An EEG is the most important test to identify epilepsy. The EEG picks up electrical activity in the brain and draws squiggly lines representing them on paper or a computer. These squiggles are called your brain waves. The stronger the electrical activity in each part of the brain, the taller the waves will be. Tall waves on the EEG are called "spikes". Finding spikes on a person's EEG means that that person's brain cells are firing very strongly and often. If brain cells (neurons) fire strongly and often, it is likely that the person will have seizures.
This is a drawing of a girl having an EEG.
This is the difference between brain waves and spikes.
This is an EEG machine. Notice the little wires wrapped in the towel. Those are the leads that are pasted onto the patient's head. Then they are plugged into the "head box" the rectangular box to the right of the computer screen. The computer records and shows the electrical activity of the area of the brain that is under each wire seperately, so the doctor can find out where the seizure activity is coming from in the brain. The EEG is so sensitive that it is picking up movement in the room - the black vertical stripe on the computer screen was from when I wiggled on the bed. And the leads are not even attached!