A normal EEG reading indicates that you have a normal pattern of brain activity.
For example, if your brain is working normally, a brainwave pattern called an alpha rhythm should be seen when you are sitting quietly with your eyes closed. When you open your eyes, the alpha pattern should either disappear altogether or become less prominent.
EEG results are often normal because recording a person’s brain activity during the times it is abnormal is difficult. For example, someone with epilepsy will often have a normal EEG result because their brain activity only alters during an epileptic fit.
Therefore, further EEG testing, such as an ambulatory EEG, may need to be carried out. An ambulatory EEG involves recording your brain activity throughout the day and night, over a period of one or more days. This will enable doctors to assess your brain activity while you are having a seizure.
An abnormal EEG reading occurs when abnormal electrical brain activity is detected. Some people with epilepsy may have abnormal brain activity between attacks, not just when they are having seizures.
A small number of people who do not have epilepsy may also have an abnormal EEG result. This may indicate that you have a different condition that is affecting your brain activity, such as encephalitis (brain inflammation that is often caused by infection).
Your EEG results will help your doctor decide which course of treatment is best for you. If you have epilepsy, the results may also help identify what is triggering your seizures so that you can take preventative measures.
For example, if your EEG results show that your epilepsy is photosensitive (triggered by flashing lights), you can avoid situations where there is likely to be bright, flashing lights, such as nightclubs, discos and flickering television screens.