Week 3: Sleep and the Brain
How sleep enhances memory and more

How does sleep affect your brain’s health? Specific sleep stages are associated with different types of learning and memory formation. Hormones are involved in helping or hindering sleep.  And sleep comes in cycles, which are useful in determining the best time to sleep and wake.  Our lesson will look into these factors to help you determine the best amount of sleep and some ways to improve your sleep patterns. 

Think of your brain like a busy city that needs quiet time for maintenance. During your waking hours, your brain is constantly working - taking in information, solving problems, controlling movements, and processing emotions. All this activity builds up, and your brain needs sleep to:

·         Clean Up: During sleep, your brain clears out waste products that build up during the day. It's like a night-time cleaning crew sweeping the streets of that busy city.

·         Save Memories: Sleep gives your brain time to sort through what you learned and experienced during the day, storing important information in long-term memory. It's similar to filing away important documents instead of leaving them scattered on your desk.

·         Recharge: Your brain cells use sleep time to repair themselves and prepare for another day of activity. Just like recharging your phone at night, your brain needs this downtime to work well the next day.

·         Process Emotions: While you sleep, your brain works through the day's emotional experiences, helping you cope better with life's ups and downs.

This is why getting good sleep helps you think more clearly, remember better, and feel more emotionally balanced the next day.

Your brain has hormones which are involved in the sleep-wake cycle.  Here are some of them.

Melatonin: The 'Darkness Hormone' 

Melatonin is produced by the pineal gland, a small gland in the center of your brain. It starts increasing in the evening, about 2 hours before bedtime, reaching its peak in the middle of the night (between 2 and 4 AM). This hormone signals that it's time to sleep when darkness falls, acting like your body's internal sunset alarm. Levels stay high through the night and drop in the morning when exposed to light.

GABA (Gamma-Aminobutyric Acid): The 'Relaxation Chemical' 

GABA is released by the hypothalamus and brain stem throughout the night, but it's especially active during the early stages of sleep. This calming chemical helps quiet brain activity and relax your muscles, working like your brain's "quiet down" signal. It's particularly important in those first few hours of sleep when your body is transitioning from wakefulness to deep sleep.

Adenosine: The 'Sleep Pressure' Builder 

Adenosine builds up in your basal forebrain gradually throughout your waking hours. The longer you stay awake, the more adenosine accumulates, making you feel increasingly sleepy. Levels are lowest in the morning after a good night's sleep and highest right before bedtime. When you sleep, adenosine levels decrease, which is why you feel refreshed in the morning. This is also why caffeine keeps you awake - it blocks adenosine from doing its job!

Growth Hormone: The 'Repair Hormone' 

Growth hormone is released by the pituitary gland primarily during the first few hours of sleep, especially during deep sleep stages. The largest surge occurs about an hour after you fall asleep, with smaller pulses throughout the night. This hormone works like your body's nighttime maintenance crew, helping to repair and restore your body while you sleep.

Cortisol: The 'Wake-Up Hormone' 

While cortisol is made by the adrenal glands, it's controlled by the hypothalamus. Its levels are lowest around midnight and start rising in the early morning hours, peaking just before you wake up (usually around 8 AM). This natural pattern helps you feel alert and ready to start your day, working as your body's natural morning alarm clock. Levels then gradually decline throughout the day, helping to maintain your normal sleep-wake cycle."

Activity:  We will do a Zoom quiz showing a hormone and asking whether it helps you to sleep or to wake up.

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.

Understanding Your Sleep Cycles: The 90-Minute Rule

As we look at how the brain regulates sleep, it's important to understand that sleep follows a rhythmic pattern. One commonly discussed concept is the 90-minute sleep cycle, which is based on research into the stages of sleep.

However, it’s important to note that this 90-minute cycle is an approximation. Sleep cycles vary from person to person and can even differ slightly from night to night. For most people, the cycle ranges between 70 to 110 minutes. This variability is normal and influenced by factors like age, health, and sleep quality.

As discussed earlier, during each sleep cycle, the brain transitions through different stages:

1. Light Sleep (non rem Stage 1): The body starts to relax.

2. Deeper Relaxation (non rem Stage 2): Heart rate slows, and body temperature drops.

3. Deep Sleep (non rem Stage 3): This stage is essential for body restoration.

4. REM Sleep: The dreaming stage, where the brain becomes highly active.

On an average night, a person may complete 4 to 6 cycles, moving through these stages in a recurring pattern. This rhythmic cycling helps the brain and body perform critical functions, like memory consolidation, emotional processing, and physical repair.

While the 90-minute rule is often used as a guide for planning sleep schedules or naps, it’s not a strict rule set in stone. Think of it as a helpful framework, not an exact science, since your personal sleep rhythm may be slightly shorter or longer.

1. Practice the "Memory and Sleep Connection"

   • Try learning important things in the evening before bed

   • For example, if you're learning a new card game, practice it before bedtime

   • Review important information like appointment times before sleeping

   • If you're learning new technology, practice in the evening and let sleep help cement the steps

2. Create a "Memory-Friendly" Sleep Routine

   • Go to bed at the same time each night

   • Avoid looking at phones or tablets an hour before bed

   • Try reading something you want to remember during this quiet time

   • Keep your bedroom cool, dark, and quiet

3. Use the "Morning Review"

   • In the morning, try to recall what you learned the night before

   • Notice how details are often clearer after sleep

   • Practice any new skills you learned yesterday

   • Write down important memories from the day before

4. Time Your Learning

   • Schedule challenging activities (like learning new technology) when you're well-rested

   • Take a short nap after learning something new if you can

   • Important appointments? Get good sleep the night before

   • Try to learn complex things in the evening before sleep, rather than first thing in the morning

Remember: Just like a phone needs recharging, your brain needs good sleep to store memories properly. Even a simple nap can help lock in new information. So the next time you're learning something new, make sure to follow it up with good sleep.  Your memory will thank you!"

In today’s class, we looked at sleep.  We learned why sleep is so important to the brain and discussed the several stages.  We learned how to tell if we have adequate sleep, and included ways to improve your memory while sleeping, as well as tips for quality sleep.  Use this information to improve your own sleep.  Let us know what worked.

If you want to dive deeper in to the world of sleep, here are some great resources.  

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

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

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