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 |
State of Mind |
| Delta |
0.5 Hz - 4 Hz |
Deep Sleep |
| Theta |
4 Hz - 8 Hz |
Drowsiness (also first stage of sleep) |
| Alpha |
8 Hz - 14 Hz |
Relaxed but Alert |
| Beta |
14 Hz - 30 Hz |
Highly alert and focused |
The dominant frequency in the EEG pattern determines what shall be called the current state of the brain. If the amplitude of the alpha range frequencies is highest, then the brain is said to be in the alpha stage. Note that other frequencies still exist and it is impossible to give any "exact frequency your brain is operating on."
However, later references to the brain states use the simplification of assuming that such a single frequency exists.
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