Figure – Brain wave patterns (gamma-waves above 40 Hz). Gamma waves – 40 hz above – these are use for higher mental activity such as for problem solving, consciousness, fear. Beta waves – 13-39 Hz – these are for active thinking and active concentration, paranoia, cognition and arousal. Alpha waves – 7-13 Hz – these are for pre-sleep and pre-wake drowsiness and for relaxation. Theta waves – 4-7 Hz – these are for deep meditation, relaxation, dreams and rapid eye movement (REM) sleep. Delta waves – 4 Hz and below are for loss of body awareness and deep dreamless sleep (source: Medical School, link).