EEG and the brain's state

EEG (Electroencephalography) technology is used to measure brain's electrical vibrations from the surface of the scalp. The resulting EEG pattern will contain frequency elements mainly below 30Hz. The frequencies are categorized into four states as follows:

State Frequency range Amplitude State of mind
Delta 0.5Hz - 4Hz high (up to 200uV) Deep sleep
Theta 4Hz - 8Hz low (5uV - 20uV) Drowsiness (also first stage of sleep)
Alpha 8Hz - 14Hz high (up to 200uV) Relaxed but alert
Beta 14Hz - 30Hz low (less than 10uV) Highly alert and focused

The dominant frequency in the EEG pattern determines what is called the current state of the brain. If the amplitude of the alpha range frequencies is highest, the brain is said to be in the alpha stage. Note that other frequencies still occur; it is not meaningful to give any exact frequency your brain is "operating on."



Maintained by Francis F. Steen, Communication Studies, University of California Los Angeles