Why do we need sleep? Is bedtime just a time for dreaming? Do our brains turn off for the night? What if I told you that scientists recently discovered that our brains may be just as busy at night as they are during the day?

While we sleep, our brains are doing much more than getting ready for the next day. Researchers at the University of Rochester found that the brain may be busy cleaning house -- cleaning out harmful waste materials.

As with many studies, the researchers turned to mice for help. They studied mice that had colored dye injected into their brains. They observed the mice brains as they slept and when they were awake. The researchers say they saw that the brains of sleeping mice were hard at work.

Dr. Maiken Nedergaard led the study. The brain expert says our brains perform two very different jobs. It seems they have daytime jobs. Later they “moonlight” at a nighttime job.

“Moonlighting” is working a nighttime job in addition to a day job. And this study says that is what our brains seem to be doing ? working an extra job at night without additional pay for overtime.

“When we are awake, the brain cells are working very hard at processing all the information about our surroundings. Whereas during sleep, they work very, very hard at removing all the waste that builds up when we are awake."

The researchers say that the waste material includes poisons, or toxins, responsible for brain disorders such as Alzheimer’s disease.

They also found that during sleep, the brain’s cells shrink, or become smaller. This shrinking permits waste to be removed more effectively.

Dr. Nedergaard says these toxins end up in the liver. There, they are broken down and then removed from the body. "So our study suggests that we need to sleep because we have a macroscopic cleaning system that removes many of the toxic waste products from the brain."

The brain’s cleaning system could only be studied with new imaging technologies. The test animal must be alive in order to see this brain process as it happens.

Dr. Nedergaard says the next step is to look for the process in human brains. She said the results demonstrate just how important sleep is to health and fighting disease. The research may also one day lead to treatments to prevent or help fight neurological disorders.

Do you have trouble sleeping? Not being able to sleep is called insomnia. According to the United States National Sleep Foundation, here are some tips for a good night’s sleep:

Go to bed about the same time each night, even on weekends. This helps to “set” your body’s “sleep clock.” Exercise every day. Have a calm, relaxing bedtime routine ? take a warm bath or drink a hot cup of tea.

Try not to take long naps during the day. Periods of sleep during the daytime can interfere with sleep at night. Make sure you have a pleasant environment where you sleep. For most people, a cool, quiet and dark room is best for sleeping.

Avoid using television, computers and other electronic screens before bedtime. Also avoid alcohol, cigarettes and heavy meals before bedtime.