Why sleep affects Alzheimer’s disease? Research on the role of sleep in hydra, a fresh water polyp that is sleep deprived during the day
Despite many studies, there is no consensus on why sleep is important for survival. But the consequences of not getting enough of this fundamental physical process bear out the importance of continuing to seek answers.
The amount of sleep is important, but it isn’t the only one. If the amount of sleep is adequate, it could improve memory consolidation. And researchers have found a way to artificially increase deep, or slow-wave, sleep in humans — by delivering acoustic stimulation in the form of soft pulses of ‘pink noise’ to a sleeping person through a headset. Unlike the familiar white noise, which contains equal parts of the sound spectrum, pink noise contains more low- than high-frequency sounds.
In 2020, researchers found that hydra, a freshwater polyp with no brain, also enter a languid state at night11. These creatures show a need for sleep homeostasis as well, resting longer the day after being sleep deprived.
Nedergaard’s theory about sleep and the link between sleep and Alzheimer’s disease was disputed as an incomplete explanation. Nick Franks, a biophysicist at Imperial College London, is the most prominent challenge to her ideas. In May 2024, Franks and his colleagues used a fluorescent tracer to show that brain clearance is actually reduced during sleep10.
Sleep has several mechanisms that help the brain to reset after the stimulus and onslaught of information of each day. The brain’s part of the hippocampus goes silent during sleep, preparing it for use the next day. Sleep can restore the balance of junctions in the brain of mice, which shrink during the day and grow in the night, according to a study.
This finding sent Nedergaard and her colleagues searching for the drivers of that fluid clearance. One way the heart is, Nedergaard believes it is more likely to account for movement of fluid than its clearance. In February9, she and her colleagues reported that norepinephrine, which induces vasoconstriction, is the main promoter of clearance through “spontaneous, rhythmic constriction and dilation of arteries”. It is possible to see regular levels of norepinephrine in the brain when you sleep.
Sleep can help memories to take root and clear the brain of unnecessary information. Neuroscientist Maiken Nedergaard at the University of Rochester in New York, has a theory of how that cleaning occurs.
In a small study7, half of the participants received pink-noise acoustic stimulation and the other half wore headsets playing a different sound pattern, as a control. Researchers monitored brain activity with an electroencephalogram and found that pink-noise recipients had increased slow-wave activity. They had increased memory retention the next day.
Why sleep is essential — researchers are trying to work out why] (An Experimental Study in Brazil by e-matrix et al. D41586-025-00964-w)
The main purpose of sleep was to maintain brain health. There is so much brain development at those stages, that babies and teenagers sleep for long periods of time.
In rats, most genes seem to be upregulated while the animals are awake and downregulated during sleep. Genes that are upregulated during periods of sleep deprivation are responsible for functions such as energy metabolism, hormone reception and protein synthesis5. Fruit flies that were sleep deprived had over expression of genes that affect metabolism and dopamine6 levels, according to a study done in Brazil.
The same happened in mice. When the animals were sleep deprived, then allowed to sleep for small periods, during that time, they stopped expressing genes for fat uptake. The proliferation of cells in the gut that are better at absorption can be stimulated by ROS through an organelles called mitochondria. The mice were restricted from sleeping on the first day, but after a couple of hours, it became apparent that fats weren’t going into circulation. Their guts were filled with fat despite their lack of nutrition.
Source: Sleep is essential — researchers are trying to work out why
How flies get their nutrients, but what does it take to get their bodies to recover? A study of homeostasis by a deep-learning network
“We looked at tissues all over the body,” Vaccaro says. We did not see anything when we looked at the brain. The one tissue that was the most damaged when flies died was the gut.
After he was able to determine the ten day timeline for sleep deprivation and death in flies, he began to look for markers of aging in these insects. She and her colleagues found that the concentrations of reactive oxygen species (ROS) in the guts of flies were at their highest when the animals started dying. ROS are beneficial because they regulate the body’s immune response and help cells defend against pathogens. But without sleep these molecules accumulate to toxic levels4.
Likewise, when the brain is further from its critical point, a person will feel more tired and need to fall asleep to reset. The closer the brain is to its critical point, the more likely someone is to stay awake.
Hengen compares homeostasis to the familiar workings of a home heating system. The environment changes to the desired level of warmth when a room’s temperature falls below the set point.
“This was like a light bulb for me a long time ago,” Hengen says. In terms of machine learning, “if you have a deep-learning network, and you continue to let it learn, it’ll exhibit catastrophic forgetting — the wheels come off and the thing stops. It just fails.”
Source: Sleep is essential — researchers are trying to work out why
The effect of daytime light exposure and physical activity on postpartum insomnia in first-time parents of children – A study by the University of Washington University
What’s the most important function of the brain? It might be tempting to say a specific task, such as communicating, finding food or avoiding predators. But none of these roles is possible if the brain’s cellular machinery isn’t functioning reliably. The main purpose of sleep is reliability, says a neuroscientist at Washington University.
The moment sleep-deprived animals start dying was the same every time. They started dying after losing about 10% of their sleep each night. Those studies were in flies and mice — but the implications for other animals, including humans, was intriguing.
She expected it would take years to answer these questions. In a period of only six months, his assistant found a clue.
A study has found that exposure to too much light when we’re supposed to be asleep is linked to an increased risk of mental illness. Researchers in Australia, the United States and the United Kingdom analysed data from almost 87,000 people registered with the UK Biobank study who had completed 7 days of round-the-clock measurements of their light exposure and physical activity, including sleep. They were also asked about their mental-health.
Babies are bad enough for parental sleep without the extra burden of pre-existing insomnia. In an effort to help first-time parents who are struggling with these dual sleep challenges, researchers in Australia and Israel trialled two interventions aimed at reducing postpartum insomnia in 127 individuals who were due to give birth to their first child.
The mechanism underpinning these effects is not clear. It is possible for excessive napping to indicate inadequate night-time sleep. There are mechanisms in which daytime naps can have an influence on cardiovascular disease risk.
A study has confirmed that early morning lectures aren’t attended, and that the few who do attend are too tired to learn.
The study found that alcohol increased the amount of time spent in deep, slow-wave sleep in the first third of the night, but decreased it thereafter. The first night of drinking saw the most pronounced changes, including a reduction in REM sleep. That result suggested a growing tolerance to the effects of alcohol on sleep over multiple days.
One hour before lights out, 30 healthy adults aged 22 to 57 were given a drink that contained either a mixer or a mixer plus alcohol, which was designed to bring them to a blood alcohol level of 0.08 milligrams per litre — around four drinks for the average man. The participants were wired up to record their brain activity during the night. After three nights, the two groups were swapped over to the opposite drink type for a further three nights.
There is a possibility that the age-old practice of rocking someone to sleep can be used to improve sleep quality in those with diseases that impair sleep quality.
The team found that those that had been vibrated to sleep showed healthier courtship behaviour than did flies that had not, and therefore had not slept much.