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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? ＿＿（37）＿＿ 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. ＿＿（38）＿＿ 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. Whereas during sleep, they work very, very hard at removing all the waste that builds up when we are awake.
"When we are awake, the brain cells are working very hard at processing all the information about our surroundings. The researchers say that the waste material includes poisons, or toxins, responsible for brain disorders such as Alzheimer's disease. It is not just beauty sleep. The brain needs us to sleep so it can get to work. ＿＿（39）＿＿ 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 that this brain process may be seen as it happens. Dr. Nedergaard says the next step is to look for the process in human brains. ＿＿（40）＿＿ The research may also one day lead to treatments to prevent or help fight neurological disorders.
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. 38 It seems they have daytime jobs. Later they "moonlight" at a nighttime job.
AThey also found that during sleep, the brain's cells shrink, or become smaller.
BWhile we sleep, our brains are doing much more than getting ready for the next day.
CShe said the results demonstrate just how important sleep is to health and fighting disease.
DThe brain expert says our brains perform two very different jobs.正確答案
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