Electroencephalography (EEG) Home A-Z Health Information Health Library A-Z Electroencephalography (EEG) Overview Electroencephalography is a non-invasive (painless) neuroimaging technique that measures the electrical activity of brain through electrodes placed on scalp. The activity in the brain evolves as the brain develops. In a sleep deprived state, the chances of abnormal activities in the brain being recorded are higher. EEG is performed under video recording to correlate the electrical activity with simultaneous abnormal body movements. Sometimes, prolonged EEG recording is also done for 48–72 hours to isolate the exact focus of abnormal activity. Method Various electrodes are placed in frontal, parietal, temporal and occipital areasActivities in these areas are recordedVarious manoeuvres such as photic stimulation, hyperventilation, eye opening and closure are performed during the recordingThe responses are recorded to find any abnormality in the brain activity Normal EEG Waves Delta waves (0.5–4 Hz): during deep sleep and unconsciousnessTheta waves (4–8 Hz): during drowsiness and early sleepAlpha waves (8–12 Hz): during relaxed state with eyes closedBeta waves (13–30 Hz): during alert, thinking state Indications Epilepsy and seizures, status epilepticusSleep disordersComa, encephalopathyEncephalitis and other brain infectionsMetabolic disorders causing altered sensoriumHead injuryAdditional testing for brain death