Delta is the frequency range up to 4 Hz, Delta is present in the EEG of the very young and people with underlying brain lesions. It is seen in stage 3 and 4 sleep. Delta represent a state of deep dreamless sleep. Delta brainwave states have long been associated with healing. While Delta brainwave states usually only occur in deep sleep, it is possible to train yourself to remain awake while reaching the Delta state to experience even deeper levels of meditation and awareness.
Theta waves range from 4 Hz to 8 Hz and are associated with drowsiness, childhood, adolescence and young adulthood. This EEG frequency can sometimes be produced by hyperventilation. Theta waves can be seen during hypnagogic states such as trances, hypnosis, deep day dreams, lucid dreaming and light sleep and the preconscious state just upon waking, and just before falling asleep. Theta represents a state of deep relaxation and meditation, enhanced creativity, stress relief, light sleep and dreaming. Theta brainwave states have been used in meditation for centuries. Research has proven thirty minutes a day of Theta meditation can dramatically improve a person's overall health and well-being. Theta meditation can diminish the need for sleep.
Alpha waves range from 8 Hz to 12 Hz. It comes from the occipital (visual) and parietal cortex and is characteristic of a relaxed, alert state of consciousness. For alpha rhythms to arise, usually the eyes need to be closed. Alpha represent a state of relaxed mental awareness or reflection. Alpha brainwave states are typically associated with contemplation, visualization, problem solving and accessing deeper levels of creativity. Alpha attenuates with extreme sleepiness.
Beta is the frequency range above 12 Hz. Low amplitude beta with multiple and varying frequencies is often associated with active, busy or anxious thinking, active concentration, playing sports or making a presentation.
Gamma is the frequency range approximately 26-100 Hz. Gamma rhythms may be involved in higher mental activity, including perception, problem solving, fear, and consciousness. Gamma brainwave have received the least attention and research, although more attention is currently being paid to them than in years past. Research has indicated at moments when bursts of precognition or high-level information processing occur, your brainwaves briefly reach the Gamma state.