Week 11: Sleep and the brain
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Video: Our Wednesday night class planned to do this, but we ran out of time. Nice meditation to help sleep!
Sleep and the Brain
How does sleep affect your brain’s health? Specific sleep stages are associated with different types of learning and memory formation. We examine the anatomy of sleep and will uncover how each phase of the sleep cycle restores and rejuvenates the brain for optimal function.
Sleep is a basic human need, like food, water, and oxygen. And, just like these other needs, sleep is vital for our health and well-being. There are many parts of the brain that play a role in the sleep cycle.
Video: This video provides an overview of o ur lesson, what happens when we sleep and how our brain adapts.
Anatomy of Sleep
The hypothalamus contains groups of nerve cells that act as control centers affecting sleep and arousal. Within the hypothalamus is the suprachiasmatic nucleus (SCN) – clusters of thousands of cells that receive information about light exposure directly from the eyes and control your behavioral rhythm.
The brain stem communicates with the hypothalamus to control the transitions between wake and sleep. The brain stem includes structures called the pons, medulla, and midbrain. Sleep-promoting cells within the hypothalamus and the brain stem produce a brain chemical called GABA, which acts to reduce the activity of arousal centers in the hypothalamus and the brain stem. In other words, GABA is associated with sleep, muscle relaxation, and sedation. The brain stem (especially the pons and medulla) also plays a special role in Rapid Eye Movement (REM) sleep; it sends signals to relax muscles, so that we don’t act out our dreams.
The thalamus acts as a relay for information from the senses to the cerebral cortex, which plays a role in how we interpret and process information from short- to long-term memory. During most stages of sleep, the thalamus becomes quiet, letting you tune out the external world. But during REM sleep, the thalamus is active, sending the cortex images, sounds, and other sensations that fill our dreams.
The pineal gland receives signals from the SCN and increases production of the hormone melatonin, which helps put you to sleep once the lights go down. Scientists believe that peaks and valleys of melatonin over time are important for matching the body’s circadian rhythm to the external cycle of light and darkness.
The basal forebrain also promotes sleep and wakefulness, while part of the midbrain acts as an arousal system. Release of adenosine from cells in the basal forebrain supports your sleep drive. Interesting fact: Caffeine counteracts sleepiness by blocking the actions of adenosine.
The amygdala is involved in processing emotions and becomes increasingly active during REM sleep.
Sleep and Wakefulness in the brain (Source)
Sleep-Wake hormones
Melatonin:
When it gets dark, your body releases a hormone called melatonin. Melatonin signals your body that it's time to prepare for sleep, and it helps you feel sleepy. The amount of melatonin in your bloodstream peaks as the evening passes. Researchers believe this peak is an important part of preparing your body for sleep. Exposure to bright artificial light, from a TV screen, computer screen, bright alarm clock, mobile phone etc., late in the evening can disrupt this process, making it hard to fall asleep.
Cortisol:
As the sun rises, your body releases cortisol. This hormone naturally prepares your body to wake up.
Sleep Stages
There are two basic types of sleep: rapid eye movement (REM) sleep and non-REM sleep. REM and non-REM sleep are both linked to specific brain waves and neuronal activity. During a typical night, you cycle through all stages of non-REM and REM sleep several times, with increasingly longer, deeper REM periods occurring toward morning. The cycle starts over every 80 to 100 minutes. There are usually four to six cycles per night and you may wake up briefly between cycles.
Stage 1, non-REM sleep, is the changeover from wakefulness to sleep. This is a short period (lasting several minutes) of relatively light sleep when your heartbeat, breathing, and eye movements slow down, and your muscles relax with occasional twitches. Your brain waves begin to slow from their daytime wakefulness patterns.
Stage 2, non-REM sleep, is a period of light sleep before you enter deeper sleep. Your heartbeat and breathing slow, and muscles relax even further. Your body temperature drops and eye movements stop. You spend more of your repeated sleep cycles in stage 2 sleep than in other sleep stages
Stage 3, non-REM sleep, is the period of deep sleep that you need to feel refreshed in the morning. It occurs in longer periods during the first half of the night. Your heartbeat and breathing slow to their lowest levels during sleep. Your muscles are relaxed and it may be difficult to awaken you.
REM sleep first occurs about 90 minutes after falling asleep. Your eyes move rapidly from side to side behind closed eyelids. Mixed frequency brain wave activity becomes closer to that seen in wakefulness. Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels. Most of your dreaming occurs during REM sleep, although some can also occur in non-REM sleep. Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams. As you age, you sleep less of your time in REM sleep. Memory consolidation most likely requires both non-REM and REM sleep.
Video: A closer look at the four stages of sleep and how the brain and body adapt.
4 stages of sleep (Source)
Sleep Mechanisms
Two internal biological mechanisms–circadian rhythm and homeostasis–work together to regulate when you are awake and sleep.
Circadian rhythms direct a wide variety of functions such as wakefulness, body temperature, metabolism, and the release of hormones. They control your timing of sleep and cause you to be sleepy at night and your tendency to wake in the morning without an alarm. Your body’s biological clock, which is based on a roughly 24-hour day, controls most circadian rhythms. Circadian rhythms synchronize with environmental cues (e.g., light, temperature) about the actual time of day, but they continue even in the absence of cues.
Wake/Sleep cycle showing sleep homeostasis and circadian alerting (source)
Video: This video describes the 2-process model which includes sleep homeostasis and circadian rhythms
Two processes interact to control the circadian rhythm.
The first is a pressure to sleep that builds with every hour that you're awake. This drive for sleep peaks in the evening when most people fall asleep. Adenosine is one factor linked to this drive for sleep. The increasing level of adenosine signals a shift toward sleep. While you sleep, your body breaks down adenosine.
A second process involves your internal body clock. This clock is in sync with certain cues in the environment. Light, darkness, temperature and other cues help determine when you feel awake and when you feel sleepy.
Sleep-wake homeostasis keeps track of your need for sleep. The homeostatic sleep drive reminds the body to sleep after a certain time and regulates sleep intensity. This sleep drive gets stronger every hour you are awake and causes you to sleep longer and more deeply after a period of sleep deprivation.
Factors that influence your sleep-wake needs include medical conditions, medications, stress, sleep environment, activity, and what you eat and drink. Perhaps the greatest influence is the exposure to light. Specialized cells in the retinas of your eyes process light and tell the brain whether it is day or night and can advance or delay our sleep-wake cycle. Exposure to light can make it difficult to fall asleep and return to sleep when awakened.
Factors influencing sleep (source)
Changes in the body clock with aging
The rhythm and timing of the body clock change with age. Teens fall asleep later at night than younger children and adults. One reason for this is because melatonin is released and peaks later in the 24-hour cycle for teens. As a result, it's natural for many teens to prefer later bedtimes at night and sleep later in the morning than adults.
People also need more sleep early in life when they're growing and developing. For example, newborns may sleep more than 16 hours a day, and preschool-age children need to take naps. Young children tend to sleep more in the early evening. Teens tend to sleep more in the morning. Older adults tend to go to bed earlier and wake up earlier.
The patterns and types of sleep also change as people mature. For example, newborn infants spend more time in REM (rapid eye movement) sleep. Dreaming typically occurs during REM sleep. The amount of deep or slow-wave sleep (non-REM sleep) peaks in early childhood and then drops sharply after puberty. It continues to decline as people age. Slow-wave sleep continues to decrease through adulthood, and older people may not have any slow-wave sleep at all.
Video: Changes in sleep as we age
Sleep may improve the ability to learn
When learning facts and information, most of what we learn is temporarily stored in a region of the brain called the hippocampus. Some scientists hypothesize that, like most storage centers, the hippocampus has limited storage capacity. So, if the hippocampus is full, we won’t be able to learn any more information.
Many scientists also hypothesize that sleep, particularly Stages 2 and 3 sleep, plays a role in replenishing our ability to learn. In one study, a group of 44 participants underwent two rigorous sessions of learning, once at noon and again at 6:00 PM. Half of the group was allowed to nap between sessions, while the other half took part in standard activities. The researchers found that the group that napped between learning sessions learned just as easily at 6:00 PM as they did at noon. The group that didn’t nap, however, experienced a significant decrease in learning ability (Mander at al., 2011).
Sleep may improve the ability to recall information
Humans have known about the benefits of sleep for memory recall for thousands of years. Scientists have tested this theory many times, often finding that sleep improves memory retention and recall by between 20 and 40%. Research has led scientists to hypothesize that Stage 3 (deep non-Rapid Eye Movement sleep, or Slow Wave Sleep) may be especially important for the improvement of memory retention and recall (Walker et al., 2009).
Benefit of sleep to recall information (source)
Sleep may improve long-term memory
Long term memory formation sleep vs wake (source)
Scientists hypothesize that sleep also plays a major role in forming long-term memories. According to Matthew Walker, professor of neuroscience and psychology at UC Berkeley, MRI scans indicate that the slow brain waves of stage 3 sleep (deep NREM sleep) “serve as a courier service,” transporting memories from the hippocampus to other more permanent storage sites (Walker et al., 2017).
Sleep may improve the ability to solve problems creatively
Many tests are designed to assess critical thinking and creative problem-solving skills. Scientists hypothesize that sleep, particularly REM sleep, plays a role in strengthening these skills. In one study, scientists tested the effect of REM sleep on the ability to solve anagram puzzles (word scrambles like “EOUSM” for “MOUSE”), an ability that requires strong creative thinking and problem-solving skills.
In the study, participants solved a couple of anagram puzzles before going to sleep in a sleep laboratory with electrodes placed on their heads. The subjects were woken up four times during the night to solve anagram puzzles, twice during Non REM sleep and twice during REM sleep.
The researchers found that when participants were woken up during REM sleep, they could solve 15 to 35% more puzzles than they could when woken up from Non REM sleep. They also performed 15 to 35% better than they did in the middle of the day (Walker et al., 2002). It seems that REM sleep may play a major role in improving the ability to solve complex problems.
Sleep can help you to solve problems! (source)
How much sleep do I need?
Older adults need a similar amount of sleep as all adults—7 to 9 hours on average each night. As you age, it is common to take longer to fall asleep and have more awakenings in the night. Difficulty staying asleep for the entire night is ok if you can fall back to sleep, but quality and quantity are both important.
According to the Centers for Disease Control and Prevention
● about 1 in 3 adults in the United States reported not getting enough rest or sleep every day
● nearly 40% of adults report falling asleep during the day without meaning to at least once a month
● an estimated 50 to 70 million Americans have chronic, or ongoing, sleep disorders
Sleep deficiency can lead to physical and mental health problems, injuries, loss of productivity, and even a greater likelihood of death.
What is Sleep deficiency?
Sleep deprivation occurs when we do not get enough sleep. And that can lead to sleep deficiency when combined with sleeping during the day, not sleeping well, little deep or restorative sleep, and sleep disorders. It occurs if you have one or more of the following:
● You don't get enough sleep (sleep deprivation)
● You sleep at the wrong time of day
● You don't sleep well or get all the different types of sleep your body needs
● You have a sleep disorder that prevents you from getting enough sleep or causes poor-quality sleep
You might be sleep deficient if you often feel like you could doze off while (signs and symptoms):
● Sitting and reading or watching TV
● Sitting still in a public place, such as a movie theater, meeting, or classroom
● Riding in a car for an hour without stopping
● Sitting and talking to someone
● Sitting quietly after lunch
● Sitting in traffic for a few minutes
Sleep deficiency can interfere with work, school, driving, and social functioning. You might have trouble learning and focusing. Your reaction time might be slower. Sleep deficiency also can make you feel frustrated, cranky, or worried in social situations. You might find it hard to judge other people's emotions and reactions.
Sleep deficiency is linked to a higher chance of injury in adults, teens, and children. In older adults, sleep deficiency comes with an increased risk of physical and mental health problems and higher rates of accidents and injuries.
Effects of sleep deprivation to brain and body (source)
Video: What are the effects of sleep deprivation?
Sleep and chronic disease
Sleep has been linked to the development and management of a number of chronic diseases and conditions, including type 2 diabetes, cardiovascular disease, and depression.
Diabetes
Research has found that insufficient sleep is linked to an increased risk of type 2 diabetes. Specifically, sleep duration and quality have emerged as predictors of levels of Hemoglobin A1c, a marker of blood glucose control. Research suggests that optimizing sleep duration and quality may be important means of improving blood glucose control in persons living with type 2 diabetes (Knutson et al., 2006)
Cardiovascular Disease
Persons with sleep apnea have been found to be at increased risk for a number of cardiovascular diseases. Notably, hypertension, stroke, coronary heart disease and irregular heartbeats (cardiac arrhythmias) have been found to be more common among those with disordered sleep. Likewise, sleep apnea and hardening of the arteries (atherosclerosis) appear to share some common physiological characteristics, further suggesting that sleep apnea may be an important predictor of cardiovascular disease (Kasasbeh et al., 2006)
Depression
The relationship between sleep and depression is complex. While sleep disturbance has long been held to be an important symptom of depression, research has indicated that depressive symptoms may decrease once sleep apnea has been effectively treated and sufficient sleep restored. The interrelatedness of sleep and depression suggests it is important that individuals with depression be assessessed for sleep deficiency and vice versa (Zimmerman et al., 2006; Schwartz et al., 2005)
Frequency of sleep disorders in medical conditions (source)
Mental health benefits of Sleep
Sleep helps your brain work optimally. While you're sleeping, your brain is getting ready for the next day. It's forming new pathways to help you learn and remember information, problem solve and form memories. Sleep also helps you pay attention, make decisions, and be creative.
Studies show that sleep deficiency changes activity in some parts of the brain. If you're sleep deficient, you may have trouble making decisions, solving problems, controlling your emotions and behavior, and coping with change.
Physical health benefits of Sleep
Sleep plays an important role in your physical health, overall health and well-being. Sleep affects our hormones, metabolism, breathing, immune system, thinking, and memory. Specifically, good-quality sleep:
● Heals and repairs your heart and blood vessels.
● Helps support a healthy balance of the hormones that make you feel hungry (ghrelin) or full (leptin): When you don't get enough sleep, your level of ghrelin goes up and your level of leptin goes down. This makes you feel hungrier than when you're well-rested.
● Affects how your body reacts to insulin: Insulin is the hormone that controls your blood glucose level. Sleep deficiency results in a higher-than-normal blood sugar level, which may raise your risk of diabetes.
● Supports healthy growth and development: Deep sleep triggers the body to release the hormone that promotes normal growth in children and teens. This hormone also boosts muscle mass and helps repair cells and tissues in children, teens, and adults. Sleep also plays a role in puberty and fertility.
● Affects your body’s ability to fight germs and sickness: Ongoing sleep deficiency can change the way your body’s natural defense against germs and sickness responds. For example, if you're sleep deficient, you may have trouble fighting common infections.
● Decreases your risk of health problems, including heart disease, high blood pressure, obesity, and stroke.
Benefits of sleep (source)
How to establish healthy sleep habits
Here are some top tips for establishing better sleep habits:
● Establish a ritual for winding down before going to bed. Relax before bed – try a warm bath, reading, or another relaxing routine. Try journaling before bed or listening to relaxing music.
● Limit light exposure from digital technology late in the evening and refrain from social media or any type of upsetting news coverage, too. Go to bed and get up at the same time every day. Following an established bedtime routine can prevent any interruptions to your circadian rhythm that could lead to sleep problems.
● Set your bedtime when you are able to get seven to eight hours of sleep. Plan your nightly routine so you will be sleepy and go to bed with time for adequate rest before your wakeup time.
● Limit certain foods and drinks before bedtime. Alcohol and sleep aids are not good ideas because they can be more likely to cause sleep disturbances. Avoid large, heavy meals before bed and stay away from caffeine in the afternoons which can stay in your system for as long as 10-12 hours and keep you awake at night.
● Engage in daily activities that nourish you. Connect and visit with family and friends. When it is not possible to have in-person visits due to social distancing practices, reach out using the telephone and through video calls, or send emails, cards and hand-written letters.
● Be physically active every day and get outside. Exercise early in the day to bolster your mood and help you get the natural sunlight you need, signaling to your brain that it is daytime and establish a rhythm of your sleep and wake cycle.
● Don’t go to bed if you’re not sleepy. Going to bed when you are not sleepy can result in frustration with not being able to go to sleep, and this frustration can make it even harder to get to sleep. If you can’t get to sleep, do something else, like reading or listening to music, until you feel tired.
● Don’t worry if you wake up during the night. If it takes more than 15-20 minutes to fall back to sleep, get out of bed and try reading or listening to soft music for a little while until you feel sleepy. Then try again. Do not use electronics at this time.
● Reserve your bedroom as a place for sleep. The goal is to associate the bedroom and bed with sleep and intimacy. Avoid eating or working in your bedroom.
● Set a quiet and relaxing atmosphere for sleep, including a comfortable temperature. Your sleep environment should be as relaxing and comforting as possible to maximize your sleep success. If you are able to, keep out TVs, tablets, smart phones, and computers.
Tips for better sleep (source)
Summary
Sleep is a basic human need, like food, water, and oxygen. And, just like these other needs, sleep is vital for optimal brain function, our overall health and well-being. There are many things you can do to establish good sleep habits such as limiting light exposure at night and establishing a nighttime ritual to help you feel relaxed before bed. If you feel unusually tired during the day and/or have problems sleeping, please see a doctor. Many sleep disorders can be treated effectively.
References
National Institute of Neurological Disorders and Stroke of the NIH. Brain Basics: Understanding Sleep. Retrieved from https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep. Accessed on April 10, 2024
National Heart, Lung and Blood Institute of the NIH. Sleep Phases and Stages. Retrieved from https://www.nhlbi.nih.gov/health/sleep/stages-of-sleep. Accessed on April 10, 2024
National Heart, Lung and Blood Institute of the NIH. What makes you sleep? Retrieved from https://www.nhlbi.nih.gov/health/sleep-deprivation/body-clock. Accessed on April 10, 2024
Centers for Disease Control and Prevention. Retrieved from https://archive.cdc.gov/www_cdc_gov/media/releases/2016/p0215-enough-sleep.html, Accessed on April 10, 2024
National Heart, Lung and Blood Institute of the NIH. What Are Sleep Deprivation and Deficiency? Retrieved from https://www.nhlbi.nih.gov/health/sleep-deprivation. Accessed on April 10, 2024
National Heart, Lung and Blood Institute of the NIH. How Sleep Affects Your Health. Retrieved from https://www.nhlbi.nih.gov/health/sleep-deprivation/health-effects. Accessed on April 10, 2024
Perelman School of Medicine at the University of Pennsylvania. The Impact of Sleep on Learning and Memory. Retrieved from https://www.med.upenn.edu/csi/the-impact-of-sleep-on-learning-and-memory.html. Accessed on April 10, 2024
Centers for Disease Control and Prevention. Sleep and Chronis Disease. Retrieved from https://www.cdc.gov/sleep/about_sleep/chronic_disease.html. Accessed on April 10, 2024
National Council on Aging. How Sleep Impacts the Top-Age Related Health Concerns. Retrieved from https://www.ncoa.org/adviser/sleep/chronic-conditions-and-sleep/ Accessed on April 10, 2024
National Council on Aging. How Sleep Affects Your Health. Retrieved from https://www.ncoa.org/article/how-sleep-affects-your-health. Accessed on April 10, 2024
Mander, Bryce A., et al. “Wake Deterioration and Sleep Restoration of Human Learning.” Current Biology, vol. 21, no. 5, 2011, doi:10.1016/j.cub.2011.01.019.
Walker M. P. (2009). The role of slow wave sleep in memory processing. Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine, 5(2 Suppl), S20–S26.
Walker, Matthew. Why We Sleep. Scribner, 2017.
Walker, Matthew P, et al. “Cognitive Flexibility across the Sleep–Wake Cycle: REM-Sleep Enhancement of Anagram Problem Solving.” Cognitive Brain Research, vol. 14, no. 3, 2002, pp. 317–324., doi:10.1016/s0926-6410(02)00134-9.
Knutson KL, Ryden AM, Mander VA, Van Cauter E. Role of sleep duration and quality in the risk and severity of type 2 diabetes mellitus. Arch Intern Med 2006;166:1768–1764.
Kasasbeh E, Chi DS, Krishnaswamy G. Inflammatory aspects of sleep apnea and their cardiovascular consequences. South Med J 2006;99:58–67.
Zimmerman M, McGlinchey JB, Young D, Chelminski I. Diagnosing major depressive disorder I: A psychometric evaluation of the DSM-IV symptom criteria. J Nerv Ment Dis 2006;194:158–163.
Schwartz DJ, Kohler WC, Karatinos G. Symptoms of depression in individuals with obstructive sleep apnea may be amenable to treatment with continuous positive airway pressure. Chest 2005;128:1304–1306.