Electroencephalograms (EEG's) are records of the electrical currents produced at the cell bodies and dendrites of the cerebral cortex of the brain. Deviations from normal EEG patterns can help diagnose epilepsy and other abnormal states. The absence of an EEG is used to signify brain death.
There are normally four types of EEG waves:
1. Alpha waves- best recorded from the parietal and occipital lobes while the person is relaxed and awake with the eyes closed.
2. Beta waves- the strongest of these waves are found in the frontal lobes near the precentral gyrus. They are produced by visual stimuli and mental activity.
3. Theta waves- these waves are emitted from the temporal and occipital lobes, and are common in newborn infants. The presence of these waves in adults generally indicates severe emotional distress, and can be a predictor of the onset of a "nervous breakdown."
4. Delta Waves- are emitted in a general pattern from the cerebral cortex. These waves are common in sleep and in awake infants. The presence of delta waves in awake adults indicates brain damage.