" Incredibly, the human brain does all of its mega-computing on roughly 20 watts of power, which is the equivalent of a very dim light bulb. By comparison, a supercomputer capable of a similar rate of computation requires 200,000 watts – in other words, it is 10,000 times less energy-efficient than the human brain. Despite the human brain’s efficiency, however, it is extraordinarily energy hungry compared with all other tissues. While accounting for only 2 to 3 per cent of the mass of an adult, it consumes about 20 per cent of the body’s oxygen. "

― Marcus Chown , Infinity in the Palm of Your Hand: Fifty Wonders That Reveal an Extraordinary Universe