Brainwaves are measured in Hertz (Hz - cycles per second), and can be measured using devices such as an electroencephalograph (EEG) machine. The generally recognised frequency bands are as follows:
Delta brainwaves (> 4Hz)
Delta waves are produced during deep (dreamless) sleep, and the experience of a predominantly delta brain state while awake is rare among untrained people. Brainwave entrainment can make it easier to access the delta state while awake. Delta brain waves are linked with bodily healing and regeneration, as well as the experience of very deep trance and certain ‘altered’ states of consciousness.
Theta brainwaves (4 - 7 Hz)
Theta waves are produced during dreaming sleep and in the state between sleeping and waking. They’re also experienced by meditators in a trance state. The theta state is linked with some altered states of consciousness, as well as with the experience of insights and inner wisdom – perhaps because the subconscious mind may be more accessible in this state.
Alpha brainwaves (8 – 12 Hz)
Alpha waves are produced when we’re relaxed and not focusing on anything in particular. They may be associated with creative thought, and their production is a sign of physical and mental balance; people who are ill or suffering from anxiety, depression etc. may produce fewer alpha waves than normal.
Beta brainwaves (13 - ~25 Hz)
Beta waves are produced when we’re awake, alert, and highly focused. People who have trouble with focus and concentration may produce fewer beta waves than normal. However, excessive beta production is linked with anxiety and similar disorders.
Gamma brainwaves (< 25 Hz)
Gamma brainwaves are high frequency waves that are not well understood (and some researchers dispute their existence as a distinct type). However, they seem to be linked with the experience of unusual states of consciousness such as the transcendental state, with its feelings of moving beyond the limited sense of ‘me’, and becoming part of something greater.
