Sleep Study

  • Sleep Health, Sleep Study, Uncategorized

    8 Health Problems Linked to Not Getting Enough Sleep

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    Original Post | Why Not Getting Enough Sleep Is Bad for Your Health

    A good night’s sleep helps you feel refreshed and perform better the following day. But there’s growing evidence that sleep is critical for maintaining good long-term health, too.

    The body can usually cope with occasionally staying up late, but if you’re frequently or chronically depriving yourself of sleep, there will be a price to pay, says Sigrid C. Veasey, MD, a researcher and professor of medicine at Penn Medicine in Philadelphia.Here are some of the long-term health problems linked to not clocking enough hours of shut-eye.

    Why Sleep Is So Good for Your Immune System

    Learn how sleep boosts your immune system and why it’s essential for overall health.

    1. Poor Brain Health

    Studies have linked sleep problems to poor thinking and memory skills later in life, which could put people at higher risk for dementia, says Clémence Cavaillès, PhD, a researcher at the University of California in San Francisco. 

    Bad sleep may also result in premature aging of the brain, says Dr. Cavaillès. She is the author of a recent study that found that people who have poor sleep quality have more signs of poor brain health as they get older compared with people who have fewer sleep issues.

    The study, which followed 600 middle-aged participants over 15 years, found that people with the greatest number of sleep complications had an average brain age that, over this time period, became 2.6 years more advanced than people with the fewest sleep issues. 

    Bad sleep quality, difficulty falling asleep, difficulty staying asleep, and early morning awakening were linked to greater brain age, especially if the issue persisted over five years. 

    A prematurely aging brain has significant implications for numerous aspects for cognitive health, daily functioning, and overall well-being, says Cavaillès.

    “Specifically, advanced brain aging has been associated with worse cognitive functions and Alzheimer disease–related atrophy patterns,” she says.

    Depression from Lack of Sleep

    2. Depression and Anxiety

    Research shows that people who have chronic insomnia have a higher rate of depression and anxiety compared with people who haven’t been diagnosed with insomnia, says Meena Khan, MD, a neurologist and sleep medicine specialist at The Ohio State University Wexner Medical Center in Columbus. It’s estimated that about 40 percent of people with insomnia have clinical depression.

    The relationship between mood and sleep is complex and bidirectional, which means that depression or anxiety can worsen sleep, and lack of sleep can also negatively impact mood. Insomnia is considered an independent risk factor for developing a mental health disorder, including depression, in people of all ages.

    Sometimes separate treatments are needed to help with the sleep problems and the anxiety or depression, but in some cases improving sleep can help mood, too, says Dr. Khan.

    3. Type 2 Diabetes

    Poor quality sleep or short sleep duration has been linked to poorer blood sugar control in people with and without diabetes, says Khan. It can increase risk of developing diabetes as well, she says.

    In a group of middle-aged Caucasians, researchers found a strong association between poor sleep quality and metabolic syndrome, insulin levels, fasting blood sugar levels, and insulin resistance, which is often a precursor to type 2 diabetes.

    4. Weight Gain and Obesity

    There is a strong link between having sleep issues and being overweight or having obesity. That’s because not getting enough sleep on a regular basis (sleep deprivation) can create an imbalance in the hormones that regulate your appetite, ghrelin and leptin.

    Leptin helps you feel full, and ghrelin makes you feel hungry. Because leptin levels typically rise during sleep, experts think if you aren’t getting enough, your leptin levels decrease, making you feel hungrier, and that may lead to eating more than you need. On top of that, sleep disruptions of any kind can cause an increase in ghrelin, which also increases your appetite.

    Research suggests that insufficient sleep makes people burn about 100 more calories a day. Although that sounds like a good thing, the extra wake time also increases how much people eat or drink by more than 250 calories, which over time can make people gain weight.

    5. Hypertension, Heart Disease, and Stroke

    The American Heart Association (AHA) includes sleep in its “Life’s Essential 8,” a checklist of modifiable factors that can improve heart health.

    Even small changes in sleep have been linked to heart issues. There are 24 percent more heart attacks for the first three to four days after the clocks change in March, and a 21 percent reduction in heart attack risks in November when clocks “fall back” and people gain an hour of sleep.

    Regularly sleeping five hours or less is associated with a 2 to 3 times greater risk of coronary artery buildup (decreasing the blood flow to your heart), meaning that sleep deprivation may increase the likelihood of coronary artery disease.

    People with obstructive sleep apnea (OSA) have higher risk of hypertension, heart attack, and stroke, says Khan.

    6. Kidney Problems

    The link between sleep and kidney health hasn’t been as firmly established as the link between sleep and other chronic conditions, says Khan.

    People with chronic kidney disease often have sleep disorders such as restless leg syndrome and insomnia related to their condition.

    [10] But there’s evidence that poor sleep quality is associated with developing chronic kidney disease, which researchers believe could be related to the disruptions in circadian rhythms.

    7. Impaired Immune Function

    Not getting enough or good enough quality sleep can shortchange your immune system, says Khan.

    “There is evidence that getting plenty of sleep can benefit your immune system and that impaired sleep is linked with being more susceptible to infections,” she says.

    Research has linked poor sleep to an increased susceptibility to certain types of illness. People who chronically get less than seven hours of sleep a night are 3 times as likely to develop the common cold compared with those who routinely get eight hours or more of sleep.

    Additionally, studies on flu vaccines and hepatitis A and B vaccines suggest that not sleeping hurts your body’s ability to make disease-fighting antibodies. When study participants were deprived of sleep for about four hours a night in the days before and one to two days following vaccination, they developed a significantly lower level of antibodies compared to those who were not sleep-deprived.

    8. A Less Healthy Gut

    The gut microbiome is all the microorganisms such as bacteria and fungi that are found in the gastrointestinal tract, and experts believe that the more diverse the microbiome, the better it is for overall health.

    There are some studies that suggest that altered sleep — for example, what night shift workers would experience — may impact your gut health, Khan says.

    A study using Mendelian randomization, a method that uses genetic variation to study causal effects of different health variables, found that sleep issues may alter the abundance of gut microbiota.

    Investigators also found several types of gut bacteria may be involved in many different aspects of sleep regulation, which suggests the relationship between sleep and the gut goes in both directions. 

    The Takeaway

     

      • Poor sleep quality may lead to cognitive problems and a higher risk of dementia, with studies showing a correlation between sleep issues and accelerated brain aging.

      • Chronic sleep deprivation significantly increases the risk of depression and anxiety, with about 40 percent of those with insomnia experiencing clinical depression.

      • Sleep problems are associated with increased risk of type 2 diabetes and metabolic syndrome due to impaired blood sugar control.

      • Regularly getting less than five hours of sleep is linked to a higher risk of hypertension, heart disease, and stroke, potentially increasing coronary artery disease risk.

  • Sleep, Sleep Apnea, Sleep Study

    Why the First Half of Your Sleep is Crucial for Brain Reset

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    Original Article | Sleep Review Magazine

    Recent findings reveal that the initial hours of sleep play a crucial role in weakening neuron connections, paving the way for new learning the following day.

    Summary: A study by University College London, published in Nature, shows that during the first half of sleep, the brain reduces connections made between neurons while awake, supporting the Synaptic Homeostasis Hypothesis. This “reset” prepares the brain for new learning. Using zebrafish with optically translucent genes for easy imaging of synapses, researchers found that sleep helps manage the strength of neuron connections based on prior wakefulness. The study raises questions about the second half of sleep, suggesting it might serve other brain functions like waste clearance or cell repair.

    Key Takeaways: 

    • The first half of sleep is crucial for weakening the connections between neurons that are formed during wakefulness, helping to reset the brain for new learning the next day.
    • The study utilized optically translucent zebrafish, allowing researchers to visually track how synapses in the brain were altered during different sleep-wake cycles.
    • While the first half of sleep focuses on synaptic weakening, the function of the second half remains less understood, with theories suggesting it may involve brain waste clearance or cell repair.

    During sleep, the brain weakens the new connections between neurons that had been forged while awake—but only during the first half of a night’s sleep, according to a new study in fish by University College London scientists.

    The researchers say their findings, published in Nature, provide insight into the role of sleep but still leave an open question about what function the latter half of a night’s sleep serves. The researchers say the study supports the Synaptic Homeostasis Hypothesis, a key theory on the purpose of sleep which proposes that sleeping acts as a reset for the brain.

    “When we are awake, the connections between brain cells get stronger and more complex. If this activity were to continue unabated, it would be energetically unsustainable. Too many active connections between brain cells could prevent new connections from being made the following day,” says lead author professor Jason Rihel, PhD, in a release. “While the function of sleep remains mysterious, it may be serving as an ‘offline’ period when those connections can be weakened across the brain, in preparation for us to learn new things the following day.”

    Study Shows Sleep’s Impact on Brain

    For the study, the scientists used optically translucent zebrafish, with genes enabling synapses to be easily imaged. The research team monitored the fish over several sleep-wake cycles.

    The researchers found that brain cells gain more connections during waking hours and then lose them during sleep. They found that this was dependent on how much sleep pressure (need for sleep) the animal had built up before being allowed to rest; if the scientists deprived the fish from sleeping for a few extra hours, the connections continued to increase until the animal was able to sleep.

    “If the patterns we observed hold true in humans, our findings suggest that this remodeling of synapses might be less effective during a mid-day nap when sleep pressure is still low, rather than at night when we really need the sleep,” says Rihel in a release. 

    Neural Rearrangement Peaks in Early Sleep

    The researchers also found that these rearrangements of connections between neurons mostly happened in the first half of the animal’s nightly sleep. This mirrors the pattern of slow-wave activity, which is part of the sleep cycle that is strongest at the beginning of the night.

    “Our findings add weight to the theory that sleep serves to dampen connections within the brain, preparing for more learning and new connections again the next day,” says first author Anya Suppermpool, PhD, in a release. “But our study doesn’t tell us anything about what happens in the second half of the night. There are other theories around sleep being a time for clearance of waste in the brain, or repair for damaged cells—perhaps other functions kick in for the second half of the night.”

    Photo 97439374 © Siriporn Kaenseeya | Dreamstime.com

  • Sleep, Sleep Study

    Light at Night Tied to Diabetes Risk in Largest Study to Date

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    Original Article Medscape | Christina Szalinski

    Concerned about your patient’s type 2 diabetes risk? Along with the usual preventive strategies — like diet and exercise and, when appropriate, glucagon-like peptide 1 (GLP-1) agonists — there’s another simple, no-risk strategy that just might help: Turning off the light at night.

    A study in The Lancet found that people who were exposed to the most light between 12:30 AM and 6 AM were 1.5 times more likely to develop diabetes than those who remained in darkness during that timeframe.

    The study builds on growing evidence linking nighttime light exposure to type 2 diabetes risk. But unlike previous large studies that relied on satellite data of outdoor light levels (an indirect measure of light exposure), the recent study looked at personal light exposure — that is, light measured directly on individuals — as recorded by a wrist-worn sensor.

    “Those previous studies likely underestimated the effect,” said study author Andrew Phillips, PhD, professor of sleep health at Flinders University in Adelaide, Australia, “since they did not capture indoor light environments.”

    Using data from 85,000 participants from the UK Biobank, the recent study is the largest to date linking diabetes risk to personal light exposure at night.

    “This is really a phenomenal study,” said Courtney Peterson, PhD, a scientist at the University of Alabama at Birmingham’s Diabetes Research Center, who was not involved in the study. “This is the first large-scale study we have looking at people’s light exposure patterns and linking it to their long-term health.”

    What the Study Showed

    The participants wore the light sensors for a week, recording day and night light from all sources — whether from sunlight, lamps, streetlights, or digital screens. The researchers then tracked participants for 8 years.

    “About half of the people that we looked at had very dim levels of light at night, so less than one lux — that basically means less than candlelight,” said Phillips. “They were the people who were protected against type 2 diabetes.”

    Those exposed to more light at night — defined in the study as 12:30 AM-6 AM — had a higher risk for type 2 diabetes. The risk went up as a dose response, Phillips said: The brighter the light exposure, the higher the diabetes risk.

    Participants in the top 10% of light exposure — who were exposed to about 48 lux , or the equivalent of relatively dim overhead lighting — were 1.5 times more likely to develop diabetes than those in the dark. That’s about the risk increase you’d get from having a family history of type 2 diabetes, the researchers said.

    Even when they controlled for factors like socioeconomic status, smoking, diet, exercise, and shift work, “we still found there was this very strong relationship between light exposure and risk of type 2 diabetes,” said Phillips.

    How Light at Night May Increase Diabetes Risk

    The results are not entirely surprising, said endocrinologist Susanne Miedlich, MD, a professor at the University of Rochester Medical Center, Rochester, New York, who was not involved in the study.

    Light at night can disrupt the circadian rhythm, or your body’s internal 24-hour cycle. And scientists have long known that circadian rhythm is important for all kinds of biologic processes, including how the body manages blood sugar.

    One’s internal clock regulates food intake, sugar absorption, and the release of insulin. Dysregulation in the circadian rhythm is associated with insulin resistance, a precursor to type 2 diabetes.

    Phillips speculated that the sleep hormone melatonin also plays a role.

    “Melatonin does a lot of things, but one of the things that it does is it manages our glucose and our insulin responses,” Phillips said. “So if you’re chronically getting light exposure at night, that’s reducing a level of melatonin that, in the long term, could lead to poor metabolic outcomes.”

    Previous studies have explored melatonin supplementation to help manage diabetes. “However, while melatonin clearly regulates circadian rhythms, its utility as a drug to prevent diabetes has not really panned out thus far,” Miedlich said.

    Takeaways

    Interventional studies are needed to confirm whether strategies like powering down screens, turning off lights, or using blackout curtains could reduce diabetes risk.

    That said, “there’s no reason not to tell people to get healthy light exposure patterns and sleep, especially in the context of diabetes,” said Phillips.

    Other known strategies for reducing diabetes risk include intensive lifestyle programs, which reduce risk by up to 58%, and GLP-1 agonists.

    “Probably a GLP-1 agonist is going to be more effective,” Peterson said. “But this is still a fairly large effect without having to go through the expense of buying a GLP-1 or losing a lot of weight or making a big lifestyle change.”

  • Sleep Apnea, Sleep Health, Sleep Study

    Study reveals sleep effects how young you feel

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    By Eric Ralls Earth.com staff writer

    Have you ever noticed how a well-maintained classic car can turn heads and exude a timeless charm? Its age has become subjective. Just like a vintage automobile that has been meticulously cared for, feeling young is not merely a superficial notion — it is intrinsically connected to tangible health benefits.

    Subjective age, the internal gauge that measures how old we perceive ourselves to be, transcends the realm of simple self-perception.

    Much like how a classic car’s performance and longevity are tied to its upkeep, research has revealed that individuals who feel younger than their chronological age tend to enjoy longer lifespans, superior mental and physical well-being, and a host of positive psychological attributes.

    These findings have led experts to propose the integration of subjective age as a biophysical indicator of aging, serving as a vital component of comprehensive health assessments.

    Young and Youthful Woman

    Sleep-age connection

    Researchers at Stockholm University have discovered that sleep affects how old you feel. The study, published in the scientific journal Proceedings of the Royal Society B, reveals that feeling sleepy can make you feel ten years older.

    Leonie Balter, a researcher at the Department of Psychology, Stockholm University, explains, “Given that sleep is essential for brain function and overall well-being, we decided to test whether sleep holds any secrets to preserving a youthful sense of age.”

    Power of a good night’s sleep

    In the first study, 429 individuals aged 18 to 70 were asked how old they felt, how many days in the past month they had not gotten enough sleep, and how sleepy they were.

    The results showed that for each night with insufficient sleep in the past month, participants felt on average 0.23 years older.

    To further investigate the causal relationship between sleep and subjective age, the researchers conducted a second study involving 186 participants aged 18 to 46.

    Participants restricted their sleep for two nights, with only four hours in bed each night, and another time slept sufficiently for two nights, with nine hours in bed each night.

    The findings were striking. After sleep restriction, participants felt on average 4.4 years older compared to when having enjoyed sufficient sleep.

    Staying young at heart by safeguarding your sleep

    The effects of sleep on subjective age appeared to be related to how sleepy they felt. Feeling extremely alert was related to feeling 4 years younger than one’s actual age, while extreme sleepiness was related to feeling 6 years older than one’s actual age.

    “This means that going from feeling alert to sleepy added a striking 10 years to how old one felt,” says Leonie Balter.

    Previous studies have shown that feeling younger than one’s actual age is associated with longer, healthier lives. There is even support for subjective age to predict actual brain age, with those feeling younger having younger brains.

    The implications of this study are clear. “Safeguarding our sleep is crucial for maintaining a youthful feeling. This, in turn, may promote a more active lifestyle and encourage behaviours that promote health, as both feeling young and alert are important for our motivation to be active,” states Leonie Balter.

    Unlocking the secrets of age by sleeping

    In a world where we are constantly searching for the fountain of youth, it turns out that the secret to feeling young again might be as simple as getting a good night’s sleep.

    By prioritizing our sleep and ensuring that we get enough rest each night, we can not only feel more alert and energized but also maintain a youthful sense of age.

    So, the next time you find yourself longing for the vitality of your younger years, remember that the key to unlocking that feeling might just be a few extra hours of shut-eye.

    More about subjective age

    As discussed above, subjective age refers to how old an individual feels, regardless of their chronological age. It is a personal perception that can be influenced by various factors, such as physical health, mental well-being, and life experiences.

    People often report feeling younger or older than their actual age, and this subjective age can have significant implications for their overall health and quality of life.

    Benefits of feeling younger

    Numerous studies have shown that feeling younger than one’s chronological age is associated with a range of positive outcomes.

    Individuals who feel younger tend to have better physical and mental health, higher levels of life satisfaction, and a more positive outlook on life.

    They are also more likely to engage in healthy behaviors, such as regular exercise and maintaining a balanced diet.

    Impact of subjective age on longevity

    Research suggests that subjective age may even predict longevity. A study published in the Journal of the American Medical Association found that individuals who felt younger than their actual age had a lower risk of mortality compared to those who felt older.

    This finding highlights the potential importance of subjective age as a biophysical marker of aging and its relevance in health assessments.

    Factors influencing subjective age

    Several factors can influence an individual’s subjective age, including:

    • Physical health: Chronic illnesses, disabilities, and poor physical functioning can make people feel older than their chronological age.
    • Mental health: Depression, anxiety, and stress can contribute to feeling older, while positive emotions and a sense of purpose can help individuals feel younger.
    • Social connections: Strong social support and engaging in meaningful relationships can promote a youthful sense of age.
    • Life experiences: Major life events, such as retirement, the loss of a loved one, or becoming a grandparent, can impact how old an individual feels.

    Harnessing the power of subjective aging

    In summary, subjective age is a fascinating concept that has garnered increasing attention from researchers and healthcare professionals alike.

    By understanding the factors that influence subjective age and its potential implications for health and well-being, we can develop strategies to promote a more youthful mindset and improve overall quality of life.

    Encouragingly, recent research on the link between sleep and subjective age suggests that we may have more control over how old we feel than previously thought.

    The full study was published in the journal Proceedings of the Royal Society B Biological Sciences.

    —–

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  • Sleep Health, Sleep Study

    How quality sleep can reduce the risk of heart disease and stroke

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    Original Article | Medical News Today

    • Researchers report that better sleep may translate into a lower risk of cardiovascular disease.
    • They add that consistent and healthy sleep patterns can improve a person’s overall well-being.
    • Experts say people having trouble sleeping should rethink pre-sleep activities and avoid stimulation before bedtime.

    A studyTrusted Source published in the journal JAMA Network Open reports that midlife and older adults with healthy sleep habits have a better chance of avoiding cardiovascular disease.

    Researchers used data collected between 2008 and 2018 from the Dongfeng-Tongji cohortTrusted Source, an ongoing, prospective study in Shiyan, China.

    The research team looked at 15,306 individuals with an average age of 66 years with 58% being female and 42% being male. The researchers reported that 5,474 (36%) people had persistent unfavorable sleep patterns and 3,946 (26%) had persistent favorable sleep patterns.

    The researchers established that 3,669 members of the study group had documented cases of cardiovascular disease during that period, including 2,986 cases of coronary heart disease and 683 cases of stroke over a mean follow-up period of nearly 5 years.

    Compared to people with persistent unfavorable sleep patterns, those with persistent favorable sleep patterns had a significantly lower risk of new onset cardiovascular disease, coronary heart disease, and stroke during the follow-up period.

    Researchers said the genetic risk for cardiovascular disease didn’t modify these associations.

    “However, sleep pattern changes and genetic risk were jointly associated with the [coronary heart disease] and stroke risk in a dose-dependent manner,” the study authors wrote.

    Healthy sleep and heart disease risk 

    The five-year patterns in the study were determined by bedtime, sleep duration, sleep quality, and midday napping as well as polygenic risk scores for coronary heart disease and stroke.

    The participants included people with complete sleep information at the baseline survey from 2008 to 2010 and the first follow-up survey in 2013. Subjects with no history of cardiovascular disease or cancer were prospectively assessed from 2013 to 2018. Scientists performed their statistical analysis in November 2023.

    The authors pointed out cardiovascular disease “is a major cause of morbidity and mortality worldwide. In 2019, cardiovascular deaths accounted for approximately one-third of all deaths globally, including more than 40% of deaths in China.

    The researchers also said that as the cardiovascular disease burden keeps rising in nearly every country, research identifying modifiable risk factors for prevention of serious heart disease is urgent.

    The team acknowledged previous studies have shown an association of sleep with cardiovascular health.

    However, the researchers said most of those studies used only a single measurement, which might not adequately reflect the association of overall sleep with cardiovascular disease as sleep habits may change over time.

    Researchers cited one studyTrusted Source of 9,309 participants living in Europe that indicated that maintaining healthy sleep patterns over a 2-year to 5-year period was associated with a lower risk of cardiovascular disease and coronary heart disease but not stroke.

    However, they noted that the research looked at people in midlife who typically adjusted their sleep patterns around work schedules.

    Lifestyle and genetics also factors in heart health 

    The study authors noted that more research on older, retired people with more natural sleep patterns is still necessary.

    The researchers added that lifestyle and genetic factors are also associated with cardiovascular disease, and previous research has shown people with healthy lifestyles had a lower risk of coronary heart disease and stroke, even among those at high genetic risk.

    “To fill the evidence gap, we collected sleep information at two time points approximately five years apart and prospectively explored the long-term outcomes of changes in sleep patterns on the subsequent incidence of [cardiovascular disease] outcomes among middle-aged and older Chinese retirees,” the study authors wrote. “We further investigated how the five-year changes in sleep patterns interact and combine with [cardiovascular disease]-related genetic variants for the risk of [cardiovascular disease] outcome.”

    Chelsey Borson, a sleep expert and founder of baby sleep consulting service Luna Leaps who was not involved in the study, told Medical News Today that sleep has profound impacts on overall health, including heart health.

    “The link between adequate sleep and heart health is increasingly recognized as vital. Sleep serves as a period of recovery and repair for the heart, reducing stress and inflammation, major risk factors for heart disease,” Borson explained. “It’s not an entirely new idea, but the depth of understanding has deepened significantly in recent years as research has advanced.”

    Borson said studies show people getting fewer than seven hours of sleep per night tend to have higher risks of developing cardiovascular issues such as hypertension, coronary artery disease, and myocardial infarction, which “underscores sleep’s role in regulating blood pressure, heart rate, and cardiovascular stability.”

  • Sleep Health, Sleep Study

    How the Brain Decides Which Memories to Keep Permanent During Sleep

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    Original Article | Sleep Review Magazine

    A new study proposes a mechanism that determines which memories are tagged as important enough to linger in the brain until sleep makes them permanent.

    Summary: A recent study led by NYU Grossman School of Medicine researchers has identified a mechanism through which the brain selects certain memories to become permanent during sleep. Focusing on the hippocampus’s neurons, the study found that “sharp wave-ripples,” brief bursts of intense neuron activity, play a crucial role in this selection process. Memories followed by these ripples during the day are more likely to be replayed and solidified in sleep.

    Brain in Sleep Mode

    Key takeaways: 

    • The study identified “sharp wave-ripples” in the hippocampus as crucial for selecting which daytime memories become permanent during sleep.
    • Daytime events followed by five to 20 sharp wave-ripples are more likely to be consolidated into long-term memories.
    • This process involves the near-simultaneous firing of 15% of hippocampal neurons, encoding complex information within milliseconds.

    Neuroscientists have established in recent decades the idea that some of each day’s experiences are converted by the brain into permanent memories during sleep the same night. 

    Now, a new study proposes a mechanism that determines which memories are tagged as important enough to linger in the brain until sleep makes them permanent.

    Led by researchers from NYU Grossman School of Medicine, the study revolves around brain cells called neurons that “fire”—or bring about swings in the balance of their positive and negative charges—to transmit electrical signals that encode memories. Large groups of neurons in a brain region called the hippocampus fire together in rhythmic cycles, creating sequences of signals within milliseconds of each other that can encode complex information.

    Called “sharp wave-ripples,” these “shouts” to the rest of the brain represent the near-simultaneous firing of 15% of hippocampal neurons and are named for the shape they take when their activity is captured by electrodes and recorded on a graph. 

    While past studies had linked ripples with memory formation during sleep, the new study, published in Science, found that daytime events followed immediately by five to 20 sharp wave-ripples are replayed more during sleep and so consolidated into permanent memories. Events followed by very few or no sharp wave-ripples failed to form lasting memories.

    “Our study finds that sharp wave-ripples are the physiological mechanism used by the brain to ‘decide’ what to keep and what to discard,” says senior study author György Buzsáki, MD, PhD, the Biggs Professor of Neuroscience in the Department of Neuroscience and Physiology at NYU Langone Health, in a release.

    Walk and Pause

    Illustration 175719502 © Viraldhameliya | Dreamstime.com

    The new study is based on a known pattern: Mammals including humans experience the world for a few moments, then pause, then experience a little more, then pause again. After we pay attention to something, say the study authors, brain computation often switches into an “idle” re-assessment mode. Such momentary pauses occur throughout the day, but the longest idling periods occur during sleep.  

    Buzsaki and colleagues had previously established that no sharp wave-ripples occur as we actively explore sensory information or move, but only during the idle pauses before or after. The current study found that sharp wave-ripples represent the natural tagging mechanism during such pauses after waking experiences, with the tagged neuronal patterns reactivated during post-task sleep.

    Importantly, sharp wave-ripples are known to be made up the firing of hippocampal “place cells” in a specific order that encodes every room we enter and each arm of a maze entered by a mouse. For memories that are remembered, those same cells fire at high speed, as we sleep, “playing back the recorded event thousands times per night.” The process strengthens the connections between the cells involved.

    Tracing Memory Formation

    Photo 30816019 © Noam Kahalany | Dreamstime.com

    For the current study, successive maze runs by study mice were tracked via electrodes by populations of hippocampal cells that constantly changed over time despite recording very similar experiences. This revealed for the first time the maze runs during which ripples occurred during waking pauses and then were replayed during sleep.

    Sharp wave-ripples were typically recorded when a mouse paused to enjoy a sugary treat after each maze run. The consumption of the reward, say the authors, prepared the brain to switch from an exploratory to an idle pattern so that sharp wave-ripples could occur.

    Using dual-sided silicon probes, the research team was able to record up to 500 neurons simultaneously in the hippocampus of animals during maze runs. This in turn created a challenge because data becomes exceedingly complex the more neurons are independently recorded. 

    To gain an intuitive understanding of the data, visualize neuronal activity, and form hypotheses, the team successfully reduced the number of dimensions in the data, in some ways like converting a three-dimensional image into a flat one, and without losing the data’s integrity.

    “We worked to take the external world out of the equation, and looked at the mechanisms by which the mammalian brain innately and subconsciously tags some memories to become permanent,” says first author Wannan (Winnie) Yang, PhD, a graduate student in Buzsáki’s lab, in a release. “Why such a system evolved is still a mystery, but future research may reveal devices or therapies that can adjust sharp wave-ripples to improve memory, or even lessen recall of traumatic events.”