What is EEG?To produce an electroencephalograph (EEG), up to 256 electrodes are placed over the skull. They measure changes in the electric field being produced by the brain, and the result is a wave pattern that depends on what the person is doing. An EEG is especially useful for investigating sleep cycles, for diagnosing epilepsy and for studying the relationship between brain activity and mental activity. It is a useful technique, able to detect electrical changes that happen in a few thousandths of a second.
How awake are you?
Your brain wave pattern depends on what you are doing. When you are alert and thinking, your brain is very active and gives a beta-wave EEG pattern. If you close your eyes but stay awake, the EEG shows an alpha wave, while theta and delta waves show you are drowsy or asleep. Different stages of sleep also have different EEG patterns. Strangely enough, REM (rapid eye movement) sleep has an EEG pattern very similar to that of your awake brain - it probably occurs when you are dreaming.
How does epilepsy affect the brain?
People with epilepsy have seizures caused by unusual electrical activity in part or all of the brain. Doctors can use an EEG to measure this activity, and diagnose epilepsy (as seizures can have other causes). Unusual bursts of electric activity can sometimes be detected between seizures, and are called 'spikes'. The location of these spikes in the brain can help doctors decide what type of epilepsy the person has, and so what treatment to use.