Why do we sleep?

By: Charles W. Bryant

Getting More Sleep Image Gallery The old joke is that we sleep to cure sleepiness. See more sleep pictures.
Biggie Productions/Getty Images

Most adults who aren't insomniacs love it when that time of the night rolls around. At last, they can leave the worries of the day behind and fall into a lovely, relaxing sleep. A night of sawing logs can leave you feeling refreshed and ready for the coming day. Some people even make better decisions after "sleeping on it" for the night. In fact, an easier article to write might be "why do we love to sleep?." The trouble is, after all these years and millions of hours of research, science still isn't exactly sure why we sleep. There's an old joke among sleep scientists that the purpose of sleep is to cure sleepiness. But humor aside, there are a few theories on the matter.

One theory is that sleep is our brain's opportunity to file away or discard memories, thoughts and events from the previous day. Think of your brain as a desktop computer, and sleep as your way of organizing everything after a long day of work. Some of the files you may want to store away as permanent memory, but others you might want to put directly into the recycling bin. A study performed on lab rats found the same neurons that fired when a rat was completing a task (like working its way through a maze) also fired when the rat was sleeping [source: Gorman]. This indicates that a review process may take place while we sleep. (However, it was also learned that the same neurons were reactivated during periods of rest.)


The filing theory jibes with the fact that we often wake up with a clearer head. Have you ever decided to "sleep on it" before you made a tough decision? There might be something to that strategy. It's been theorized that, during the night, some of the unnecessary emotional responses and extra information that clouded your thoughts are put into the recycling bin, leaving only the information necessary to make the decision. The next morning you awake with a crystal clear perspective on something that had previously seemed muddled.

But that's not the only theory about the function of sleep. Find out more on the next page.


Function of Sleep

You may think that sleep's function is to give your body a break, but you'd be wrong. Our muscles, and body in general, do need rest, but actual sleep doesn't contribute anything to the process. The body only knows when it's at rest; it doesn't care whether you're sleeping or just relaxing in your recliner. But that doesn't mean that your brain doesn't need rest as well. That's why many researchers believe that sleep is just that -- a chance for parts of your brain to take a break. It's an opportunity for your neural connections to strengthen and recharge. However, even if there's some truth to this, science hasn't pinpointed the exact reason why sleep facilitates it. Some scientists feel sleep research has been overanalyzed, and that researchers are simply unwilling to accept the notion our brains need a break.

For example, the head of sleep research at the Walter Reed Army Institute of Research posits that the brain simply gets tired. He backs up his theory with data that shows the brain experiences a dramatic drop-off in performance after it's been awake for more than 24 hours. The brain runs on glucose, and test results show that even when there's plenty of glucose available, after the brain has been awake for a full day, it simply doesn't use it. After the 24 hour window, the use of glucose stabilizes, but the brain's performance continues to suffer. No one is sure why this happens, but the idea that the brain runs on a cycle is gaining credence. It appears the brain literally needs sleep in order to refuel.


We're not there yet, but we're closer than ever to uncovering the mysteries of what exactly happens when we sleep. Perhaps one day science won't have to fall back on its old joke: "We need sleep to cure sleepiness."



Health > Diabetes > Sleep
Health > Aging Process > How do my sleep habits change as I age?
Health > Sleep Basics > Can melatonin help you sleep better?
Health > Sleep Basics > Sleep Pictures
Health > Sleep Journal > Sleep Schedule
Health > Sleep Disorders > Dangers of Sleep Apnea
Health > Sleep Journal > Sleep Deprivation
Health > Sleep Disorders > Do you need sleep drugs?
Health > Sleep Basics > The Get Better Sleep Quiz
Health > Sleep Disorders > How Sleep Deprivation Works
Health > Sleep Journal > I Can't Sleep Because I'm Worried About Not Sleeping
Health > Sleep Basics > Is sleep that important?
Health > Sleep Basics > Avoiding Sleep Deprivation
Health > Sleep Journal > Sleep and Smoking
Health > Sleep Journal > Sleep and Aging
Health > Alternative Medicine > Natural Sleep Aids
Health > Sweating and Odor > Sweating While Sleeping
Health > Baby Care > Baby Won't Sleep? 5 Tips From a Baby Sleep Coach
Health > Modern Medical Treatments > Sleep Apnea Treatments
Health > Sleep Basics > How Sleep Consolidates Our Memories
Health > Sleep Basics > How are sleep and heart disease related?
Health > Sleep Basics > Why do we sleep?
Health > Teenage Health > Helping Sleep-deprived Teens
Health > Skin Cleansing Tips > Is it bad to sleep with my makeup on?
Health > Osteoarthritis > How does sleep affect osteoarthritis?
Health > Sleep Basics > Will you die if you never sleep?
Health > Sleep Disorders > Does sleep deprivation lead to risky decisions?
Health > Sleep Basics > What Happens When We Sleep?
Health > Sleep Journal > Creating the Right Sleep Environment
Health > Sleep Basics > 5 Effects of Sleep Deprivation
Health > Sleep Disorders > 9 Most Common Sleep Disorders
Health > Sleep Journal > Sleep In the Modern World
Health > Baby Care > Safe Sleeping For Your Baby
Health > Sleep Disorders > Why Some People Can't Sleep Without a Fan
Health > Sleep Basics > Why Socks Help You Sleep Better
Health > Sleep Basics > Do Weighted Blankets Help With Sleep?
Health > Baby Care > More Babies Are Sleeping in Boxes — and That's a Good Thing
Health > Sleep Basics > Will we learn to live without sleep?
Health > Sleep Disorders > Does Sleeping On Your Side Stop Snoring?
Health > Headache > How do my sleep and rest patterns affect my headaches?
Health > Sleep Disorders > How Do You Sleep When Sailing Solo for 4,000 Miles?
Health > Sleep Basics > Can Military Meditation Techniques Help You Fall Asleep Fast?
Health > Sleep Journal > Many of My Sleep Problems Are Due to Bad Habits
Health > Sleep Basics > 5 Health Risks of Too Little Sleep
Health > Sleep Basics > Can you die if you don’t sleep?
Health > Sleep Disorders > 10 Signs You May Be Sleep Deprived
Health > Sleep Basics > Yes, You Can Catch Up On Your Sleep!
Health > Sleep Disorders > Why Are You So Tired? 5 Most Common Sleep Mistakes
Health > Weight Loss > Why do I lose weight while I sleep?
Health > GERD > How do sleep and rest patterns affect GERD?
Health > Sleep Basics > How many hours of sleep do you really need?
Health > Sleep Basics > One Simple Way to Get More Sleep: Lower the Thermostat
Health > Sleep Basics > How to Fall Asleep
Health > Sleep Journal > Time For a New Mattress?
Health > Sleep Journal > Secrets of the Siesta and High-Tech Mattresses
Health > Sleep Disorders > Can You Fall Asleep With Your Eyes Open?
Health > Sleep Disorders > Why Do People Fall Asleep in Movie Theaters?

Lots More Information

Related Articles


  • Braun, David. "Why do we Sleep? Scientists are Still Trying to Find Out." National Geographic. 2010. (Aug.13, 2010)http://blogs.nationalgeographic.com/blogs/news/chiefeditor/2009/08/why-we-sleep-is-a-mystery.html
  • Gorman, Christine. "Why We Sleep." Time. Dec. 17, 2004. (Aug. 13, 2010)http://www.time.com/time/magazine/article/0,9171,1009765-1,00.html
  • Schaffer, Amanda. "Why Do We Sleep?" Slate. March 26, 2007. (Aug. 13, 2010) http://www.slate.com/id/2162475/entry/2162476/
  • "Why Do We Sleep, Anyway?" Harvard. 2010. (Aug. 13, 2010) http://healthysleep.med.harvard.edu/healthy/matters/benefits-of-sleep/why-do-we-sleep