What it is. An EEG is a machine that records the electrical activity of the brain.
Who needs one. Your doctor may order an EEG, or electroencephalograph, if he or she suspects some damage in the brain. You may need an EEG if your headaches are accompanied by fainting, loss of consciousness, head injury, or organic brain syndrome.
How it is done. When you have an EEG, a healthcare provider places electrodes in various locations on your shaved scalp. The electrodes are connected to a machine that measures and records the brain's electrical impulses. The recordings appear as patterns that the machine prints out on paper. Certain patterns have certain meanings. For instance, certain patterns could indicate a seizure or the presence of a brain tumor. You won't feel any pain during an EEG.