I would rate Anna Wise as one of the foremost authorities on the topic of brainwaves. Her research is excellent as is her book on the topic. Our brain is designed as an alchemical 'machine' and it fascinates me.
The following information is based on her discoveries:
Brainwaves - and what they represent (part 1)
Brainwaves can be categorized according to their frequency:
(100 - 38 Hertz = cycles per second)
(38 - 15 Hz)
(14 - 8 Hz)
(7 - 4 Hz)
(3 - 0,5 Hz)
Although logical thinking is often attributed to the left hemisphere and intuitive and creative activities are seen to be located in the right hemisphere, the Mind Mirror EEG in most people is quite symmetrical. Both hemispheres are very well connected, and even though there are brain activities that can clearly be located in one hemisphere (e.g. speech), most of the time both hemispheres are active.
The Mind Mirror display shows the brain waves according to their frequencies from top (38 Hz) to bottom (0.5 Hz). The strength of the signal (amplitude) is determined in how far from the middle the curve reaches outward.
Gamma brainwaves (100 - 38 Hz) were detected later than the other brainwaves, less is known about them so far. They have been seen in states of peak performance (both physical and mental), high focus and concentration and during mystic and transcendental experiences. A lot of research is currently being done on gamma brainwaves in the 40 Hz range during meditation. One of the characteristics of gamma waves is a synchronisation of activity over wide areas of the brain.
Gamma brainwaves are not easy to detect because of their low amplitude and can only partly be displayed on the Mind Mirror screen. Sometimes they may be seen as a narrow frequency band at 38 Hz.
Brainwaves - and what they represent (part 2)
States of consciousness: a symphony of different brainwaves
The different states of consciousness can be described as combinations of beta, alpha, theta and delta brainwaves. (There is still research being done on gamma brainwaves and their significance). Most of the time we see not only one category of brainwaves but rather a combination of brainwaves interacting in concert.