How does your brain wake up from sleep?

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When you are asleep, you can be completely dead to the world. But when you wake up, instantly you can be up and with them. How does the brain turn on awareness or consciousness? This question has baffled scientists for centuries – and continues to do so.

Although scientists don’t have the full answer yet, they are finding clues by studying people’s brains as they transition between sleep and wakefulness.

Looking inside a living brain

One way scientists study activity in the brain is by using a tool called electroencephalography, or EEG. EEG measures electrical signals coming from thousands of brain cells called neurons. The person being studied wears a funny cap connected to a computer. It doesn’t hurt at all. The electrical activity in their brain shows up as wavy lines.

You might think that your brain is switched off – or that you’re relaxing – while you sleep, but in reality it’s on a rollercoaster ride, even if you’re not aware of it. You cycle through four different stages of sleep, each of which shows up as a different pattern on the EEG.

One stage of sleep, called rapid eye movement or REM sleep, is when dreams usually occur. Dreams are interesting because you feel that you are conscious, but you are not conscious in the same way that you are when you are awake.

It turns out that each stage of sleep was also associated with different patterns of chemicals in your brain. These are called neurochemicals and are the ways brain cells communicate with each other.

What scientists know so far

One of the major systems in the brain that wakes you up is called the reticular activating system, or RAS. The RAS is a part of your brain located just above your spinal column. It is about two inches long and the width of a pencil. The RAS acts as a gatekeeper or filter for your brain, ensuring that it does not have to deal with more information than it can handle.

The RAS can understand important information and create neurochemicals that wake up other parts of the brain. It also keeps you awake during the day.

If you have to go to the bathroom in the middle of the night, the RAS senses a signal from your body and flips a switch to wake up your brain – just like a light switch. Signals from outside your body, such as the sound of an alarm clock or a parent waking you up, can also trigger your RAS.

When the RAS switch is turned on, it can take some time to wake up your whole brain and body. This is because it takes a few minutes to clear all the “sleepy” neurochemicals from your brain, which is why you may feel groggy when an alarm clock wakes you up.

But why do you feel grumpier on some days and not on others? When your brain is asleep, it switches between deep and light stages. If your alarm clock goes off during a deeper stage of sleep, it takes longer for all parts of your brain to wake up. You can use the technology to track the stage of sleep you’re in and then wake you up during a light stage, so you’ll feel more refreshed.

Mysteries left to be solved

There is still much to learn about being awake. Although you spend about one-third of your time sleeping, scientists do not fully understand the purpose of sleep.

They know that sleep is vital to health, especially for children whose brains and bodies are still growing. Sleep restores your immune system, improves your memory and supports your mental health. And you might be surprised how many hours of sleep doctors recommend for babies, children and adults.

Although scientists have found some of the pieces, the puzzle of how and why the brain generates consciousness remains unresolved. That’s why the future needs inquisitive scientists – maybe even you.

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This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by: Hilary A. Marusak, Wayne State University and Aneesh Hehr, Wayne State University

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Dr. Marusak is funded, in part, by grants from the National Institute of Mental Health.

Aneesh Hehr does not work for, consult with, share in, or be funded by any company or organization that would benefit from this article, nor has she disclosed any material interests beyond their academic appointment.