The brain generates weak electrical impulses representative of its particular activities. As recorded by the electro-encephalograph (EEG), they fall into particular levels assigned Greek letters.

• Beta, at 14 to 28 cycles per second, is our normal waking state including focused attention, concentration, thinking, etc.
• Alpha, 8 to 13 cycles, is the next level down characteristic of relaxation, alert receptivity, meditation and access to the subconscious mind. It is at 8 cycles per second, the border between alpha and theta, that Trance occurs.
• Theta, 4 to 7, is lower yet and occurs just before (hypnopompic) or after (hypnagogic) sleep and is characteristic of light sleep, deep meditation, dreaming, vivid imagery, and high levels of inner awareness.
• Delta, 1 to 3, is characteristic of deep dreamless sleep.
• 0 to 0.5 is the state of death or unconsciousness.