The EEG shows patterns of normal or abnormal brain electrical activity. Some abnormal patterns may occur with a number of different conditions. For example, seizures or certain types of waves may be seen after head trauma, stroke, brain tumor, or seizures. Certain other patterns indicate a tendency toward seizures. Generalized epilepsy is suggested by spike-and-wave discharges that are widely spread over both side of the brain, especially if they begin in both sides at the same time.