REM sleep tunes eating behavior
August 6, 2020
Science Daily/University of Bern
Despite our broad understanding of the different brain regions activated during rapid-eye-movement sleep, little is known about what this activity serves for. Researchers at the University of Bern and the Inselspital have now discovered that the activation of neurons in the hypothalamus during REM sleep regulates eating behaviour: suppressing this activity in mice decreases appetite.
While we are asleep, we transition between different phases of sleep each of which may contribute differently to us feeling rested. During (rapid eye movement) REM sleep, a peculiar sleep stage also called paradoxical sleep during which most dreaming occurs, specific brain circuits show very high electrical activity, yet the function of this sleep-specific activity remains unclear.
Among the brain regions that show strong activation during REM sleep are areas that regulate memory functions or emotion, for instance. The lateral hypothalamus, a tiny, evolutionarily well conserved brain structure in all mammals also shows high activity during REM sleep. In the awake animals, neurons from this brain region orchestrate appetite and the consumption of food and they are involved in the regulation of motivated behaviours and addiction.
In a new study, researchers headed by Prof. Dr. Antoine Adamantidis at the University of Bern set out to investigate the function of the activity of hypothalamic neurons in mice during REM sleep. They aimed at better understanding how neural activation during REM sleep influences our day-to-day behaviour. They discovered that suppressing the activity of these neurons decreases the amount of food the mice consume. "This suggests that REM sleep is necessary to stabilize food intake," says Adamantidis. The results of this study have been published in the journal Proceedings of the National Academy of Sciences (PNAS).
Long-lasting effect on neuronal activity and feeding behavior
The researcher discovered that specific activity patterns of neurons in the lateral hypothalamus that usually signal eating in the awake mouse are also present when the animals were in the stage of REM sleep. To assess the importance of these activity patterns during REM sleep the research group used a technique called optogenetics, with which they used light pulses to precisely shut down the activity of hypothalamic neurons during REM sleep. As a result, the researchers found that the activity patterns for eating were modified and that the animals consumed less food.
"We were surprised how strongly and persistently our intervention affected the neural activity in the lateral hypothalamus and the behaviour of the mice," says Lukas Oesch, the first author of the study. He adds: "The modification in the activity patterns was still measurable after four days of regular sleep." These findings suggest that electrical activity in hypothalamic circuits during REM sleep are highly plastic and essential to maintain a stable feeding behaviour in mammals.
It is a question of quality
These findings point out that sleep quantity alone is not solely required for our well-being, but that sleep quality plays a major role in particular to maintain appropriate eating behaviour. "This is of particular relevance in our society where not only sleep quantity decreases but where sleep quality is dramatically affected by shift work, late night screen exposure or social jet-lag in adolescents," explains Adamantidis.
The discovered link between the activity of the neurons during REM sleep and eating behaviour may help developing new therapeutical approaches to treat eating disorders. It might also be relevant for motivation and addiction. "However, this relationship might depend on the precise circuitry, the sleep stage and other factors yet to be uncovered," adds Adamantidis.
https://www.sciencedaily.com/releases/2020/08/200806111820.htm
The dreaming brain tunes out the outside world
May 15, 2020
Science Daily/CNRS
Scientists from the CNRS and the ENS-PSL in France and Monash University in Australia have shown that the brain suppresses information from the outside world, such as the sound of a conversation, during the sleep phase linked to dreaming. This ability could be one of the protective mechanisms of dreams. The study, carried out in collaboration with the Centre du Sommeil et de la Vigilance, Hôtel-Dieu, AP-HP -- Université de Paris, is published in Current Biology on 14 May 2020.
While we dream, we invent worlds that bear no relation to the quietness of our bedroom. In fact, it is rather unusual for elements of our immediate environment to be incorporated into our dreams. To better understand how the brain protects itself from outside influences, researchers invited 18 participants to a morning nap in the lab. Morning sleep is rich in dreams. Dreams mostly occur during what is known as REM sleep, since the brain is somehow in a waking state during this phase of sleep, showing brain activity similar to that when a person is awake. The body, on the other hand, is paralysed, although not entirely. During certain phases of REM sleep, the eyes continue to move. Research has shown that such movements are related to dreaming.
To study how the dreaming brain interacts with external sounds, the scientists got volunteer sleepers to listen to stories in French mixed with meaningless language. By combining the electroencephalogram with a machine learning technique, they confirmed that, even when the brain is asleep, it continues to record everything that goes on around it. They also showed that, during light sleep, the brain prioritises meaningful speech, just as it does when in the waking state. However, such speech is actively filtered out during eye movement phases in REM sleep. In other words, our sleeping brain can select information from the outside world and flexibly amplify or suppress it, depending on whether or not it is immersed in a dream!
The team believe that this mechanism enables the brain to protect the dreaming phase, which is necessary for emotional balance and consolidation of the day's learning. Although dreams are predominant during periods of eye movement, they can also occur during other phases of sleep. Are they then accompanied by a similar suppression of sensations from the outside world?
https://www.sciencedaily.com/releases/2020/05/200515131915.htm
REM sleep silences the siren of the brain
Restless REM sleep a risk for many mental disorders?
July 11, 2019
Science Daily/Netherlands Institute for Neuroscience - KNAW
Upset by something unpleasant? We have all been there. Fortunately, it also passes. A new day, a new beginning. At least: if you have restful REM sleep. Researchers at the Netherlands Institute for Neuroscience discovered why you will be better able to bear tomorrow what you are distressed about today. And why that can go wrong.
Siren of the brain
Something frightening or unpleasant does not go unnoticed. In our brain, the so-called limbic circuit of cells and connections immediately becomes active. First and foremost, such experiences activate the amygdala. This nucleus of brain cells located deep in the brain can be regarded as the siren of the brain: attention! In order for the brain to function properly, the siren must also be switched off again. For this, a restful REM sleep, the part of the sleep with the most vivid dreams, turns out to be essential.
Good sleepers
The researchers placed their participants in a MRI scanner in the evening and presented a specific odor while they made them feel upset. The brain scans showed how the amygdala became active. The participants then spent the night in the sleep lab, while the activity of their sleeping brain was measured with EEG, and the specific odor was presented again on occasion. The next morning, the researchers tried to upset their volunteers again, in exactly the same way as the night before. But now they did not succeed so well in doing this. Brain circuits had adapted overnight; the siren of the brain no longer went off. The amygdala responded much less, especially in those who had had a lot of restful REM sleep and where meanwhile exposed to the specific odor.
Restless sleepers
However, among the participants were also people with restless REM sleep. Things went surprisingly different for them. Brain circuits had not adapted well overnight: the siren of the brain continued to sound the next morning. And while the nocturnal exposure to the odor helped people with restful REM sleep adapt, the same exposure only made things worse for people with restless REM sleep.
Neuronal connections weaken and strengthen
During sleep, 'memory traces' of experiences from the past day are spontaneously played back, like a movie. Among all remnants of the day, a specific memory trace can be activated by presenting the same odor as the one that was present during the experience while awake. Meanwhile, memory traces are adjusted during sleep: some connections between brain cells are strengthened, others are weakened. Restless REM sleep disturbs these nocturnal adjustments, which are essential for recovery and adaptation to distress.
Transdiagnostic importance
The findings were published on 11 July in the leading journal Current Biology. The finding can be of great importance for about two-thirds of all people with a mental disorder, as both restless REM sleep and a hyperactive amygdala are the hallmarks of post-traumatic stress disorder (PTSD), anxiety disorders, depression and insomnia. People with PTSD carry their traumatic experience to the next day: people with an anxiety disorder take their greatest fear with them, people with depression their despair, and people with chronic insomnia their tension. Authors Rick Wassing, Frans Schalkwijk and Eus van Someren predict that treatment of restless REM sleep could transdiagnostically help to process emotional memories overnight and give them a better place in the brain.
https://www.sciencedaily.com/releases/2019/07/190711141258.htm
Neural sleep patterns emerged at least 450 million years ago
July 10, 2019
Science Daily/Stanford Medicine
Researchers at the Stanford University School of Medicine have found that neural signatures in sleeping zebrafish are analogous to those of humans, suggesting that the brain activity evolved at least 450 million years ago, before any creatures crawled out of the ocean.
Scientists have known for more than 100 years that fish enter a sleeplike state, but until now they didn't know if their sleep resembled that of land animals.
The researchers found that when zebrafish sleep, they can display two states that are similar to those found in mammals, reptiles and birds: slow-wave sleep and paradoxical, or rapid eye movement, sleep. The discovery marks the first time these brain patterns have been recorded in fish.
"This moves the evolution of neural signatures of sleep back quite a few years," said postdoctoral scholar Louis Leung, PhD.
A paper describing the research will be published July 10 in Nature. Philippe Mourrain, PhD, associate professor of psychiatry and behavioral sciences, is the senior author. Leung is the lead author.
To study the zebrafish, common aquarium dwellers also known as danios, the researchers built a benchtop fluorescent light-sheet microscope capable of full-fish-body imaging with single-cell resolution. They recorded brain activity while the fish slept in an agar solution that immobilized them. They also observed the heart rate, eye movement and muscle tone of the sleeping fish using a fluorescence-based polysomnography that they developed.
They named the sleep states they observed "slow-bursting sleep," which is analogous to slow-wave sleep, and "propagating-wave sleep," analogous to REM sleep. Though the fish don't move their eyes during REM sleep, the brain and muscle signatures are similar. (Fish also don't close their eyes when they sleep, as they have no eyelids.)
Sleeping like the fish
The researchers found another similarity between fish and human sleep. By genetically disrupting the function of melanin-concentrating hormone, a peptide that governs the sleep-wake cycle, and observing neural expressions as the fish slept, the researchers determined that the hormone's signaling regulates the fish's propagating wave sleep the way it regulates REM sleep in mammals.
Other aspects of their sleep state are similar to those of land vertebrates, Mourrain said: The fish remain still, their muscles relax, their cardio-respiratory rhythms slow down and they fail to react when they're approached.
"They lose muscle tone, their heartbeat drops, they don't respond to stimuli -- the only real difference is a lack of rapid eye movement during REM sleep," Mourrain said, though he added, "The rapid movement of the eyes is not a good criterion of this state, and we prefer to call it paradoxical sleep, as the brain looks awake while one is asleep."
While scientists can't say for certain that all animals sleep, it appears to be a universal need among vertebrates and invertebrates. Animals will die if they are deprived of sleep long enough, and people who fail to receive adequate sleep suffer from mental problems such as memory lapses and impaired judgment, along with a higher risk of disorders such as obesity and high blood pressure.
The exact benefits of sleep are still a mystery, however. "It's an essential function," Mourrain said, "but we don't know precisely what it does."
He added that sleep disorders are linked to most neurological disorders such as autism spectrum disorders, Fragile X syndrome, and Alzheimer's and Parkinson's disease. "Sleep disturbances are an aggravating factor of these disorders," Mourrain said. It is critical to develop this animal model to study sleep functions at the cellular level, including neuronal connectivity and DNA repair, and in turn understand the pathophysiological consequences of sleep disruptions, he added.
The discovery means sleep research can be conducted on zebrafish, which are easy to study, in part because they're transparent. They breed quickly, are inexpensive to care for and are just over an inch long. Drug testing requires only the addition of chemicals to their water.
"Because the fish neural signatures are in essence the same as ours, we can use information about them to generate new leads for drug trials," Leung said. He added that mice, often a stand-in for human research, are nocturnal and a less relevant model for our sleep.
"As zebrafish are diurnal like humans, it's perhaps more biologically accurate to compare fish sleep with humans' for some aspects," Leung said.
https://www.sciencedaily.com/releases/2019/07/190710132015.htm
'Goldilocks' neurons promote REM sleep
June 19, 2019
Science Daily/University of Bern
It has been a mystery why REM sleep, or dream sleep, increases when the room temperature is 'just right'. Neuroscientists show that melanin-concentrating hormone neurons within the hypothalamus increase REM sleep when the need for body temperature defense is minimized, such as when sleeping in a warm and comfortable room temperature. These data have important implications for the function of REM sleep.
Every night while sleeping, we cycle between two very different states of sleep. Upon falling asleep, we enter non-rapid eye movement (non-REM) sleep where our breathing is slow and regular and movement of our limbs or eyes are minimal. Approximately 90 minutes later, how-ever, we enter rapid eye movement (REM) sleep. This is a paradoxical state where our breathing becomes fast and irregular, our limbs twitch, and our eyes move rapidly. In REM sleep, our brain is highly active, but we also become paralyzed and we lose the ability to thermoregulate or maintain our constant body temperature. "This loss of thermoregulation in REM sleep is one of the most peculiar aspects of sleep, particularly since we have finely-tuned mechanisms that control our body temperature while awake or in non-REM sleep," says Markus Schmidt of the Department for BioMedical Research (DBMR) of the University of Bern, and the Department of Neurology, Inselspital, Bern University Hospital. On the one hand, the findings confirm a hypothesis proposed earlier by Schmidt, senior author of the study, and on the other hand represent a breakthrough for sleep medicine. The paper was published in Current Biology and highlighted by the editors with a comment.
A control mechanism saving energy
The need to maintain a constant body temperature is our most expensive biological function. Panting, piloerection, sweating, or shivering are all energy consuming body reactions. In his hypothesis, Markus Schmidt suggested that REM sleep is a behavioral strategy that shifts energy resources away from costly thermoregulatory defense toward, instead, the brain to enhance many brain functions. According to this energy allocation hypothesis of sleep, mammals have evolved mechanisms to increase REM sleep when the need for defending our body temperature is minimized or, rather, to sacrifice REM sleep when we are cold. "My hypothesis predicts that we should have neural mechanisms to dynamically modulate REM sleep expression as a function of our room temperature," says Schmidt. Neuroscientists at the DBMR at the University of Bern and the Department of Neurology at Inselspital, Bern University Hospital, now confirmed his hypothesis and found neurons in the hypothalamus that specifically increase REM sleep when the room temperature is "just right."
REM sleep promoting neurons
The researchers discovered that a small population of neurons within the hypothalamus, called melanin-concentrating hormone (MCH) neurons, play a critical role in how we modulate REM sleep expression as a function of ambient (or room) temperature. The researchers showed that mice will dynamically increase REM sleep when the room temperature is warmed to the high end of their comfort zone, similar to what has been shown for human sleep. However, genetically engineered mice lacking the receptor for MCH are no longer able to increase REM sleep during warming, as if they are blind to the warming temperature. The authors used optogenetics technics to specifically turn on or off MCH neurons using a laser light time locked to the temperature warming periods. Their work confirms the necessity of the MCH system to increase REM sleep when the need for body temperature control is minimized.
Breakthrough for sleep medicine
This is the first time that an area of the brain has been found to control REM sleep as a function of room temperature. "Our discovery of these neurons has major implications for the control of REM sleep," says Schmidt. "It shows that the amount and timing of REM sleep are finely tuned with our immediate environment when we do not need to thermoregulate. It also con-firms how dream sleep and the loss of thermoregulation are tightly integrated."
REM sleep is known to play an important role in many brain functions such as memory consolidation. REM sleep comprises approximately one quarter of our total sleep time. "These new data suggest that the function of REM sleep is to activate important brain functions specifically at times when we do not need to expend energy on thermoregulation, thus optimizing use of energy resources," says Schmidt.
https://www.sciencedaily.com/releases/2019/06/190619111248.htm
An epidemic of dream deprivation: Unrecognized health hazard of sleep loss
September 29, 2017
Science Daily/University of Arizona Health Sciences
A sleep and dream specialist has completed a comprehensive review of data about the causes, extent and consequences of dream loss includes recommendations for restoring healthy dreaming.
A silent epidemic of dream loss is at the root of many of the health concerns attributed to sleep loss, according to Rubin Naiman, PhD, a sleep and dream specialist at the University of Arizona Center for Integrative Medicine, who recently published a comprehensive review of data.
His review, "Dreamless: the silent epidemic of REM sleep loss" in the "Unlocking the Unconscious: Exploring the Undiscovered Self" issue of the Annals of the New York Academy of Sciences, details the various factors that cause rapid eye movement (REM) sleep and dream loss. Typical sleep follows a pattern in which deeper, non-REM sleep is prioritized by the body. Only later in the night and into the early morning do people experience dreaming, during REM sleep.
"We are at least as dream-deprived as we are sleep-deprived," noted Dr. Naiman, UA clinical assistant professor of medicine. He sees REM/dream loss as an unrecognized public health hazard that silently wreaks havoc by contributing to illness, depression and an erosion of consciousness. "Many of our health concerns attributed to sleep loss actually result from REM sleep deprivation."
The review examines data about the causes and extent of REM/dream loss associated with medications, substance use disorders, sleep disorders and behavioral and lifestyle factors. Dr. Naiman further reviews the consequences of REM/dream loss and concludes with recommendations for restoring healthy REM sleep and dreaming.
https://www.sciencedaily.com/releases/2017/09/170929093254.htm
Fat Intake Negatively Influences the Sleep Pattern in Healthy Adults
June 12, 2008
Science Daily/American Academy of Sleep Medicine
Total fat intake and dinner fat intake seem to influence negatively the sleep pattern in healthy adults, according to a research abstract that will be presented on June 10 at SLEEP 2008, the 22nd Annual Meeting of the Associated Professional Sleep Societies (APSS).
"We showed that an increased fat intake was associated with a lower percentage of REM sleep, a higher arousal index and apnea-hypopnea index, and a lower sleep efficiency," said Crispim. "These results showed that total fat intake and dinner fat intake seem to influence negatively the sleep pattern. However, researches in the nutrition and sleep area should be carried out to better understand these associations."
"Previous studies have demonstrated that circadian distribution of food intake is capable of modifying endocrine and metabolic patterns during sleep. However, studies of the influence of food intake distribution on sleep pattern are scarce. This study, which analyzed the influence of energy intake on the sleep patterns in healthy subjects, concluded that total energy intake and late-night snack energy intake may increase sleep fragmentation in healthy subjects, which might increase the effects of sleep restriction on nutritional and metabolic balance. New studies on this area are needed to better understand theses associations," said Zalcman.
http://www.sciencedaily.com/releases/2008/06/080610072056.htm
Fear, safety and the role of sleep in human PTSD: Fragmented REM sleep may hinder effective treatment
August 27, 2014
Science Daily/University of California, San Diego Health Sciences
The effectiveness of post-traumatic stress disorder (PTSD) treatment may hinge significantly upon sleep quality, report researchers. PTSD is an often difficult-to-treat mental health condition triggered by a terrifying event. It is characterized by severe anxiety, flashbacks, nightmares and uncontrollable thoughts, often fearful. Research has shown that fear conditioning, considered an animal model of PTSD, results in disruption of animals' rapid eye movement (REM) sleep -- periods of deeper, dream-filled slumber.
"I think these findings help us understand why sleep disturbances and nightmares are such important symptoms in PTSD," said Sean P.A. Drummond, PhD, professor of psychiatry and director of the Behavioral Sleep Medicine Program at the VA San Diego Healthcare System. "Our study suggests the physiological mechanism whereby sleep difficulties can help maintain PTSD. It also strongly implies a mechanism by which poor sleep may impair the ability of an individual to fully benefit from exposure-based PTSD treatments, which are the gold standard of interventions.
"The implication is that we should try treating sleep before treating the daytime symptoms of PTSD and see if those who are sleeping better when they start exposure therapy derive more benefit."
PTSD is an often difficult-to-treat mental health condition triggered by a terrifying event. It is frequently associated with persons who have served in war zones and is characterized by severe anxiety, flashbacks, nightmares and uncontrollable thoughts, often fearful.
Research has shown that fear conditioning, considered an animal model of PTSD, results in disruption of animals' rapid eye movement (REM) sleep -- periods of deeper, dream-filled slumber. Fear conditioning is a form of learning in which the animal model is trained to associate an aversive stimulus, such as an electrical shock, with a neutral stimulus, such as a tone or beep.
"In PTSD, humans learn to associate threat with a stimulus that used to be neutral or even pleasant. Often, this fear generalizes so that they have a hard time learning that other stimuli are safe. For example, a U.S. Marine in Iraq might suffer trauma when her personnel carrier is blown up by road side bomb hidden in trash alongside the road. When she comes home, she should learn that trash on the side of I-5 does not pose a threat -- it's a safe stimulus -- but that may be difficult for her."
The researchers found that increased safety signaling was associated with increased REM sleep consolidation at night and that the quality of overnight REM sleep was related to how well volunteers managed fear conditioning.
Drummond said stimuli representing safety increased human REM sleep and that "helps humans distinguish threatening stimuli from safe stimuli the next day. So while animal studies focused on learning and unlearning a threat, our study showed REM sleep in humans is more related to learning and remembering safety."
"A very large percentage of missions in both Iraq and Afghanistan were at night," said Drummond, who is also associate director of the Mood Disorders Psychotherapy Program at VA San Diego Healthcare System. "So soldiers learned the night was a time of danger. When they come home, they have a hard time learning night here is a time to relax and go to sleep."
http://www.sciencedaily.com/releases/2014/08/140827090138.htm