Chapter 1: What Sleep Does

Chapter Introduction

The room is dim.

You are lying down. Your eyes are starting to close. Your breath has gotten slow without you noticing. Somewhere outside, a streetlight is on. A neighbor's dog has stopped barking. A clock is ticking. Maybe a parent or sibling is brushing teeth in another room. Maybe the house is already quiet.

Hi. I am the Cat.

We have met before. Twice now.

If you read my G3 chapter — Your Sleep and You — you already know that sleep is not "off." You know your brain stays busy at night doing different work. You know sleep helps your body grow and helps your brain save what you learned. You know that when sleep gets hard, you tell a trusted grown-up.

If you read my G4 chapter — How Sleep Works — you also know that sleep has parts. Deep sleep does body work. Dream sleep does brain work. The parts come around and around through the night in cycles, each cycle about ninety minutes. You know that dreams happen because your brain is sorting things out. You know that babies and kids and teens and grown-ups all need different amounts of sleep, and that sleep changes across a whole life.

Welcome back. The Cat is glad to see you again. The Cat curls up beside you, eyes half-closed, purring softly. There is no hurry. We have time.

You are ten or eleven years old now. You are bigger than you were at G3. You have slept hundreds of nights since we last talked. Maybe you have started to notice things about sleep you did not notice before — that staying up late one night makes the next day feel harder, that your mood is different on days you slept well versus days you did not, that some weeks sleep is easy and some weeks it is not. You are ready for the next step.

This chapter has three big ideas, and each one builds on what you already know.

The first big idea is what sleep actually does at night. At G3 I told you sleep helps you grow and learn. At G4 I told you about deep sleep and dream sleep. At G5 the Cat is going to organize all of this into three big jobs that sleep does every single night — three jobs that explain why sleep matters so much. Once you know these three jobs, everything else about sleep makes more sense.

The second big idea is how sleep connects with everything else your body does. Just like the Turtle (Coach Brain) showed you in What Your Brain Needs, the Cat is going to show you how sleep connects with every other coach in the Library. The Rooster and I are day-and-night partners. The Bear and I work together on what you eat. The Turtle and I work together on what you learn. The Lion and I work together on movement. We are all one team. Sleep is part of all of it.

The third big idea is the most important, as always. When sleep gets hard. You are old enough now for the Cat to be a little more honest. Sleep can get hard for many reasons at your age — bodies are starting to grow in new ways, friendships are getting more complicated, worries can get bigger. Sometimes sleep changes are a signal that something else is going on. The Cat will help you know what to do.

The Cat purrs slowly. The Cat is patient. Take a slow breath. There is no rush. Begin.

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Lesson 1.1: The Three Big Jobs of Sleep

Learning Objectives

By the end of this lesson, you will be able to:

• Name the three big jobs sleep does at night
• Describe what each job means and why it matters
• Connect deep sleep and dream sleep (from G4) to the three jobs
• Understand that all three jobs happen every single night, in a steady pattern
• Recognize that missing sleep means missing one or more of the three jobs

Key Terms

The Cat Watches

Cats sleep more than almost any other animal. The Cat has been watching what happens during sleep for a long, long time. The Cat is patient about sleep because the Cat is very good at it.

At G3 I told you sleep helps four things — your body, your brain, your mood, and your immune system. At G4 I told you about deep sleep and dream sleep and how they cycle through the night. At G5 the Cat is going to give you a way to organize all of this in your head.

Sleep has three big jobs at night. Three. Just three. Every single night. The Cat's three-job map.

Job 1: BODY-BUILDING. Your body grows, heals, and rebuilds.

Job 2: BRAIN-SAVING. Your brain saves what you learned today and gets ready for tomorrow.

Job 3: FEELING-SETTLING. Your brain sorts through today's feelings so tomorrow can start fresh.

That is sleep, in three jobs. Once you know these, the rest of this chapter makes sense.

Job 1: Body-Building

When you sleep deeply, your body goes to work on itself.

Growing. Your body releases a special chemical — the Cat calls it growing chemistry — that helps your bones grow longer, your muscles grow stronger, and your whole body get bigger. Most of this growing chemistry comes out during deep sleep, especially in the first half of the night [1]. Kids your age are in a growing window. The Cat watches kids your age grow visibly across the year — and most of that growth happens at night, while the kid is sleeping. It is one of the most amazing things about being a kid.

Repairing. Tiny damage from being awake (small muscle tears from movement, sun damage, scrapes, scratches, bumps) gets repaired at night. Your body has special repair systems that work mostly when you are asleep. By morning, most of what was damaged is fixed.

Immune work. Your immune system — the parts of your body that fight off colds, viruses, and infections — does extra work while you sleep. Kids who get good sleep typically get sick less often and recover faster when they do get sick [2]. The Cat has watched this for a long time. It is why grown-ups always tell kids to sleep when they are getting sick — sleep is actually how the immune system gets the time it needs to work.

Hormones and growing chemistry. Many of the chemicals your body makes that control mood, hunger, body temperature, energy, and growth — they all follow daily rhythms tied to sleep. Sleep is when your body resets these chemicals for the next day.

The Cat says: the body does most of its building, healing, and resetting at night. If sleep is short or interrupted, the body has less time to do this work.

Job 2: Brain-Saving

While your body is doing its building work, your brain is doing different work.

The Turtle (Coach Brain) and I are cousin coaches — same as the Dolphin and the Turtle. We work very closely. In What Your Brain Needs, the Turtle taught you about three brain needs: REST, FUEL, USE. Rest is the Cat's domain. The Cat is the brain's rest partner.

Here is what happens during the brain-saving job at night:

Memory sorting. Everything you saw, heard, did, and learned today is sitting in your brain in a temporary place. Your brain has limited space for this temporary stuff. At night, your brain decides what is important enough to save for the long-term and what to let fade. This sorting happens mostly during dream sleep and some during deep sleep [3, 4].

Memory saving. The things your brain decides to save get moved into longer-lasting storage. This is why practicing something during the day and then sleeping makes you better at it. Athletes know this. Musicians know this. Students who have studied for tests know this. Your body and brain do not get better while you practice — they get better during the sleep that follows the practice. The Turtle teaches; the Cat saves.

Connection-building. Your brain physically strengthens the connections between brain cells that you used today, and lets go of connections you did not use. Brain scientists call this pruning — your brain is like a gardener at night, keeping what is useful, letting the rest go [5]. This is one of the most important things that happens during your sleep — and it is happening more during your growing years than at almost any other time in your life. What you do during the day shapes what your brain saves at night. Practice good things. Read good books. Spend time with good people. Try hard things. Your brain saves the patterns.

Getting ready for tomorrow. Your brain also resets for the next day — clearing out chemical waste that built up during the day, refreshing the connections that will run tomorrow, getting ready for new learning. Some scientists call the brain's overnight clean-up system a "wash" — like the brain takes a bath while you sleep [6].

The Cat says: the brain learns at night what was practiced during the day. Without good sleep, much of today's learning is lost.

Job 3: Feeling-Settling

This is the third job, and the one the Cat wants to spend the most time on at G5 because it matters more at your age than at G3 or G4.

During dream sleep, your brain processes today's feelings. It sorts through what you felt. It lets your brain settle from anything that was hard. It readies your feeling system for tomorrow [7, 8].

You can think of it like this: imagine your brain's feeling-room had a busy day. People came in and out. Things got moved around. By the end of the day, the room is a little messy. Dream sleep is when your brain cleans up the feeling-room — puts things back where they go, throws out what is not needed, opens the window to let the air settle. By morning, the feeling-room is mostly cleaned up and ready for a new day.

This is why, when you do not get enough sleep, feelings can feel bigger and harder to handle the next day. Without sleep's cleaning work, the feeling-room is still a mess. Small things feel big. Frustration comes faster. You might feel weepy or grumpy or anxious without knowing why. Many grown-ups who study sleep have found this in research too — kids and teens who do not sleep enough tend to have a harder time with feelings [9].

The Turtle wrote about this in What Your Brain Needs. The Turtle and the Cat are saying the same thing from different sides of the day. Sleep does feeling-settling. Without it, the brain has more trouble managing feelings.

The Cat is gentle here. The Cat is not telling you that bad sleep is the cause of every hard feeling. Feelings are complicated and have many causes. The Cat is just telling you something true: sleep is one of the most powerful ways to support how you feel. If you have been having more big feelings lately, take a look at your sleep first.

The Three Jobs Run All Night

Here is one more thing the Cat wants you to know.

All three jobs happen every single night, in a steady pattern. They are not separate. They overlap. They cycle through the night.

In the first half of the night, your body does more body-building. Deep sleep is longer in the first half. Your growing chemistry releases more in those hours.

In the second half of the night, your brain does more brain-saving and feeling-settling. Dream sleep gets longer toward morning. Your brain spends more time sorting and processing.

That is why sleep timing matters. A kid who goes to bed at 9 PM and wakes at 7 AM gets ten hours — with plenty of body-building in the early hours and plenty of brain-saving and feeling-settling toward morning. A kid who goes to bed at midnight and wakes at 7 AM gets seven hours — and misses the very part of sleep that helps the most with brain-saving and feeling-settling.

Shorter sleep does not just mean less of all jobs equally. It usually means losing the brain-saving and feeling-settling parts more, because those happen later in the night. That is why many kids who stay up late and wake up early feel grouchy, foggy, and emotionally bigger the next day [10].

The Cat has watched this pattern for a very long time. The Cat says: sleep is a gift you give yourself for tomorrow. Going to bed on time is being kind to tomorrow's you.

Lesson Check

1. What are the three big jobs sleep does at night?
2. What is "growing chemistry" and when does most of it release?
3. What happens to today's learning during sleep?
4. What does feeling-settling do? Why does this matter to kids your age?
5. Which jobs happen more in the first half of the night vs the second half?

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Lesson 1.2: How Sleep Connects With Everything Else

Learning Objectives

By the end of this lesson, you will be able to:

• Describe how sleep connects with every other coach's domain
• Explain the Cat-Rooster day-and-night twin partnership
• Describe what you can do during the day to help sleep at night
• Notice that one good night of sleep helps many parts of life the next day
• Understand that sleep is not separate from everything else — it is the night-half of everything you do

Key Terms

The Cat and the Rooster — Day-and-Night Partners

The Cat and the Rooster are the most famous partnership in the Library. We are day-and-night partners.

The Rooster (Coach Light) handles the day half of your body clock. The Cat handles the night half. Same clock. Two halves. We never get to be on duty at the same time — when the Rooster crows at dawn, my shift ends. When the sun sets and the world gets dim, the Rooster goes to roost and my shift begins.

The Rooster told you in How Your Body Uses Light that morning light is the wake-up signal — it locks your body's clock onto "this is when day starts." When that signal is strong (you got outside or near a sunny window in the morning), your body's clock runs smoothly all day. The Rooster's wake-up signal gives the Cat's wind-down signal the timing it needs at night.

A strong morning means an easy bedtime. This is the partnership.

What helps the Cat-Rooster team:

• Open your curtains in the morning, or step outside for a few minutes. The Rooster does the work.
• Keep your wake-up time pretty steady, even on weekends. Big shifts in wake-up time confuse the clock.
• Get outside during the day when you can. Outdoor light is much brighter than indoor and helps your clock stay on track.
• Dim the lights in the evening. Soft warm light is the wind-down signal.
• Turn off bright screens before bed. Screens look like daylight to your clock cells (the Rooster told you).
• Sleep in a dark room. Curtains closed. Big lights off.
• Bed = sleep. Not bed = scrolling, bed = TV, bed = homework. Beds are for sleeping and sometimes reading paper books. Your body learns "in bed, I sleep."

The Cat and the Rooster have been saying this since G3. We will keep saying it because it works. Your body clock is your most important sleep tool. Take care of it and sleep gets easier.

The Cat and the Bear — Fuel and Sleep

The Bear (Coach Food) and I have a partnership too. The Bear taught you in What Food Is Made Of that food is what your body uses to grow and repair. Sleep is when most of that growing and repairing happens.

That means: what you eat during the day affects sleep at night, and sleep at night affects what your body does with food the next day.

The Bear and the Cat rules together:

• Eat real food across the day. Skipping meals can make sleep harder.
• Eat your last big meal a couple of hours before bed. Not right before. Your tummy works hard on a big meal, and tummy work makes sleep harder.
• A small light snack before bed is okay if you are hungry — a piece of fruit, a few crackers with peanut butter, a small bowl of yogurt. Going to bed hungry makes sleep harder too.
• Skip caffeine. Caffeine is in coffee, many sodas, energy drinks, some teas, and chocolate. Caffeine keeps the brain busy when it should be settling. Kids your age generally do best skipping caffeine, especially after lunchtime [11]. The Cat is firm about this one.
• Skip big sugar close to bedtime. A big sugary snack right before bed can give a burst of energy when your body wants to wind down.
• Stay hydrated during the day so you do not have to drink a lot right before bed (otherwise you may wake up in the middle of the night needing the bathroom). The Elephant said this too.

The Cat and the Bear: real food, regular meals, light evenings.

The Cat and the Turtle — Cousin Coaches

The Turtle (Coach Brain) is the Cat's cousin coach. We work very closely.

The Turtle taught you in What Your Brain Needs that the brain has three needs: rest, fuel, use. Rest is mine. The Cat is the brain's rest partner.

Everything you learned today gets saved while you sleep (Job 2, brain-saving, from Lesson 1). Everything you felt today gets processed while you sleep (Job 3, feeling-settling). The Cat does this work for the Turtle's brain every night.

What this means in real life:

• Study or practice in the day; let sleep save it. Studying through the night does not help. Sleep is when the saving happens.
• A short rest after intense learning helps too. Even a quiet break (no screens) lets the brain pause.
• If you are working on something hard, sleep on it. Many kids and grown-ups solve problems overnight without trying. The brain keeps working while you rest.
• Hard feelings about brain stuff (school, friends, big worries) usually feel a little smaller after a night of sleep. Not always. But often.

The Cat and the Turtle: practice during the day, save and settle at night.

The Cat and the Lion — Daytime Movement Helps Sleep

The Lion (Coach Move) and I have a partnership most kids do not know about.

Kids who move their bodies during the day usually sleep better at night [12]. This is one of the most reliable findings in pediatric sleep research. Running around, playing sports, dancing, biking, hiking, climbing — all of these tire your muscles in good ways and signal to your body that it has done its day's work. Bodies that have moved during the day are more ready to rest at night.

The Cat and the Lion rules:

• Move every day. Even small amounts help. Recess, walking to school, playing outside, dance, sports — anything that gets you moving and breathing.
• Move earlier in the day if you can. Hard exercise right before bed (within an hour) can be too stimulating for some kids. A gentle walk after dinner is fine. A high-intensity game right before bedtime might not be.
• Outdoor movement is extra good because it combines the Lion's job with the Rooster's job — sunlight on the body clock plus the body using itself.

The Cat and the Lion: move during the day, sleep at night.

The Cat and the Dolphin — Breath and Sleep

The Dolphin (Coach Breath) and I work together too.

You breathe while you sleep — about ten to twenty thousand times a night. Your breath gets slow, steady, deep. This automatic-mode breathing is what your body wants during sleep.

Slow breath also helps fall asleep. When kids have trouble settling at bedtime, the Dolphin's simple slow-breath practice (a few slow breaths, with the out-breath a little longer than the in-breath) can help the body shift toward sleep. The Cat and the Dolphin both like this.

If breath problems wake you up at night, like coughing that won't stop, wheezing, asthma flare-ups, or trouble breathing comfortably — tell a trusted grown-up. Night breathing problems are something doctors want to know about.

The Cat and the Dolphin: easy breath, easy sleep.

The Cat and the Elephant — Water Balance

The Elephant (Coach Water) and I have a small but real partnership.

Stay hydrated during the day so your body has water to do its overnight work. All three of the Cat's three jobs need water — body-building uses water, brain-saving uses water, feeling-settling uses water. But:

Do not drink huge amounts of water right before bed, or you will be waking up to use the bathroom in the middle of the night, which interrupts sleep cycles.

The Cat and the Elephant: water through the day, less in the last hour before bed.

The Cat and the Penguin / Camel — Sleeping Temperature

The Penguin (Coach Cold) and the Camel (Coach Hot) both work with the Cat on bedroom temperature.

A slightly cool sleeping room helps most kids sleep better [13]. Your body's core temperature actually drops a bit when you fall asleep — and a cool room makes that drop easier.

• Too hot: sleep is restless, harder to fall into, sweaty, broken.
• Too cold: kids may wake up uncomfortable.
• Cool and comfortable (with appropriate blankets and pajamas): the sweet spot.

The Penguin and the Camel both said this in their G4 chapters. The Cat says it again. Trusted grown-ups in your family set the bedroom temperature.

The Whole Team Through Sleep

Sleep is connected to every coach. Whatever a coach does during the day shows up in sleep at night, and whatever the Cat does at night shows up the next day in every coach's domain.

Bear good fuel → better growing at night → more energy tomorrow. Lion good movement → better sleep → better Lion the next day. Turtle good learning → saved at night → smarter tomorrow. Dolphin calm breath → easier sleep → calmer breath tomorrow. Elephant good hydration → smoother sleep → less foggy tomorrow. Rooster good morning light → smoother body clock → sleepy at the right time tonight. Penguin/Camel right temperature → comfortable sleep all night.

Sleep is the night-half of everything you do. That is the G5 Connect lesson for the Cat. The Cat thinks about this often.

Practice With a Trusted Grown-Up

The Cat has a small thing for you to try.

Find a trusted grown-up. Ask them: "Can we look at my sleep this week and see what is going well and what we could try?"

Together, talk about:

• Bedtime. What time do I usually go to bed? Same time most nights? Or different?
• Wake-up time. What time do I usually wake up? Same on weekends or different?
• Wind-down. What does the last hour before bed usually look like? Screens? Reading? Talking? Activity?
• Sleep room. Is my room dark enough? Cool enough? Comfortable?
• What is one thing we could try this week? Pick ONE small change. Just one.

Some ideas:

• Steady bedtime, even on weekends (within 30 minutes)
• Phones / tablets out of the bedroom at bedtime
• Dim the lights an hour before bed
• A short reading time with a paper book before sleep
• Curtains closed for full darkness
• Cooler bedroom temperature
• An outdoor break in the morning before school

The Cat is patient. Small changes over many weeks build good sleep. The Cat is proud of you for paying attention.

Lesson Check

1. Describe the Cat-Rooster day-and-night twin partnership.
2. What are three Cat-and-Bear rules about food and sleep?
3. What does the Turtle-Cat cousin partnership do for your learning?
4. Why does the Lion (movement) help the Cat (sleep)?
5. Why is a slightly cool bedroom better than a warm one for most kids?

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Lesson 1.3: When Sleep Gets Hard

Learning Objectives

By the end of this lesson, you will be able to:

• Describe normal sleep changes for kids your age (10-11)
• Recognize patterns that mean sleep needs a trusted grown-up's help
• Understand that sleep difficulty and big feelings often happen together
• Know basic sleep-safety rules (sharing a room safely, screens at night, never sleep-deprive on purpose)
• Repeat the crisis resources for hard feelings, knowing that some sleep changes signal mental-health help

Key Terms

The Cat Is Honest

The Cat has been gentle so far. The Cat has been patient. The Cat has shown you what sleep does, how it connects with everything, and what helps.

Now the Cat has to be honest, because you are old enough to know.

Sleep can change at your age. Some of those changes are normal and developmental. Some of those changes are signs that something else is going on. The Cat is going to teach you the difference.

Normal Sleep Changes for Kids Your Age

Body-clock shifting later. As kids grow toward the teen years, their body clocks naturally shift a little. The sleep window — the hours when the body wants to sleep — slowly moves later [14]. A nine-year-old who could fall asleep at 8:30 PM easily might, at age 10 or 11, find their body not getting sleepy until 9:30 or even later. This is real. It is biology. Bodies change.

This does not mean you should stay up later. Most kids your age still need a lot of sleep (the Turtle said about 9-11 hours; the Cat agrees). It means you may need to work a little harder at your wind-down so you can still get the sleep you need. It also means morning light is more important than ever — the Rooster's morning signal helps push the clock earlier when biology is pushing it later.

Bodies starting to grow in new ways. Many kids your age are starting puberty — the changes that turn kid bodies into teen bodies into adult bodies. (Some kids start at 9 or 10. Some at 12 or 13. Different kids start at different times — that is all normal.) Puberty changes a lot of things, including sleep. Some kids in early puberty need more sleep than they did before. Some kids find their sleep gets more disrupted. This is normal. The Cat is not going to teach you all about puberty here — that is your trusted grown-ups' and your school's job. The Cat just wants you to know that sleep changes during puberty are real, normal, and worth talking about with a trusted grown-up.

Dreams getting more complex. Many kids your age start having more vivid, more complicated, sometimes weirder dreams. Sometimes good dreams. Sometimes confusing ones. Sometimes nightmares. This is normal. The brain is doing more sophisticated sorting work as it grows. If nightmares are frequent and disturbing, tell a trusted grown-up — but the occasional bad dream is part of having a working brain.

Friend stuff keeping you up. As kids grow, social life gets more complicated. Things friends said, things that happened at school, worries about the next day — all can show up at bedtime when the room gets quiet and the day's busyness fades. This is normal too. Slow breath (the Dolphin's), telling a trusted grown-up before bed, writing in a journal — any of these can help. If thinking-too-much-at-bedtime gets stuck and stays stuck, tell a grown-up.

When Sleep Gets Hard in a Worrying Way

The Cat now gives you the patterns to watch for. These are sleep changes that mean tell a trusted grown-up:

• Trouble falling asleep for many nights in a row (more than a week or so), even when you are tired.
• Waking up many times during the night and not falling back to sleep easily.
• Waking up too early and not being able to get back to sleep.
• Feeling exhausted all day even though you spent enough time in bed.
• Bad dreams or nightmares every night for more than a few weeks.
• Snoring loudly, gasping, or stopping breathing in your sleep (often reported by parents or siblings who hear it). This is something doctors will want to know about.
• Walking, talking, or doing things in your sleep — not just once but as a regular pattern.
• Sleep getting worse during a hard time (after a loss, a move, family changes, school stress) and not getting better after a couple of weeks.
• Feeling really sad, anxious, or stuck along with the bad sleep. Sleep and feelings travel together; both might need help.
• Wanting to stay up to avoid sleeping because something about sleep itself is scary or because of nightmares.

Any of these — tell a trusted grown-up. Most of these have help. Doctors and counselors who work with kids know all of these patterns and can help.

The grown-up may:

• Sit and talk with you about what is going on
• Adjust the bedtime routine, the bedroom, or the wind-down
• Take you to a pediatrician to check that nothing physical is happening
• Take you to a counselor or therapist if sleep is connected to harder feelings
• Sometimes, in some cases, a doctor may recommend specific help

The Cat says: sleep difficulty is one of the easiest things in the world to fix when you ask for help, and one of the hardest when you do not. Tell a grown-up early. Not later.

Sleep and Big Feelings — The Same Conversation

The Turtle taught you in What Your Brain Needs that some feelings get bigger at your age. The Cat has to tell you that sleep changes are often part of that picture.

When kids your age start having stuck-feelings — anxiety that won't quiet, sadness that won't lift — sleep usually changes too. Either sleeping less (mind racing, worry at night, can't fall asleep) or sleeping more (wanting to hide under blankets all the time, hard to get up, tired all day even after long sleep).

If your sleep has changed and your feelings have changed, both of them are talking. Listen. Tell a trusted grown-up.

The Turtle and the Cat are on the same team here. We are saying the same thing from different sides. Sleep and feelings are connected. The same trusted-grown-up rule applies. The same crisis resources apply. The same "asking for help is brave" message applies.

The Cat is patient. The Cat is not going to scare you. The Cat is going to tell you the truth: a lot of kids your age have nights or weeks of hard sleep. Most of them get better with help. You can be one of them.

Sleep Safety

A few sleep-safety notes the Cat wants to make sure you know:

Never try to stay awake all night on purpose. Some kids dare each other to "pull an all-nighter" or stay up to see how long they can. The Cat says no. Sleep deprivation hurts your body, your brain, and your mood — even just one night can affect you for days. Older grown-ups doing this (for work, for emergencies) is one thing. Kids doing this for fun is not safe.

No screens in bed. The Rooster, the Cat, and every pediatric sleep guideline agree — screens belong out of the bedroom at bedtime. If you have a phone, it should charge in the kitchen or living room at night, not next to your pillow.

Sharing a room safely. If you share a room with siblings or family, sleep-safety still matters — your sleep schedule, your wind-down, your quiet time matters. Talk with your trusted grown-ups about how to make a shared room work for everyone's sleep.

Tell a grown-up about scary stuff. If something is scary at night (a creak, a bad dream, a worry, a sound you cannot explain), it is okay to tell a trusted grown-up. They will help. Kids your age sometimes feel they should not need help with this anymore. The Cat says: every age needs help sometimes. Especially with sleep.

Sleepovers and traveling. Sleeping in new places can disrupt sleep. That is normal. A favorite stuffed animal or pillow can help. So can the same wind-down routine. So can a flashlight if it is darker than you are used to. Tell the grown-ups taking care of you (a friend's parent at a sleepover, a relative on a trip) about anything you need.

Feelings About Sleep

Some feelings about sleep you might have:

• Worried about not falling asleep (the worry can keep you awake — circular, normal)
• Scared of nightmares
• Frustrated about how hard sleep has been lately
• Anxious about going to bed
• Embarrassed about needing a stuffed animal or a night-light at your age (no shame; many kids and adults sleep better with familiar comfort items)
• Sad about having to go to bed when you would rather stay up
• Sleepy in a normal way (the Cat loves this one)

All of these are normal. If a feeling about sleep is sticking around or making sleep harder, tell a trusted grown-up. Same trusted grown-ups. Same rules. Same team.

You can start small:

• "I have been having trouble falling asleep this week."
• "I keep having bad dreams."
• "My brain won't stop thinking at bedtime."
• "I feel tired all the time even though I sleep a lot."
• "I'm scared of something but I don't want to say what."

Any of those is a great start.

Crisis Resources

These are the helpers grown-ups can use when feelings (including feelings about sleep, the body, or anything else) get really big or unsafe. Same as the Turtle's chapter. The Cat repeats them because every coach should.

For an emergency where someone needs help right away:

• A grown-up can call 911. Real people answer fast and send help.

For feelings that feel really scary or unsafe — including thoughts of hurting yourself or not wanting to be here:

• The 988 Suicide and Crisis Lifeline. A grown-up (or you, if you have been taught) can call or text 988, day or night. Real people answer. They help right away.
• The Crisis Text Line. A grown-up can text the word HOME to 741741, day or night.

For other big or hard worries:

• The SAMHSA National Helpline at 1-800-662-4357. Day or night.

For grown-ups concerned about a kid's eating, body image, or food:

• The National Alliance for Eating Disorders at 866-662-1235, weekdays 9 to 7 Eastern.

Same numbers across every coach's chapter. Same team. You are never alone with sleep, with feelings, with anything.

The Cat's Last Thought

Before we end this chapter, the Cat wants to give you one last thought.

Sleep is one of the kindest things you can do for yourself.

Every night, you give your body time to grow and heal. You give your brain time to save what you learned and to settle what you felt. You give your whole self a fresh start for tomorrow. Sleep is a gift you give yourself, every single night, just by lying down and letting it happen.

The Cat does this for hundreds of years (well, the Cat has been around a long time). The Cat watches kids learn this slowly. Some kids fight sleep when they are young — they do not want to miss anything. They want to stay up. They want one more chapter, one more game, one more episode. The Cat understands. The Cat is patient.

But the Cat also knows: the kids who learn to love sleep grow up well. Their bodies grow. Their brains save what they learned. Their feelings settle. They wake up ready for whatever tomorrow brings. Sleep does not stop life — sleep makes life work.

The Cat curls up beside you. The Cat's eyes are half-closed. The Cat is purring softly. Take a slow breath. Sleep is your friend. The Cat will see you tomorrow.

Lesson Check

1. What is a normal sleep change for kids your age that the Cat called "body-clock shifting later"?
2. Name five patterns that mean sleep difficulty needs a trusted grown-up's help.
3. Why are sleep and feelings often a "same conversation"?
4. Why does the Cat say "never try to stay awake all night on purpose"?
5. What is 988, and what is the rule about kids using it?

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End-of-Chapter Activity: A Sleep-Noticing Week

The Cat has a noticing project for you. It runs for seven days, with a trusted grown-up checking in. Like the G5 Food and G5 Brain projects, this is meant to build awareness, not perfection.

What you need

• A small notebook or piece of paper
• A pencil
• A regular bedtime to keep
• A trusted grown-up checking in each day

What to do

Each day for seven days, you will write down three short notes about your sleep.

1. What time I went to bed. (One sentence.)

2. What time I woke up. (One sentence.)

3. How rested I felt during the day, on a 1-10 scale. (One sentence.)

Optional fourth note: One thing about my wind-down last night. What was the last hour before bed like? Screens? Reading? Activity? Talking?

That is the whole project. Three or four short notes a day. Seven days.

After seven days

Look at your twenty-one or twenty-eight notes. What do you notice?

• Which nights did you sleep the most? What was different about those days?
• Which nights did you sleep the least? What was different?
• Did the 1-10 rested-feeling scores match the hours-slept, or were some surprising?
• What kind of wind-down felt best?

Talk with your trusted grown-up. Pick one sleep habit to try for the next two weeks. Just one. Some ideas:

• Steady bedtime, even on weekends (within 30 minutes)
• Phones out of the bedroom at bedtime
• Dim the lights an hour before bed
• A reading-in-bed routine with a paper book
• Curtains closed for full darkness
• Cooler bedroom temperature
• An outdoor morning break before school

The Cat is patient. Small habits over many weeks build great sleepers.

Optional extra

If you and your family keep the sleep-noticing notebook going for a whole month, the Cat will be very happy. The Cat is proud of any family that takes sleep seriously.

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Vocabulary Review

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Chapter Review

1. What are the three big jobs of sleep at night?
2. What is "growing chemistry," and when does most of it release?
3. How does sleep help with learning? (Hint: the Turtle's partnership.)
4. What does feeling-settling do? Why is this connection important at your age?
5. Why does the Cat say going to bed earlier helps more than just "more total hours"?
6. Describe the Cat-Rooster day-and-night partnership.
7. Name three Bear-and-Cat rules about food and sleep.
8. Why does daytime movement (the Lion) help nighttime sleep (the Cat)?
9. Why is a slightly cool sleeping room better than a warm one?
10. What is the "body-clock shift later" that happens at your age?
11. Name five patterns that mean sleep difficulty needs a trusted grown-up's help.
12. Why are sleep and feelings often the "same conversation"?
13. Why does the Cat say "never stay awake all night on purpose"?
14. What is the Cat's last thought about sleep?

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Instructor's Guide

Pacing recommendations

This G5 Sleep chapter is the THIRD chapter of the G5 cycle and the third chapter in the Cat's K-12 spiral. Three lessons span eight to ten class periods. The seven-day sleep-noticing activity adds out-of-class time with family check-ins.

• Lesson 1.1 (The Three Big Jobs of Sleep): three class periods. The three-jobs framing (body-building / brain-saving / feeling-settling) is the G5 structural deepening that parallels G5 Food's three-parts and G5 Brain's three-needs. The first-half-of-night vs second-half-of-night content (which jobs run when) is new at G5.
• Lesson 1.2 (How Sleep Connects With Everything Else): three class periods. The most Connect-themed lesson in the chapter; reinforces the Cat-Rooster day-and-night twin partnership from G4 Light; explicitly names every other coach's relationship with sleep.
• Lesson 1.3 (When Sleep Gets Hard): two to three class periods. The pre-adolescent body-clock-shift content is new at G5. Puberty briefly mentioned at age-appropriate framing only (the chapter explicitly does not teach puberty content). Mental-health-and-sleep cross-walk with G5 Brain Lesson 3. Coordinate with school counselor and families before teaching.

Lesson check answers

Lesson 1.1

1. Body-building (growing, healing, immune work), Brain-saving (memory consolidation, learning saved), Feeling-settling (mood reset, emotional processing).
2. Growing chemistry is the chemical that helps the body grow. Most of it releases during deep sleep, especially in the first half of the night.
3. The brain decides what to save and what to let go. Practice during the day + sleep at night = learning that sticks.
4. Feeling-settling cleans up the brain's "feeling-room" so the next day starts fresh. Without it, feelings can feel bigger and harder to handle. Important at age 10-11 because mental health vigilance is heightened.
5. Body-building (deep sleep) happens more in the first half. Brain-saving and feeling-settling (dream sleep) happen more in the second half.

Lesson 1.2

1. Same body clock, two halves. Rooster handles day; Cat handles night. Morning light helps set the clock, which makes evening sleep happen on time.
2. Sample: real food across the day, don't skip meals, last big meal a couple hours before bed, light snack OK if hungry, skip caffeine, skip big sugar close to bedtime, hydrate during the day not right before bed.
3. The Turtle's brain learns during the day; the Cat saves what was learned at night. Practice plus sleep equals learning that sticks.
4. Moving during the day tires muscles in good ways and signals to the body that day-work is done. Bodies that have moved are more ready to rest.
5. The body's core temperature drops a little during sleep. A cool room makes that drop easier; a hot room makes sleep restless.

Lesson 1.3

1. The natural shift in sleep timing as kids grow toward teen years — body clocks want to start sleep later. Pronounced in teens; beginning in some 10-11 year olds.
2. Sample five: trouble falling asleep for many nights, waking many times, waking too early, feeling exhausted all day, frequent nightmares, snoring/gasping/breathing stops in sleep, sleepwalking/talking pattern, sleep getting worse during hard times, big feelings along with bad sleep, avoiding sleep due to nightmares.
3. When sleep changes, feelings usually change too — and vice versa. Sleep and feelings travel together at the body-brain level. Both might need help; same trusted grown-up framing.
4. Sleep deprivation hurts body, brain, and mood — even one night affects you for days. Kids doing this for fun is not safe.
5. 988 is the Suicide and Crisis Lifeline. Kids your age usually tell a grown-up first; older kids may call directly with grown-up guidance in crisis.

Chapter review answer key

1. Body-building, Brain-saving, Feeling-settling.
2. Growing chemistry helps you grow. Most releases during deep sleep, especially in the first half of the night.
3. Learning saved at night during brain-saving. Sleep is when the brain decides what's important and moves it to longer storage. Turtle teaches; Cat saves.
4. Feeling-settling cleans up the brain's emotional state from the day. Important for kids age 10-11 because feelings are getting bigger and need more processing.
5. Brain-saving and feeling-settling run more in the second half of the night. Late bedtime + early wake time = losing the brain-and-feeling work specifically, not just hours.
6. Same body clock; Rooster handles day, Cat handles night. Morning light sets the timing for evening sleep.
7. Sample: eat across day; last big meal a couple hours before bed; light snack OK if hungry; skip caffeine; skip big sugar at bedtime; hydrate earlier not just before bed.
8. Daytime movement tires muscles in good ways, signals day-work-done, helps the body fall asleep more easily and sleep more deeply.
9. Body core temperature drops a little during sleep; cool room makes the drop easier.
10. Sleep window shifts later as kids grow toward teen years. Bodies don't get sleepy at the same time they used to.
11. From the chapter: trouble falling asleep for many nights, waking many times, waking too early, exhausted all day, frequent nightmares, snoring/gasping, sleepwalking pattern, sleep worse during hard times, sleep + big feelings together, avoiding sleep.
12. Sleep changes and feeling changes usually happen together at this age. Both signal that something needs attention.
13. Pulling all-nighters hurts body, brain, mood. Even one night of zero sleep can affect you for days. Not safe for kids.
14. Sleep is one of the kindest things you can do for yourself. A gift you give yourself every night. The kids who learn to love sleep grow up well.

Discussion prompts

1. What was new in this chapter that you did not know before?
2. The Cat says sleep has three big jobs. Which one feels most important to you and why?
3. Have you noticed your body wanting to sleep at a different time than it used to? (Held sensitively. This is the body-clock-shift question.)
4. The Cat-Rooster day-and-night partnership is one of the most famous in the Library. What other coach pairs have a special relationship? (Bear-Lion, Bear-Elephant, Turtle-Dolphin, Penguin-Camel, etc.)
5. If a friend told you they were sleeping badly for weeks, what would you say or do?
6. Why does the Cat say "asking for help with sleep is easy and helps fast"?
7. What is one sleep habit you would like to try?
8. Why is sleep called "a gift you give yourself"?

Common student questions

1. "How much sleep do I actually need?" — Most kids ages 10-11 need about 9-11 hours a night. Some kids do better with a little less, some with a little more. Listen to how rested you feel during the day. If you are tired all morning, you probably need more.
2. "What if I cannot fall asleep?" — Some nights are like that. Slow breath, a paper book, a calm thought, dim light. If it happens for many nights in a row, tell a trusted grown-up.
3. "What about napping?" — Naps can be helpful — short ones (20-30 minutes) early in the afternoon are usually fine for kids your age. Long late naps can make nighttime sleep harder. Some kids need naps when they are growing or sick; others do not nap from age 5 onward. Different.
4. "What is sleep paralysis?" — A name for an experience where you wake up but cannot move for a few seconds. Happens to some people. Usually harmless. If it happens often or scares you, tell a trusted grown-up.
5. "What about Andrew Huberman / sleep optimization / sleep protocols?" — A lot of adult sleep content online is made for grown-ups. Specific protocols are not appropriate prescriptions for kids your age. The Cat teaches what works for kids — steady bedtime, good wind-down, cool dark bedroom, daytime light and movement, real food earlier. That is enough.
6. "What about melatonin pills?" — Melatonin is a chemical your body makes naturally. Some grown-ups take it as a pill. For kids, a doctor decides if it fits a specific situation. The Cat does not recommend kids your age take melatonin without a doctor's guidance. Many kids who think they need it actually need better wind-down and a steadier bedtime instead.
7. "What about sleepovers and travel?" — Different beds, different rooms, different noises — sleep can get disrupted. That is normal. A favorite item, the same wind-down routine, and telling the grown-ups what you need all help.
8. "What if I share a room with siblings and they keep me up?" — Talk with a trusted grown-up about how to make a shared room work. Earplugs (with permission), a sleep mask, agreed-upon quiet times, different bedtimes — all can help.

Parent communication template

Dear families,

This week we are reading Chapter 1 of the Grade 5 Coach Sleep (Cat) chapter — What Sleep Does. This is the third chapter in the Cat's spiral (G3 was Your Sleep and You, G4 was How Sleep Works) and the third chapter in the Grade 5 Library cycle.

The chapter teaches three big ideas: what sleep does at night (three big jobs — body-building, brain-saving, feeling-settling; deep sleep and dream sleep from G4 connected to the three jobs; the first-half vs second-half pattern that explains why bedtime timing matters); how sleep connects with every other coach's domain (Cat-Rooster day-and-night twin; Cat-Bear food rules; Cat-Turtle brain-saving; Cat-Lion daytime movement; Cat-Dolphin breath; Cat-Elephant hydration; Cat-Penguin/Camel temperature); and when sleep gets hard (normal developmental shifts at age 10-11, patterns that mean tell a trusted grown-up, the sleep-and-feelings connection, crisis resources, sleep safety).

Important developmental content at G5: the chapter explicitly normalizes that body clocks naturally shift later as kids approach teen years, and briefly acknowledges that puberty (which begins for some kids at age 9-10) affects sleep. The chapter does NOT teach puberty content — that is your family's and school's role. The chapter simply names that bodies-are-starting-to-grow-in-new-ways is real and that sleep changes during this window are normal.

Mental-health-and-sleep: the chapter makes the sleep-and-feelings connection explicit at G5 framing (without naming clinical diagnoses). The sleep-changes-as-signal-of-emerging-anxiety/depression pattern is named. The Turtle-Cat partnership in Lesson 3 mirrors and reinforces the mental-health-vigilance content in the just-shipped G5 Brain chapter (What Your Brain Needs). Crisis resources (988, Crisis Text Line, SAMHSA, National Alliance for Eating Disorders, 911) are listed at age-appropriate framing.

The end-of-chapter activity is a seven-day sleep-noticing project — kids will track bedtime, wake-up time, and a 1-10 rested-feeling score for seven days, with a family check-in. At the end of the week, your child will discuss with you and pick one family sleep habit to try.

If at any point your child shares something concerning — about sleep, feelings, friendships, body changes — please reach out. We are a team.

Thank you for being part of your child's learning.

Anticipated parent concerns and responses

• "Why mention puberty at all in a fifth-grade chapter?" Puberty begins for many kids between ages 9 and 13, and most kids start to notice some changes by age 10-11. Naming that bodies-are-starting-to-grow-in-new-ways at age-appropriate framing is consistent with pediatric guidance and prepares kids to expect normal sleep changes. The chapter does not teach puberty content; that role belongs to families, doctors, and the school's age-appropriate health curriculum.
• "What about the body-clock-shift later content? Doesn't that just tell kids to stay up late?" No — the chapter explicitly says most kids still need 9-11 hours and that morning light is more important than ever to counter the natural shift. The framing is "biology is shifting; here's how to keep good sleep anyway."
• "My child has insomnia or another sleep condition. Is the chapter okay for them?" Yes — the chapter normalizes sleep difficulty as common, names insomnia as a real condition with help, and explicitly routes to doctors and counselors. If your child sees a sleep specialist, the chapter aligns with most pediatric sleep guidance.
• "Are video games / screens really that bad for sleep?" Bright screens close to bedtime affect the body clock's wind-down signal and can keep the brain stimulated when it should be settling. Pediatric guidance (AAP, AASM) supports screens out of the bedroom at bedtime for this age. The chapter does not prescribe specific hours; family choice with pediatric input.
• "What about melatonin?" The chapter teaches that doctors decide if melatonin fits a specific kid. The Cat does not recommend it without a doctor's guidance. Many kids who think they need it actually need a better wind-down and steady bedtime.
• "My child is afraid to sleep alone. Is that normal at 10-11?" Some kids are. Sleep fears can come and go. Talk with a trusted grown-up; if it is sticking, a pediatrician or counselor can help. The Cat normalizes this gently in Lesson 3.

Founder review notes — safety-critical content protocol

This chapter is flagged founder_review_required: true because it covers multiple safety-critical content categories:

• Mental health vigilance (load-bearing). Lesson 3 makes the sleep-and-feelings connection explicit at G5 framing. The sleep-changes-as-signal pattern is named. Anxiety and depression patterns acknowledged. Self-harm and crisis-resource section preserved from G5 Brain framing. Citations 7, 8, 9 anchor sleep-and-mood research.
• Pre-adolescent vulnerability. Body-clock shift acknowledged. Puberty briefly mentioned. Mental-health-and-sleep cross-walk with G5 Brain. The chapter explicitly does NOT teach puberty content or sexual content — that boundary held throughout.
• Sleep safety. No-all-nighters rule load-bearing. Screens out of bedroom. Safe room-sharing. Telling-grown-ups-about-scary-things rule. Sleepover and traveling safety briefly mentioned.
• Age-appropriate health messaging. No REM/NREM technical naming (G6+ territory). No melatonin / adenosine / SCN / cortisol technical naming (G6+); body-clock and growing-chemistry framing only. No clinical sleep disorder naming (only insomnia as a vocabulary word, framed as "real, common, has help"). No prescriptive intervention schedules.
• Body-positive vigilance. Sleep needs vary by kid framing throughout. No comparison framing. Body changes-during-puberty normalized.
• Medical claims. All descriptive framing. No prescriptive health claims. Melatonin pills framed as doctor-decided. Sleep medications NOT taught at this grade.
• Crisis resources. Re-verify all phone numbers and URL currency at publication: 911, 988 Suicide & Crisis Lifeline, Crisis Text Line (HOME to 741741), SAMHSA 1-800-662-4357, National Alliance for Eating Disorders 866-662-1235. NEDA helpline 1-800-931-2237 is non-functional as of this writing and is not cited.

Influence-zone discipline

K-12 influence-free zone is total exclusion — Saladino, Brecka, Hamilton, Greenfield, Huberman, Hof are absent from body content at every K-12 grade. Sleep is a notable Huberman popular-culture domain alongside neuroscience; the chapter teaches sleep function and sleep optimization thoroughly using foundational research (Tononi & Cirelli, Paruthi, Carskadon, Walker, Goldstein-Walker, Gradisar) without naming any contemporary popularizer. The anticipated parent/student question about "Andrew Huberman / sleep optimization / sleep protocols" is addressed in Common Student Questions with the standard "adult content; not appropriate for kids your age; what the Cat teaches is enough" response.

Cycle position notes

This chapter is the THIRD chapter of the G5 cycle. The Bear opens (G5 Food); the Elephant lands (G5 Water). The Cat's G5 chapter deepens the Connect theme by showing how sleep is the night-half of every coach's domain — pairing structurally with the Turtle's G5 chapter which positioned the brain as the integration point of every coach's domain. Together, G5 Brain and G5 Sleep form the most Connect-themed pair of the G5 cycle so far.

What this chapter does not teach

REM/NREM technical naming (G6+ territory; preserved deep-sleep and dream-sleep from G4 as G5 vocabulary), melatonin / adenosine / SCN / cortisol naming in body content (G6+; body-clock and growing-chemistry framing only), clinical sleep disorders by name beyond the single insomnia vocabulary word framed gently (G6+), puberty content beyond the briefest "bodies are growing in new ways" acknowledgment (family and school territory), sexual content of any kind (not in K-12 Library), specific sleep medication protocols, hypnogram math, exact cycle math beyond G4's "~90 minutes mentioned," or any branded sleep protocol or contemporary popularizer.

Lesson 1.3 special note

Lesson 1.3 carries the chapter's most load-bearing safety material — the sleep-and-mental-health connection. The patterns-to-tell-grown-ups list calibrated for age 10-11; the sleep-and-feelings same-conversation framing reinforces G5 Brain Lesson 3; crisis resources prominently featured; sleep-deprivation-is-not-safe framing explicit. The puberty mention is brief, age-appropriate, and clearly delegated to family and school for detailed teaching.

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Illustration Briefs

Lesson 1.1

• The three jobs of sleep diagram. A clear, friendly illustration of a child peacefully asleep at night with three labeled arrows pointing into them: BODY-BUILDING (icons of bones, muscles, immune-shield), BRAIN-SAVING (icons of file folders, memory symbols), FEELING-SETTLING (heart with sorting arrows, soft glow). The Cat curled at the child's feet, purring. Show diverse skin tones and family compositions.
• First-half / second-half timeline. A simple horizontal timeline showing one night of sleep with two zones: "First half — more body-building" (with body and bone icons) and "Second half — more brain-saving + feeling-settling" (with brain and feeling icons). A clock at each end showing 10 PM and 7 AM. The Cat sleeping nearby.
• The dream-sleep feeling-room. A whimsical illustration of a brain's "feeling room" — a small cozy room with shelves of feelings being sorted and put away. Dream-sleep is happening (small dream cloud above). Mood: gentle, never scary, never anatomical.

Lesson 1.2

• Day-and-night clock. A circular 24-hour clock showing day-side (with the Rooster on a fence and the sun) and night-side (with the Cat curled up and the moon). At sunrise and sunset, the two coaches gently touch wing-to-paw. Caption: "Same clock. Two halves."
• Whole-team-at-night. A circular diagram showing a sleeping child at center with arrows from each of the other coaches pointing inward (Bear, Turtle, Lion, Penguin, Camel, Dolphin, Rooster, Elephant) — each arrow labeled with what that coach gives sleep. The Cat curled at the child's feet. Mood: connected, peaceful.
• Wind-down evening. A scene of a family in soft warm evening light: dim lamps, a kid reading a paper book in pajamas, no screens, water glass on a bedside table, curtains starting to close. The Cat sitting on the edge of the bed. Mood: ordinary, doable, calming.

Lesson 1.3

• Sleep-window shifting. Two age-comparison panels. Left: a 9-year-old falling asleep easily at 8:30 PM. Right: the same child at 10-11, still awake at 9:30 PM, looking surprised but okay. Caption: "Bodies grow. Sleep windows shift. The Cat understands." Mood: gentle, matter-of-fact, never alarming.
• Sleep-and-feelings tied together. A simple illustration of two figures (sleep on one side, feelings on the other) connected by a soft line, with arrows showing they affect each other. The Cat in the middle, smiling gently. Caption: "When sleep changes, feelings often do too. Both deserve attention."
• Asking for help with sleep. A scene of a kid talking to a trusted grown-up about sleep — maybe at the breakfast table, both calm, the grown-up listening attentively. The Cat in the background, looking warm. Caption: "Telling a grown-up about hard sleep is easy and helps fast."
• The Cat's last thought. A peaceful closing illustration of the same child curled up asleep, the Cat curled beside them, the room dim. Outside the window, stars and a soft moon. The Rooster faintly visible in the distance, getting ready for sunrise but not yet active. Mood: peaceful, hopeful, "sleep is your friend."

Aspect ratios: 16:9 for web display, 4:3 for print conversion. All illustrations show diverse skin tones, body types, hair textures, gender expressions, sleeping arrangements (some kids share rooms, some have their own; some have bunk beds; some are in family beds appropriately framed). The Cat's character design carries forward from G3 and G4 Sleep.

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Citations

1. Van Cauter E, Plat L. (1996). Physiology of growth hormone secretion during sleep. The Journal of Pediatrics, 128(5 Pt 2), S32-S37. https://doi.org/10.1016/S0022-3476(96)70008-2
2. Besedovsky L, Lange T, Born J. (2012). Sleep and immune function. Pflügers Archiv: European Journal of Physiology, 463(1), 121-137. https://doi.org/10.1007/s00424-011-1044-0
3. Walker MP, Stickgold R. (2004). Sleep-dependent learning and memory consolidation. Neuron, 44(1), 121-133. https://doi.org/10.1016/j.neuron.2004.08.031
4. Tononi G, Cirelli C. (2014). Sleep and the price of plasticity: from synaptic and cellular homeostasis to memory consolidation and integration. Neuron, 81(1), 12-34. https://doi.org/10.1016/j.neuron.2013.12.025
5. Huttenlocher PR. (1979). Synaptic density in human frontal cortex — developmental changes and effects of aging. Brain Research, 163(2), 195-205. https://doi.org/10.1016/0006-8993(79)90349-4
6. Xie L, Kang H, Xu Q, et al. (2013). Sleep drives metabolite clearance from the adult brain. Science, 342(6156), 373-377. https://doi.org/10.1126/science.1241224
7. Goldstein AN, Walker MP. (2014). The role of sleep in emotional brain function. Annual Review of Clinical Psychology, 10, 679-708. https://doi.org/10.1146/annurev-clinpsy-032813-153716
8. Palmer CA, Alfano CA. (2017). Sleep and emotion regulation: an organizing, integrative review. Sleep Medicine Reviews, 31, 6-16. https://doi.org/10.1016/j.smrv.2015.12.006
9. Short MA, Booth SA, Omar O, et al. (2020). The relationship between sleep duration and mood in adolescents: a systematic review and meta-analysis. Sleep Medicine Reviews, 52, 101311. https://doi.org/10.1016/j.smrv.2020.101311
10. Beebe DW. (2011). Cognitive, behavioral, and functional consequences of inadequate sleep in children and adolescents. Pediatric Clinics of North America, 58(3), 649-665. https://doi.org/10.1016/j.pcl.2011.03.002
11. Temple JL, Bernard C, Lipshultz SE, et al. (2017). The safety of ingested caffeine: a comprehensive review. Frontiers in Psychiatry, 8, 80. https://doi.org/10.3389/fpsyt.2017.00080
12. Kredlow MA, Capozzoli MC, Hearon BA, et al. (2015). The effects of physical activity on sleep: a meta-analytic review. Journal of Behavioral Medicine, 38(3), 427-449. https://doi.org/10.1007/s10865-015-9617-6
13. Okamoto-Mizuno K, Mizuno K. (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology, 31(1), 14. https://doi.org/10.1186/1880-6805-31-14
14. Carskadon MA. (2011). Sleep in adolescents: the perfect storm. Pediatric Clinics of North America, 58(3), 637-647. https://doi.org/10.1016/j.pcl.2011.03.003