An EEG may be done to study seizures, study sleep disorders, or help find the location of a tumor, an infection, or bleeding. An EEG technologist attaches a cap with fixed electrodes on your head. (An EEG can also be done without a cap by using several individual electrodes.) The electrodes are hooked by wires to a machine that records the electrical activity inside the brain. The machine shows the electrical activity as a series of wavy lines on a computer screen.