Sleep Architecture: Understanding Rem Sleep's Role

Sleep is a complex and dynamic process that affects how you function in ways scientists are now beginning to understand. Sleep is an important part of your daily routine—you spend about one-third of your time doing it. Quality sleep—and getting enough of it at the right times—is as essential to survival as food and water. Without sleep, you can’t form or maintain the pathways in your brain that let you learn and create new memories. Lack of sleep makes it harder to concentrate and respond quickly.

Sleep is made up of two different types: rapid eye movement (REM) sleep and non-REM sleep. Throughout your time asleep, your brain will cycle repeatedly through these two types of sleep. The first part of the cycle is non-REM sleep, which is composed of four stages. The first stage comes between being awake and falling asleep. The second is light sleep, when heart rate and breathing regulate and body temperature drops. The third and fourth stages are deep sleep. As you cycle into REM sleep, the eyes move rapidly behind closed lids, and brain waves are similar to those during wakefulness. Breath rate increases and the body becomes temporarily paralyzed as we dream.

REM sleep and the brain

REM sleep is one of two types of sleep, the other being non-REM sleep. During REM sleep, the eyes move rapidly in different directions, and the brain is active. Brain activity during REM sleep is similar to its activity when awake. Dreams typically happen during REM sleep.

REM sleep typically starts within 90 minutes of falling asleep. As the sleep cycle repeats, REM sleep occurs several times while a person is resting. In fact, it accounts for approximately 20–25% of an adult’s sleep cycle and over 50% of an infant’s.

During REM sleep, the body and brain go through several changes, including:

• Rapid movements of the eyes
• Fast and irregular breathing
• Increased heart rate (to near waking levels)
• Changes in body temperature
• Increased blood pressure
• Brain activity (similar to waking levels)
• Increased oxygen consumption by the brain
• Twitching of the face and limbs

Most people experience a state of temporary paralysis as the brain signals the spinal cord to cease the movement of the arms and legs. This lack of muscle activity is known as atonia, and it may be a protective mechanism to prevent injury that may result from “acting out” our dreams.

REM sleep may benefit learning, memory, and mood. A lack of REM sleep may have adverse implications for physical and mental health.

The brain processes information and consolidates memories during sleep. As a result, sleep deprivation can negatively affect a person’s working memory.

REM sleep may be essential for brain development in infants. Some research indicates that this sleep stage is responsible for the neural stimulation necessary for mature brain structure developments.

REM Sleep and Memory

REM sleep is the stage of sleep where most dreams happen. Its name comes from how your eyes move behind your eyelids while you’re dreaming. During REM sleep, your brain activity looks very similar to brain activity while you’re awake.

REM sleep makes up about 25% of your total time asleep. Your first REM cycle of a sleep period is typically the shortest, around 10 minutes. Each of your later REM stages gets longer, and the final one may last up to an hour.

REM sleep is important because it stimulates the areas of your brain that help with learning and memory. During this stage, your brain repairs itself and processes emotional experiences. It also transfers short-term memories into long-term memories.

REM sleep is associated with a reduction in acetylcholine levels, which are high during wakefulness. This reduction in acetylcholine levels enables the consolidation of memories during sleep.

REM sleep is associated with a decrease in the release of cortisol, which is a stress hormone. This reduction in cortisol levels during REM sleep benefits the consolidation of declarative memories.

Non-REM sleep and the brain

Non-REM sleep is an essential part of the sleep cycle, consisting of three stages: N1, N2, and N3, with N3 being the deepest. Non-REM sleep stages are vital for physical and mental restoration.

During non-REM sleep, your brain is not as active as it is during REM sleep. In the deeper stages of non-REM sleep, your breathing slows down, and your blood pressure drops. Your body temperature also drops during this time.

As you cycle through the three stages of non-REM sleep, various bodily functions slow down or stop altogether, allowing for repair and restoration. The first stage, N1, is when your heartbeat, eye movements, brain waves, and breathing activity begin to slow down. Motor movements also diminish, although you may experience muscle twitches called hypnic jerks. This stage usually only lasts a few minutes.

In the second stage, N2, there is a continued slowing of heartbeat, breathing, muscle activity, and eye movements. This is also when your body temperature drops. Brain waves generally slow down further, and two unique types of brain activity may occur: sleep spindles and K-complexes. Sleep spindles are short bursts of brain activity that are essential for memory and learning and help block out external stimuli so you don't wake up as easily. K-complexes may also help keep you asleep by blocking reactions to harmless stimuli, but they can also help wake you up if your brain perceives a stimulus as dangerous.

The third stage, N3, is the deepest stage of sleep, also known as slow-wave sleep. Your heartbeat, breathing, muscle activity, and brain waves are at their slowest during this stage. The body releases growth hormones and carries out tissue, muscle, and bone repair. Deep sleep is thought to help regulate glucose metabolism, immune system functioning, hormone release, and memory. Most people obtain the bulk of their deep sleep at the beginning of the night. Without enough slow-wave sleep, you may wake up feeling unrefreshed.

Non-REM sleep is important for both physical growth and repair and memory consolidation. Studies have shown that sleep disorders that interrupt sleep may interfere with fat metabolism and impact levels of growth hormone, creating a vicious cycle. Non-REM sleep may also impact the cardiovascular system, as blood pressure drops during slow-wave sleep, which is thought to play a protective role against heart disease.

During non-REM sleep, the brain consolidates new memories and skills into a more durable format and optimizes mental pathways for future learning. Specific patterns during non-REM sleep are associated with better working memory, verbal fluency, motor learning, and word retrieval. Non-REM sleep is thought to play a role in both declarative memory (the ability to recall information) and procedural memory (the ability to learn new tasks). One theory is that sleep spindles help strengthen neural connections related to recently acquired memories, and then slow-wave sleep tidies up the pathways so they are ready for use the next day.

The relationship between sleep and memory

Sleep and memory are intricately linked. The process of memory consolidation, which involves preserving key memories and discarding unimportant information, occurs during both the non-rapid eye movement (NREM) and rapid eye movement (REM) stages of the sleep cycle.

During the NREM stages, the brain sorts through memories from the day, deciding which ones to keep and which to eliminate. These selected memories are then further solidified during the deep NREM sleep stage, before being linked to existing memories during the REM stage. Dreaming mostly occurs during REM sleep, and the thalamus of the brain transmits cues from our senses to the cerebral cortex, which then integrates this information into our dreams. The REM stage is also when emotional memories are processed, which can help us cope with challenging experiences.

Research suggests that a good night's sleep helps strengthen memories formed throughout the day and facilitates the creation of connections between new and existing memories. Sleep before learning can improve our ability to form new memories, and sleep after learning helps to cement new information into our brains, making it easier to recall.

The quality and quantity of sleep both play a role in memory consolidation. Insufficient or poor-quality sleep can negatively impact memory processing and other cognitive functions. Sleep deprivation can lead to difficulties in remembering, learning, focusing, and controlling emotions and behaviour. On the other hand, excessive sleep can also impair cognitive functions. Therefore, it is essential to strive for the optimal amount of sleep, which is typically 7 to 9 hours for adults.

The role of genes and neurotransmitters in sleep

Sleep is a complex and mysterious body process that remains largely undiscovered by modern medicine. However, it is known that the process is controlled by the release of certain neurotransmitters in the brain.

Neurotransmitters are chemicals that send messages to nerve cells in the brain. During sleep, nerve cells in the brainstem release neurotransmitters such as norepinephrine, histamine, and serotonin. These neurotransmitters act on parts of the brain to keep it alert and functioning while you are awake.

Gamma-aminobutyric acid (GABA) is the most common inhibitory transmitter in the brain. GABAergic cells induce sleep by inhibiting cells that are involved in arousal functions. Cholinergic neurons in the basal forebrain are directly inhibited by GABAergic sleep-active neurons. Since the cholinergic system is one of the main forebrain arousal systems of the brain, the inhibition produced by this activity deactivates the cortex.

Hypocretin, also called orexin, was discovered in 1998, and its role in sleep and narcolepsy was identified in 2001. Hypocretin can cause the release of the amino acid glutamate. Applying hypocretin to trigeminal motor neurons causes excitation, but only in the presence of glutamate. If glutamate receptors are blocked, hypocretin does not activate the motor neurons.

The hypothalamus is the part of the brain most important in regulating sleep duration. The anterior hypothalamus and basal forebrain contain sleep-active neurons, while the posterior hypothalamus contains wake neurons.

Adenosine is a chemical that induces sleepiness. Caffeine promotes wakefulness by blocking the receptors to adenosine.

Other neurotransmitters, such as acetylcholine, can help your brain keep information gathered while you are awake. It then sets that information as you sleep. So if you study or learn new information in the hours before bed, "sleeping on it" can help you remember it.

Abnormalities with the neurotransmitter dopamine may trigger sleep disorders such as restless legs syndrome.

Tips for getting a good night's sleep

Keep in Sync with Your Body's Sleep-Wake Cycle

Keeping a regular sleep-wake schedule is one of the most important strategies for achieving good sleep. Aim to go to sleep and wake up at the same time every day, even on weekends. This helps set your body's internal clock and optimises your sleep quality. Choose a bedtime when you normally feel tired, and avoid sleeping in, as altering your sleep schedule by even an hour or two can negatively impact your energy levels.

Control Your Exposure to Light

Melatonin is a hormone that regulates your sleep-wake cycle by making you feel sleepy when it's dark and more alert when it's light. To maintain healthy melatonin levels, expose yourself to bright sunlight in the morning and spend more time outside during daylight. Let natural light into your home, and if possible, work near a window. Avoid bright screens within 1-2 hours of bedtime, and keep your bedroom dark when you sleep.

Exercise During the Day

Exercising regularly helps you fall asleep faster and improves your sleep quality. Vigorous exercise has the most benefits, but even light exercise, such as a 10-minute walk, can improve sleep. Just be sure to finish moderate to vigorous workouts at least three hours before bedtime, as exercising too close to bed can interfere with sleep.

Be Smart About What You Eat and Drink

Your daytime eating habits impact your sleep, especially in the hours before bedtime. Focus on a heart-healthy diet rich in vegetables, fruit, and healthy fats, with limited amounts of red meat. Cut back on sugary foods and refined carbs, as these can disrupt your sleep. Avoid caffeine and nicotine, as these stimulants can affect your sleep up to 12 hours after consumption. Also, limit alcohol, heavy meals, and liquids close to bedtime to prevent indigestion and reduce the risk of frequent bathroom trips during the night.

Improve Your Sleep Environment

Creating a peaceful bedtime routine signals to your brain that it's time to wind down. Keep your bedroom dark, cool, and quiet. Use earplugs, fans, or sound machines to block out noise if needed. Make sure your bed is comfortable, and your bed covers allow you to stretch and turn easily. Reserve your bed for sleeping and sex, so your brain associates the bedroom with relaxation.

Wind Down and Clear Your Head

Residual stress, worry, and anger can make it difficult to fall asleep. Manage your stress levels and curb the worry habit to improve your sleep. Develop a relaxing bedtime ritual, such as practising relaxation techniques, taking a warm bath, or listening to soft music. Limit screen time before bed, and set specific times during the day for checking your phone and social media to help calm your mind at bedtime.

Learn How to Get Back to Sleep

If you wake up during the night, try not to stress about falling back asleep. Focus on your body or practice breathing exercises, such as deep belly breathing. Make relaxation your goal, and try techniques like visualisation, progressive muscle relaxation, or meditation. If you've been awake for more than 15 minutes, get up and do a quiet, non-stimulating activity in dim light, such as reading a book.

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