The electroencephalograph, or EEG, is a machine commonly used by doctors and researchers who want to know what the brain is doing without having to open up someone’s head and look inside. In fact, even if you were to look inside the head, you still couldn’t see the brain “doing” anything — the energy brain uses to operate is not visible. Nevertheless, brain activity can be recorded on an EEG just by taping a few electrodes to someone’s scalp. How is that? The answer is that the brain runs on electrical energy. Individual brain cells, called neurons, regularly discharge tiny electrical impulses among themselves: this is the way they communicate. All these electrical impulses add up to create what are called “brain waves.”