The brain is made up of around 100 billion neurons. Though it only makes up 2% of body weight, the brain uses 20% of oxygen, 20% of blood flow, and 40% of total energy. It works at a frequency of around 8 Hz, has a density of 1,038-1,041, and is able to memorize 96 million bits of information daily, making it the most complex structure in the universe that defines who we are.