolism, sleep, and lifespan. Smaller animals, which consume more oxygen per gram of body weight, tend to sleep more and live shorter lives. Humans with mitochondrial diseases often experience debilitating fatigue even without exertion, now potentially explained by the same mechanism.

‘This research answers one of biology’s big mysteries,’ said Dr Sarnataro.

‘Why do we need sleep? The answer appears to be written into the very way our cells convert oxygen into energy.’

The paper, ‘Mitochondrial origins of the pressure to sleep‘, is published in Nature.

Source: University of Oxford

Categories : ExerciseTags :

An Early Night is Linked to More Physical Activity than Burning the Midnight Oil

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Going to bed earlier than usual may help to optimise physical activity the following day, Monash University-led research has found.

Published in Proceedings of the National Academy of Sciences (PNAS), the study examined whether sleep duration and sleep timing were associated with the duration of moderate-to-vigorous and overall physical activity the following day.

In the primary study, almost 20 000 participants wore a validated biometric device (WHOOP) for one year, resulting in almost six million nights of data. Objective sleep and physical activity metrics were derived from the wrist-worn device.

The study examined how both typical sleep habits and nightly fluctuations in sleep were linked to next-day physical activity levels.

On average, people who went to bed earlier were more physically active. For example, those with a typical bedtime around 9pm logged about 30 more minutes of moderate-to-vigorous physical activity each day compared to those who regularly stayed up until 1am.

Even compared to those who typically went to bed at 11pm (the average bedtime for the entire sample), the 9pm sleepers recorded nearly 15 additional minutes of daily moderate-to-vigorous physical activity.

Lead author Dr Josh Leota, from Monash University’s School of Psychological Sciences, said the findings suggested individuals with later bedtimes may be at a disadvantage under conventional work schedules.

“Standard 9-to-5 routines can clash with the natural sleep preferences of evening types, leading to social jetlag, poorer sleep quality, and increased daytime sleepiness – which can all reduce motivation and opportunity for physical activity the next day,” Dr Leota said.

Importantly, the study also looked at whether individuals can actively alter this relationship. The researchers found that when people went to sleep earlier than usual but still got their typical amount of sleep, they recorded the highest levels of physical activity the next day.

“These insights carry meaningful implications for public health,” Dr Leota said. “Rather than just promoting sleep and physical activity independently, health campaigns could encourage earlier bedtimes to naturally foster more active lifestyles. A holistic approach that recognises how these two essential behaviours interact may lead to better outcomes for individual and community health.”

An additional validation study involving almost 6000 participants from the All of Us Research Program, using Fitbit data, reinforced these findings, showing the relationships were broadly consistent across diverse populations.

Senior author Dr Elise Facer-Childs, from the Monash University School of Psychological Sciences, said that these findings highlight a powerful relationship between sleep timing and physical activity.

“Sleep and physical activity are both critical to health, but until now we didn’t fully grasp how intricately connected they are in everyday life,” Dr Facer-Childs said.

“Our findings are consistent across different populations, and show that if you can get to sleep earlier than usual whilst keeping your sleep duration the same, you may be more likely to increase your physical activity the following day”, says Dr Facer-Childs.

Read the research paper here: DOI 10.1073/pnas.2420846122

Source: Monash University

Categories : UncategorizedTags :

Adolescents Who Sleep Longer Perform Better at Cognitive Tasks

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Adolescents who sleep for longer – and from an earlier bedtime – than their peers tend to have improved brain function and perform better at cognitive tests, researchers from the UK and China have shown.

But the study of adolescents in the US also showed that even those with better sleeping habits were not reaching the amount of sleep recommended for their age group.

Sleep plays an important role in helping our bodies function. It is thought that while we are asleep, toxins that have built up in our brains are cleared out, and brain connections are consolidated and pruned, enhancing memory, learning, and problem-solving skills. Sleep has also been shown to boost our immune systems and improve our mental health.

During adolescence, our sleep patterns change. We tend to start going to bed later and sleeping less, which affects our body clocks. All of this coincides with a period of important development in our brain function and cognitive development. The American Academy of Sleep Medicine says that the ideal amount of sleep during this period is between eight- and 10-hours’ sleep.

Professor Barbara Sahakian from the Department of Psychiatry at the University of Cambridge said: “Regularly getting a good night’s sleep is important in helping us function properly, but while we know a lot about sleep in adulthood and later life, we know surprisingly little about sleep in adolescence, even though this is a crucial time in our development. How long do young people sleep for, for example, and what impact does this have on their brain function and cognitive performance?”

Studies looking at how much sleep adolescents get usually rely on self-reporting, which can be inaccurate. To get around this, a team led by researchers at Fudan University, Shanghai, and the University of Cambridge turned to data from the Adolescent Brain Cognitive Development (ABCD) Study, the largest long-term study of brain development and child health in the United States.

As part of the ABCD Study, more than 3200 adolescents aged 11-12 years old had been given FitBits, allowing the researchers to look at objective data on their sleep patterns and to compare it against brain scans and results from cognitive tests. The team double-checked their results against two additional groups of 13-14 years old, totalling around 1190 participants. The results are published today in Cell Reports.

The team found that the adolescents could be divided broadly into one of three groups:

Group One, accounting for around 39% of participants, slept an average (mean) of 7 hours 10 mins. They tended to go to bed and fall asleep the latest and wake up the earliest.

Group Two, accounting for 24% of participants, slept an average of 7 hours 21 mins. They had average levels across all sleep characteristics.

Group Three, accounting for 37% of participants, slept an average of 7 hours 25 mins. They tended to go to bed and fall asleep the earliest and had lower heart rates during sleep.

Although the researchers found no significant differences in school achievement between the groups, when it came to cognitive tests looking at aspects such as vocabulary, reading, problem solving and focus, Group Three performed better than Group Two, which in turn performed better than Group One.

Group Three also had the largest brain volume and best brain functions, with Group One the smallest volume and poorest brain functions.

Professor Sahakian said: “Even though the differences in the amount of sleep that each group got was relatively small, at just over a quarter-of-an-hour between the best and worst sleepers, we could still see differences in brain structure and activity and in how well they did at tasks. This drives home to us just how important it is to have a good night’s sleep at this important time in life.”

First author Dr Qing Ma from Fudan University said: “Although our study can’t answer conclusively whether young people have better brain function and perform better at tests because they sleep better, there are a number of studies that would support this idea. For example, research has shown the benefits of sleep on memory, especially on memory consolidation, which is important for learning.”

The researchers also assessed the participants’ heart rates, finding that Group Three had the lowest heart rates across the sleep states and Group One the highest. Lower heart rates are usually a sign of better health, whereas higher rates often accompany poor sleep quality like restless sleep, frequent awakenings and excessive daytime sleepiness.

Because the ABCD Study is a longitudinal study – that is, one that follows its participants over time – the team was able to show that the differences in sleep patterns, brain structure and function, and cognitive performance, tended be present two years before and two years after the snapshot that they looked at.

Senior author Dr Wei Cheng from Fudan University added: “Given the importance of sleep, we now need to look at why some children go to bed later and sleep less than others. Is it because of playing videogames or smartphones, for example, or is it just that their body clocks do not tell them it’s time to sleep until later?”

The research was supported by the National Key R&D Program of China, National Natural Science Foundation of China, National Postdoctoral Foundation of China and Shanghai Postdoctoral Excellence Program. The ABCD Study is supported by the National Institutes of Health.

Reference

Ma, Q et al. Neural correlates of device-based sleep characteristics in adolescents. Cell Reports; 22 Apr 2025; DOI: 10.1016/j.celrep.2025.115565


Republished under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Read the original article.

Categories : Neurology OphthalmologyTags :

The Pupil as a Window into the Sleeping Brain

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The eye of the sleeping subject was kept open with a special fixation device to record the pupil movements for several hours.  (Image: Neural Control of Movement Lab / ETH Zurich)

For the first time, researchers have been able to observe how the pupils react during sleep over a period of several hours. A look under the eyelids showed them that more happens in the brain during sleep than was previously assumed.

While eyes are typically closed in sleep, there is a flurry of activity taking place beneath the eyelids: a team of researchers, led by principal investigators Caroline Lustenberger, Sarah Meissner and Nicole Wenderoth from the Neural Control of Movement Lab at ETH Zurich, have observed that the size of the pupil fluctuates constantly during sleep. As they report in Nature Communications, sometimes it increases in size, sometimes it decreases; sometimes these changes occur within seconds, other times over the course of several minutes.

“These dynamics reflect the state of arousal, or the level of brain activation in regions that are responsible for sleep-wake regulation,” says Lustenberger. “These observations contradict the previous assumption that, essentially, the level of arousal during sleep is low.”

Instead, these fluctuations in pupil size show that even during sleep, the brain is constantly switching between a higher and lower level of activation. These new findings also confirm for humans what other research groups have recently discovered in studies on rodents, who also exhibit slow fluctuations in the activation level (known in the field as arousal).

New method for an old mystery

The regions of the brain which control the activation level are situated deep within the brainstem, making it previously difficult to directly measure these processes in humans during sleep. Existing methods are technically demanding and have not yet been established in this context. The ETH researchers’ study therefore relies on pupil measurements. Pupils are known to indicate the activation level when a person is awake. They can therefore be used as markers for the activity in regions situated deeper within the brain.

The ETH researchers developed a new method for examining the changes in people’s pupils while asleep: using a special adhesive technique and a transparent plaster, they were able to keep the eyes of the test subjects open for several hours.

“Our main concern was that the test subjects would be unable to sleep with their eyes open. But in a dark room, most people forget that their eyes are still open and they are able to sleep,” explains the study’s lead author, Manuel Carro Domínguez, who developed the technique.

Analysis of the data showed that pupil dynamics is related not just to the different stages of sleep, but also to specific patterns of brain activity, such as sleep spindles and pronounced deep sleep waves – brain waves that are important for memory consolidation and sleep stability. The researchers also discovered that the brain reacts to sounds with varying degrees of intensity, depending on the level of activation, which is reflected in the size of the pupil.

A central regulator of the activation level is a small region in the brainstem, known as the locus coeruleus. In animals, scientists have been able to show that this is important for the regulation of sleep stages and waking. The ETH researchers were unable to prove in this study whether the locus coeruleus is indeed directly responsible for pupil changes. “We are simply observing pupil changes that are related to the level of brain activation and heart activity,” Lustenberger explains.

In a follow-up study, the researchers will attempt to influence the activity of the locus coeruleus using medication, so that they can investigate how this affects pupil dynamics. They hope to discover whether this region of the brain is in fact responsible for controlling the pupils during sleep, and how changes in the level of activation affect sleep and its functions.

Using pupillary dynamics to diagnose illnesses

Understanding pupil dynamics during sleep could also provide important insights for the diagnosis and treatment of sleep disorders and other illnesses. The researchers therefore want to investigate whether pupil changes during sleep can provide indications of dysfunctions of the arousal system. These include disorders such as insomnia, post-traumatic stress disorder and possibly Alzheimer’s. “These are just hypotheses that we want to investigate in the future,” says Lustenberger.

Another goal is to make the technology usable outside of sleep laboratories, such as in hospitals where it could help to monitor waking in coma patients or to diagnose sleep disorders more accurately. The pupil as a window onto the brain could thus pave the way for new opportunities in sleep medicine and neuroscience.

Source: ETH Zurich

Categories : NeurologyTags :

New Insights into Sleep Uncover Mechanism for Enhancing Cognitive Function

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While it’s well known that sleep enhances cognitive performance, the underlying neural mechanisms, particularly those related to nonrapid eye movement (NREM) sleep, remain largely unexplored. A new study by a team of researchers coordinated by Rice University’s Valentin Dragoi, has nonetheless uncovered a key mechanism by which sleep enhances neuronal and behavioural performance, potentially changing our fundamental understanding of how sleep boosts brainpower.

The research, published in Science, reveals how NREM sleep – such as in a nap – fosters brain synchronisation and enhances information encoding, shedding new light on this sleep stage. The researchers replicated these effects through invasive stimulation, suggesting promising possibilities for future neuromodulation therapies in humans. The implications of this discovery potentially pave the way for innovative treatments for sleep disorders and even methods to enhance cognitive and behavioural performance.

The investigation involved an examination of the neural activity in multiple brain areas in macaques while the animals performed a visual discrimination task before and after a 30-minute period of NREM sleep. Using multielectrode arrays, the researchers recorded the activity of thousands of neurons across three brain areas: the primary and midlevel visual cortices and the dorsolateral prefrontal cortex, which are associated with visual processing and executive functions. To confirm that the macaques were in NREM sleep, researchers used polysomnography to monitor their brain and muscle activity alongside video analysis to ensure their eyes were closed and their bodies relaxed.

The findings demonstrated that sleep improved the animals’ performance in the visual task with enhanced accuracy in distinguishing rotated images. Meanwhile, the macaques that experienced quiet wakefulness without falling asleep did not show the same performance boost.

“During sleep, we observed an increase in low-frequency delta wave activity and synchronised firing among neurons across different cortical regions,” said first author Dr Natasha Kharas. “After sleep, however, neuronal activity became more desynchronised compared to before sleep, allowing neurons to fire more independently. This shift led to improved accuracy in information processing and performance in the visual tasks.”

The researchers also simulated the neural effects of sleep through low-frequency electrical stimulation of the visual cortex. They applied a 4-Hz stimulation to mimic the delta frequency observed during NREM sleep while the animals were awake. This artificial stimulation reproduced the desynchronization effect seen after sleep and similarly enhanced the animals’ task performance, suggesting that specific patterns of electrical stimulation could potentially be used to emulate the cognitive benefits of sleep.

“This finding is significant because it suggests that some of the restorative and performance-enhancing effects of sleep might be achieved without the need for actual sleep,” said Dragoi, study co-author, professor of electrical and computer engineering at Rice and professor of neuroscience at Weill Cornell. “The ability to reproduce sleeplike neural desynchronisation in an awake state opens new possibilities for enhancing cognitive and perceptual performance in situations where sleep is not feasible – such as for individuals with sleep disorders or in extenuating circumstances such as space exploration.”

The researchers further investigated their findings by building a large neural network model. They found that during sleep, both excitatory and inhibitory connections in the brain become weaker, but they do so asymmetrically, making inhibitory connections weaker than excitatory connections, which causes an increase in excitation.

“We have uncovered a surprising solution that the brain employs after sleep whereby neural populations participating in the task reduce their level of synchrony after sleep despite receiving synchronizing inputs during sleep itself,” Dragoi said.

The idea that NREM sleep effectively “boosts” the brain in this way, and that this resetting can be mimicked artificially, offers potential for developing therapeutic brain stimulation techniques to improve cognitive function and memory.

“Our study not only deepens our mechanistic understanding of sleep’s role in cognitive function but also breaks new ground by showing that specific patterns of brain stimulation could substitute for some benefits of sleep, pointing toward a future where we might boost brain function independently of sleep itself,” Dragoi said.

Source: Rice University