In 1929 Hans Berger proposed  after extensive studies using an electroencephalogram  that the brain is always in "a state of considerable activity" even when people were sleeping or relaxing In the mid 1990s  Marcus Raichle had demonstrated that the human brain is a glutton  constantly demanding 20 percent of all the energy the body produces and requiring only 5 to 10 percent more energy than usual when someone performs mentally demanding tasks e