Have you ever wondered what happens when you close your eyes and drift off to sleep? We spend about a third of our lives sleeping, yet it remains one of the most mysterious parts of our daily routine. Even scientists are still trying to figure out exactly why we need sleep. For a long time, people thought our brains just turned off during sleep, but now we know that sleep is one of the most important things we do.
While it might seem like we’re doing nothing when we sleep, our brains are actually very busy. Sleep is controlled by a complex system of chemical and electrical signals in our brain. During the day, certain chemicals keep us awake and alert. But as the day goes on, a substance called adenosine builds up, making us feel sleepy. Our brain has a special “clock” that helps us sync with the 24-hour cycle of day and night, known as circadian rhythms. This clock is influenced by light, which is why we feel sleepy when it gets dark.
As night falls, our brain tells a gland to release a hormone called melatonin, which helps us feel sleepy. This is why we often feel tired when it’s dark. Interestingly, our body temperature drops slightly when we sleep, which is why some people like to sleep with their feet sticking out of the covers!
In today’s world, darkness is becoming rare due to artificial lights. This can confuse our brains, making it harder to fall asleep. Exposure to bright lights at night can stop the release of melatonin, leading to sleep problems. This disruption can have serious health effects, including links to depression, heart disease, and other illnesses.
Before artificial light, people often had two sleep periods: they would sleep for a few hours, wake up for a bit, and then go back to sleep. Experiments show that without artificial light, people might naturally return to this pattern. However, most of us now sleep in one long stretch, and many of us don’t get enough sleep. Teenagers, for example, often get only five hours of sleep on school nights, which is far less than they need.
Even though we don’t fully understand why we need sleep, we know it’s crucial for life. Animals that don’t get enough sleep can suffer severe consequences, even death. Sleep helps with cellular repair and memory consolidation, allowing our brains to process information and solve problems more effectively. Sleep-deprived people struggle with learning and creativity.
One of the biggest mysteries is how sleep evolved. Sleeping makes animals vulnerable to predators, yet it’s essential. Some animals have adapted in fascinating ways, like dolphins, which sleep with one half of their brain at a time to avoid drowning. Sleep is so widespread in the animal kingdom that it likely has ancient origins, possibly dating back 700 million years.
Understanding sleep better can help us appreciate its importance and encourage us to make more time for it. If you’re curious to learn more, there are great resources like “Dreamland: Adventures in the Strange Science of Sleep” by David Randall, and various educational videos that explore the science of sleep further. Stay curious and make sure to get enough rest!
Track your sleep patterns for a week. Note the time you go to bed, the time you wake up, and how you feel each morning. At the end of the week, analyze your data to see if you notice any patterns or areas for improvement. Share your findings with the class and discuss how your sleep habits compare to the recommended sleep duration for teenagers.
Conduct a simple experiment by altering your exposure to light before bedtime. For two nights, avoid screens and bright lights for an hour before sleep. For the next two nights, use screens or bright lights as usual. Record how easy it is to fall asleep and how rested you feel in the morning. Discuss your results with classmates to understand the impact of light on sleep.
Choose an animal and research its sleep habits. How does it sleep, and what adaptations does it have for sleep? Present your findings to the class, highlighting any unique sleep behaviors or evolutionary traits. Compare these with human sleep patterns and discuss the possible reasons for these differences.
Imagine you are an interior designer tasked with creating the perfect sleep environment. Consider factors like lighting, temperature, and noise. Create a design plan or drawing of your ideal sleep-friendly bedroom. Present your design to the class and explain how each element contributes to better sleep.
Participate in a class debate on the topic: “Is sleep more important than diet and exercise for overall health?” Prepare arguments for both sides, using evidence from the article and additional research. Engage in the debate, and afterward, reflect on what you learned about the importance of sleep in maintaining a healthy lifestyle.
**Sanitized Transcript:**
[MUSIC][MUSIC] For many of us, the worst moment of every day goes something like this… [ALARM CLOCK NOISE] That noise marks our daily return from the mysterious world that we call sleep. We spend a third of our lives asleep, yet, other than the odd snapshot of a dream here and there, most of us have no idea what happens after we close our eyes. Luckily, we’re in good company, because there’s also a lot scientists don’t know about sleep too. For a long time, it was just something that happened; everyone assumed that our brains were hitting the reset button and just turning off for a while. But in the past few decades, it’s become clear that sleep might be the single most important behavior that humans and other animals experience.
It might seem like we don’t do much while we’re asleep, but neuroscience tells a different story. Human sleep patterns are controlled by two competing networks of chemical and electrical signals in the brain. During our waking hours, neurotransmitters released deep within our brain keep our cerebral cortex alert and primed for consciousness. But throughout the day, as our neurons break down ATP for energy, the byproduct adenosine builds up and activates sleep control neurons near the hypothalamus. A special region in the center of our brain acts as our master biological clock. Light-sensitive cells in our retinas feed signals deep into that brain region, training neurons to sync up with Earth’s 24-hour cycle of day and night. These circadian rhythms are the control switch that tells us when to feel sleepy or awake.
As the world goes dark, this master switch tells our pineal gland to increase levels of the hormone melatonin in the bloodstream, sort of like a chemical lullaby. Feelings of fatigue set in, body temperature lowers slightly; that heat loss is actually why many of us like to fall asleep with our feet sticking out of the covers—true story! Together, all this neurochemistry sends one clear message to our bodies: when it’s dark, it’s time to go to bed.
Unfortunately, in modern times, darkness is increasingly rare. In the United States, 99 percent of people live in areas that meet standards for light pollution, and we’ve got one person to thank for that: Thomas Alva Edison. Edison thought sleep was lazy, unhealthy, or inefficient, even though he took several naps a day. But despite that hypocrisy, his work and the idea of working more and sleeping less changed our world forever. Illuminating the night became a sign of economic progress, and humankind was no longer at the mercy of nature’s clock. Or so we thought.
Artificial light can have serious effects on our sleep cycle. When we’re exposed to bright light at night, our brain doesn’t know better than to think the sun is shining. This can be very confusing, preventing the release of melatonin and the onset of sleep. Depression, heart disease, diabetes, and cancer have all been linked to chronic overexposure to artificial light. Until just a couple hundred years ago, it was common for people to fall asleep right after the sun went down, snooze for a while, wake up around midnight, where they would read or study or do other activities, then go back to sleep until morning.
Modern experiments have suggested that if people are kept away from artificial light, their bodies will return to this pattern of first and second sleep, yet most of us insist on sleeping the whole night through. What’s worse, our circadian rhythms are so tuned to day and night that if we stay up past our usual bedtime, we don’t wake up later; we just tend to sleep less. As a result, we’re massively sleep-deprived. Most adults average just six and a half hours a night. Teenagers average just five hours on school nights, which is half of what they need. To fight this chronic exhaustion, we turn to stimulants like caffeine to help our brains ignore that buildup of adenosine, and then to fight the stimulants, many people rely on alcohol, which just sedates us; it doesn’t even help with real, restful sleep. This vicious cycle is worth literally billions of dollars a year.
So what is sleep for? In short, we’re not really sure, but we know it’s essential to life. Animals deprived of sleep for a long enough time will have seizures and can literally die from exhaustion, plus a significant percentage of our genes are linked to circadian rhythms. Still, there’s no consensus on exactly why our bodies need sleep. We’re definitely less active at night, but considering we only burn about 100 fewer calories while sleeping, it’s not a very good energy-saving strategy overall. We definitely do a lot of cellular repair, protein synthesis, and general biological upkeep while we’re in dreamland, but it’s not like we don’t do that stuff when we’re awake too.
Another theory suggests that our bodies use time asleep to flush out all the neuro-waste, removing waste products that build up in our neurons and brain cells. And decision-making regions of our brain, like the prefrontal cortex, don’t get any downtime while we’re awake; even if you’re totally relaxed and you think your mind is clear, your prefrontal cortex is still active. Just try and think about nothing. Go ahead. See? You’re thinking about not thinking. Sleep seems to be the only time for this region to power down and get a break.
The greatest benefit of sleep may lie in processing information and consolidating memories from throughout the day, letting the brain do all the rewiring that is necessary for better thinking. Sleep-deprived people do worse when learning new tasks and are less able to process new information, whereas a good night’s rest appears to make us more creative so we can come up with solutions to new problems that we haven’t seen before.
Perhaps the biggest mystery is how sleep evolved in the first place. Sleeping animals are easy targets for predators, so you’d think evolution would have come up with something better. But it hasn’t. There’s no way to get around the need for sleep. Some animals have come up with interesting ways to deal with the inconvenience of sleeping, though. Dolphins obviously can’t nod off without drowning, so they only sleep with one half of their brain at a time, swimming along using the half of their body that’s still awake. Before baby dolphins learn that trick, they take adorable little naps while their parents keep them afloat.
Sleep or similar patterns of rest are seen so universally throughout the animal kingdom that they must have an ancient origin, and one clue comes from a tiny, ocean-dwelling worm. Every night, these worms swarm near the surface of the ocean to feed, and every day they sink down deep to avoid light and predators. The worms have special daylight-sensing cells on their back, just like the ones in our eyes. When it’s dark, those cells trigger the production of melatonin, just like in our brains. As the melatonin builds up, tiny hairs on their bodies stop beating, and the worms begin to sink, just in time for the sun to come up. As the melatonin disappears throughout the day, the hairs begin beating again, and they swim back up to the surface to do it all over again.
Sleep might have evolved 700 million years ago, the last time we shared a common ancestor with that tiny worm. It’s pretty important, so maybe we should all make a little more time for it. If you want to learn more about the science of sleep, one book that really helped me is “Dreamland: Adventures in the Strange Science of Sleep” by David Randall. And also, be sure to check out this half-hour playlist from our friends at The Good Stuff that digs even deeper into what our brains are doing while we’re asleep, plus Craig goes to a sleep lab to find out how to get a better night’s rest. Oh, and over at BrainCraft, Vanessa has a video with some scientific tips on how to beat jet lag. In fact, just make sure you’re subscribed to The Good Stuff and BrainCraft; they are awesome. Links to all that down in the description. Stay curious.
Sleep – A natural state of rest for the body and mind, during which consciousness is suspended and the brain and body undergo various restorative processes. – Getting enough sleep is important for teenagers because it helps their brains function properly and improves their ability to learn and remember new information.
Brain – The organ in the body that serves as the center of the nervous system, responsible for processing sensory information and controlling behavior. – The human brain is capable of forming new connections every time we learn something new, which is essential for memory and learning.
Melatonin – A hormone produced by the pineal gland in the brain that helps regulate sleep-wake cycles. – As it gets darker in the evening, the brain releases more melatonin, signaling to the body that it is time to prepare for sleep.
Light – Electromagnetic radiation that is visible to the human eye and is crucial for regulating biological processes such as the sleep-wake cycle. – Exposure to bright light in the morning can help reset your internal clock and improve your sleep patterns.
Rhythms – Regular, repeated patterns of biological processes or behaviors, often influenced by environmental factors like light and temperature. – Circadian rhythms are natural, internal processes that regulate the sleep-wake cycle and repeat roughly every 24 hours.
Chemicals – Substances produced by the body that can affect mood, behavior, and physiological functions. – Neurotransmitters are chemicals in the brain that transmit signals between nerve cells, playing a key role in mood regulation and mental health.
Depression – A mental health disorder characterized by persistently low mood, loss of interest in activities, and other symptoms that affect daily functioning. – Research suggests that imbalances in certain brain chemicals can contribute to the development of depression.
Patterns – Repeated or regular arrangements of elements or events, often observed in biological systems and behaviors. – Scientists study sleep patterns to understand how different factors, like stress or diet, can affect the quality of sleep.
Evolution – The process by which different kinds of living organisms develop and diversify from earlier forms over generations. – The evolution of the human brain has allowed us to develop complex language and problem-solving skills.
Memory – The mental capacity to store, retain, and recall information and experiences. – Sleep plays a crucial role in consolidating memory, helping us retain what we have learned during the day.
