*1.3.2 Beta (β) waves*

Its frequency ranges from 14 Hz to about 30 Hz. Beta activity is a "fast" activity and is also called normal rhythm activity. It is usually seen on both sides of the hemisphere in symmetrical distribution and is most evident in the frontal areas. Sedative-hypnotic drugs affect this activity [7]. It may be missing or reduced in regions of cortical damage. It is accentuated in patients who are very anxious or have their eyes open.

### *1.3.3 Theta (θ) waves*

It has a frequency range from 4 to 7 Hz and is classified as "slow" activity. It is found in every person during sleep and in meditation. It can be seen in the state of arousal for adults [7]. Excess theta in adults represents abnormal activity.
