The Neurobiology of Sleep

We all know how sleeping feels like. From the moment when you start feeling tired, but you already feel better when you think that you are about to hit the pillow. And then you lay your body on the soft, cold sheets, but you suddenly feel warm and fuzzy when the bed starts hugging you. Then you surrender to the hug and let the night slowly take you away. Those moments when you start drifting are the best. You wish they last longer, because you are neither asleep nor awake and you feel like you are floating on a cloud. A nice, fluffy, cuddly cloud, that makes you forget about your problems and worries and just knuckle under your blanket. When we were little, our teachers and parents forced us to go to bed in the middle of the day and we couldn’t understand why they are trying to punish us. Nowadays, we wish the day lasts longer than 24 hours, so we can twirl under the bed sheets a little longer. Unless it’s your wedding day, your morning alarm must make you very jumpy. It signalizes the end of a realm where everything is possible, even though you know it’s just a dream. And that makes you believe that everything may be possible, even if you don’t want to admit it.


Sleeping and Different Species

All species have unique sleeping patterns. Some organisms are suspected to never sleep at all, like some types of fishes and insects. Just like humans, some birds and mammals have the same patterns of REM and non REM sleep. Cats and dogs prefer to sleep for short periods of time, multiple times a day. While humans need to be very comfortable to fall deeply asleep, some species can sleep standing up or hanging down. Flamingos for example, can sleep standing up with their head enclosed in their feathers, while bats sleep upside down, hanging from a branch. We all sleep at different periods of the day. Your cat might sleep all day and feel the urge to get into troubles when you need sleep the most - at night. The duration of the sleep patterns is also very different from species to species. Babies may need to sleep up to 18 hours every day, but their sleeping patterns are inconsistent. The same is the case with elderly. They might wake up early, nap two or three times during the day and go to bed early. An average adult needs from 6 to 8 hours of sleep every day to feel rested, rejuvenated and able to function normally. Bats, cats, chipmunks and giant armadillos need at least 14 hours of sleep every day, some of them may enjoy this phenomenon a little longer, like 19 to 20 hours. Horses need the least sleep, and they can run all day after only 2 hours of good, solid sleepy time.

Sleeping and the Brain

While we are familiar with our human sleeping stages, like REM and non REM, some species don’t have these stages and some of them never dream. Some birds, parrots and certain species of lizards have the most amazing sleeping patterns in the animal kingdom. It’s called unihemispheric sleep, where you can’t fall deeply into sleep because at least one brain hemisphere is always awake. If you ever wander through the woods and spot a lizard with only one open eye, make sure you don’t disturb him, because he’s sleeping. If you wait long enough, you can see when his brain hemispheres switch, because he will open the sleeping eye and close the other one. Although, we sleep with both eyes closed, that doesn’t make our entire brains shut down. Especially before you fall deeply asleep, you can be easily aroused. Scientists have been measuring the brain functions while we are sleeping so that now we can make sure we know exactly how many hours of sleep we need before we wake up. The invention called electroencephalograph was invented in the 50’s, when the student Eugene Aserinsky wanted to learn what happens to our brains while we are sleeping.

If you let a neuroscientist attach an electroencephalograph to your head while you are sleeping, you will discover that all four types of brainwaves are active during each of your sleeping sessions. Some are active more than others, which is why sometimes you can’t wake up with the alarm in the morning. When you are awake but relaxed, the most active brainwaves are the alpha waves. If you try to concentrate and stay focused, the beta waves take over the functions in your brain. Theta and delta brainwaves are the slowest moving waves and they control your brain when you are asleep or trying to. Brainwaves are basically the measured pulsation of the neurons in the brain when they are trying to communicate. Therefore, alpha and beta waves are more faster, because the brain tries to exchange information to make sense of its surroundings. When we are asleep, we don’t use our brain to a great extent, so the neurons exchange less electricity and cause slower brainwaves. During a good night’s sleep, the brain waves switch several times, sometimes causing you to dream, other times awaking you from a bad and scary dream.

The Five Stages of Sleeping

There are five complete stages that enclose a single sleeping cycle. The non REM cycle is completed with the fourth stage, after which you enter the REM sleep stage. Each of the non REM stages can last from 5 to 15 minutes and all together that make about 75 percent of the entire sleeping cycle. All stages happen one after the other, making a cycle of around 90 minutes, and when the cycle ends, it starts all over again. Scientists tried to prove which stage is more important than the others, but it turns out that a completed cycle is essential for assuring a healthy mental human state.

The Non REM Stages

As soon as you close your eyes trying to fall asleep, the first stage of non REM sleep begins. At this stage, you are neither awake nor asleep, and you are sort of in between of a light sleeping process and wakefulness. The brainwaves start to slow down in this phase, but you are still aware of your surroundings, including sounds, smells and light. You can be easily aroused in the first stage and if you are awakened, you will not feel like you have been asleep at all. The feeling that you are falling down a cliff can occur in this stage, but most of the time muscle contraction are more common. This stage lasts for 10 minutes or less.

In the second stage, your muscles start to contract and relax simultaneously, your breathing rate starts to even out and your body temperature is dropping. That is why it is best to sleep in a room with colder temperature, so that your body doesn’t have to struggle to enter this stage. This stage is a stage of delirium, where you may start talking or mumble something non comprehensible. You become disengaged from your surroundings, responding to sound, light and smell in a remote manner.

While the first and second stage of the non REM sleep is led by theta waves, the third stage is when delta waves are most prominent. This phase is the transitional stage between lighter sleep and the deep sleep cycle. By now, your muscles are more relaxed, your blood pressure will drop and blood is supplied to every part of your body increasingly. You can’t be easily awakened in this stage, and if you are, you will feel disoriented and uneasy.

The fourth stage is when even deeper sleep takes over your body and brain. For restorative bodily functions, this stage is most important. Hormones are released in this stage, your body recovers its energy, your tissues are re-energized and growth and healing befall. Your dreams and nightmares might start evolving now and in the REM sleep you may be able to wake up from them or continue dreaming, if they are pleasant of course.

What is Rapid Eye Movement?

The acronym REM stands for Rapid Eye Movement. This is the final stage of each sleep cycle, which takes around 25 percent of the entire sleeping cycle. This stage happens around 40 to 60 minutes after you fall asleep and lasts around 10 minutes. The first REM phase lasts around 10 minutes, but later in the night it may last longer, reaching a whole hour if you sleep eight or more hours. In this stage, your muscles are still asleep, but the brain activity starts to increase. During this phase you will start breathing more erratically, your heart rate will rise and your eyes will move rapidly back and forth, thus the name Rapid Eye Movement. Penile erection and vaginal lubrication may also occur in this stage, as well as the discharge of the hormone cortisol. Vivid dreaming and hallucinating happens during this period, and some scientists refer to this stage as a third level of existence, because dreams seem very real in this phase. This sleep phase is sometimes called paradoxical sleep, because muscle immobility and increased brainwave activity may happen at the same time. Experts think that our bodies are somewhat paralyzed during a REM sleep, to avoid hurting ourselves and others in this unconscious state.

How Much Sleep Do We Need?

While we all feel better after a total 9 hours of sleep, most of the time your body and brain may need much less than that. Make sure you have at least 2 complete cycles of REM and non REM sleep every night, and you will be able to wake up fresh and full of energy. Too little sleep may cause depression, immune system impairments, weight gain, impaired cognitive functions and fatigue. To make the cycles more successful avoid drinking alcohol and coffee before going to bed. Digesting food may also take much energy away from the body, so eat at least two hours before you fall asleep. Taking power naps can also increase your energy. A 20 minute nap will get your body through the first two stages, which will be enough rest to elevate your mood, improve your concentration and alertness. More than an hour spent napping will complete the full five stages of sleep, which will make you feel rested, but you will need more time to adjust from the disorientation and grogginess. A 45 minute nap may be just the kind of snooze you need to go through your day without reducing your brain’s sensory processing and creative thinking. Some people say that sleeping is a luxury they don’t have, but regular sleeping process can improve your ability to think, reason and act. A well-rested body will also fend off colds, infections, premature aging and many mental disorders, so make sure you have enough time each day for a steady beauty sleep.


QR Code
QR Code neurobiology_of_sleep (generated for current page)