While the effects of sleep deprivation are widely recognized, researchers have discovered that sleeping excessively may be harmful to your brain. According to a new study, sleeping more than eight hours each night might impair cognitive function and thinking abilities. The study also found that people who sleep nine hours or more per night tend to have smaller brains than those who sleep fewer hours. The link between excessive sleep and reduced brain size has been noted in other studies as well. For example, a 2013 report published in the Journal of Neuroscience found that when rats were kept awake for several days in a row, their brains tended to shrink. The same study also reported that when these rats were allowed to sleep again, their brains recovered some of its lost volume. So, while it's good to get plenty of rest, too much sleep can be bad for you. If you're finding it difficult to stay awake during work meetings or school classes, make an effort to cut back on your nightly sleep time. This will help your brain function at its best and give you better ability to handle daily challenges.