Write short notes on EEG.

EEG is short form for Electroencephalogram.
* It is used in the diagnosis of certain neurological and sleep disorders.
* Electrical activity of the brain is recorded in the form of waves. There are 4 types of waves.
* Alpha waves : They occur at a frequency of 8 to 13 cycles per second. They are produced in persons who are drowsy.
* Beta waves : They occur at a frequency of 13 to 40 cycles per second. They are recorded in mentally active and tense persons.
* Delta waves : They occur at a frequency of 3 cycles per second in adults during deep sleep.
* Theta waves : They occur at a frequency of 4 to 7 cycles per second.They are recorded during emotional stress in adults.