Wave patterns form during EEG recording
Delta waves: The frequency of Delta wave is below 4 Hz. It is the highest in amplitude and the slowest waves. It originate normally in adults during sleep. It is also seen normally in babies. It can also be observed in patients during coma.

Theta waves: The frequency of theta wave range from 4 Hz to 7 Hz. It is seen normally in young children. It may be seen in older children and adults under stress or during meditation. Excess theta for age represents abnormal activity.

Alpha waves: The frequency of alpha wave range from 7 Hz to 14 Hz. An awake but resting person produces alpha wave. Hans Berger termed “alpha wave” when he saw the first rhythmic EEG activity. This was the "posterior basic rhythm" seen in the occipital regions of the brain. It arises with closing of the eyes and with relaxation, and weakens with eye opening or mental labour. In addition to the posterior basic rhythm, there are other normal alpha rhythms such as the “mu rhythm” which arises when the hands and arms are indolent.

Beta waves: The frequency of beta wave range from 15 Hz to about 30 Hz. During extreme mental activity, beta wave initiates from frontal and parietal regions. Beta activity is closely linked to motor behaviour and is generally weakened during active movements. An alert wide awake person shows unsynchronised beta wave.

Gamma waves: The frequency of gamma wave is nearly 30–100 Hz. Gamma rhythms represent binding of different populations of neurons together into a network for the purpose of carrying a certain motor function.

Mu waves: The frequency of mu wave is 8–13 Hz. It partly overlaps with other frequencies. It denotes the synchronous firing of motor neurons in rest state.
Deviations from normal pattern indicate brain disorder and change in physiological state of brain. EEG can diagnose epilepsy, brain tumour, abscess, sleep disorders, metabolic and drug effects on brain.