The human brain is the most complex and remarkable organ of the body. It controls everything we do – thinking, learning, and even heart rate. Though the brain makes up only 2 percent of the body’s weight, it uses around 20 percent of its energy. It works 24 hours a day. Even when a person is sleeping, the brain is working hard to keep other organs functioning. Most people think that our brain is more active during the daytime because it needs to deal with a great amount of information. In fact, that’s not true. The brain is far more active when a person is sleeping! However, scientists don’t yet have any explanation for this fact.