The human brain is the very core of our existence. It is the body’s control center. As well as keeping the body working smoothly, it is also responsible for our thoughts, feelings, and memory. The brain weighs approximately three pounds and is composed of tens of billions of cells; these nerve cells, or neurons, communicate with each other in an orderly way. The human brain is a grey organ about the size of a grapefruit. It hardly seems to have more than a few separate parts. Yet everything we know is stored there; everything we do, think, feel and dream is made possible by this intricate piece of machinery.