EEG Brainwaves Frequency Bands
(below 4 Hz) are the slowest, highest amplitude brainwaves, and are what is experienced while asleep. Rhythmic delta activity (sinusoidal) is usually considered pathological during the waking state, whereas, asymmetrical mixed frequency delta (1 – 4 Hz) often occurs during complex processing and may represent linkage of the higher frequency, local processing in beta from different cortical regions.
(4 – 8 Hz) occur at two levels. The lower range of theta (4 – 6 Hz) basically represents the twilight zone between waking and sleep. It is a profoundly calm, serene state. In this range, conscious intellectual activity is not occurring. By contrast, the higher range of theta (6 – 8 Hz), when it is frontal-midline, seems to be where the mind goes when engaging in complex, focused problem solving, such as mental arithmetic.
(8 – 12 Hz) are lower frequency (slower) and higher amplitude. They are associated with a state of relaxation and basically represent the brain shifting into idling gear, relaxed and disengaged, waiting to respond when needed. Alpha is also associated with complex tasks that have been mastered to the point where they can be performed automatically. If one closes the eyes and begins picturing something peaceful, in less than half a minute there begins to be an increase in Alpha brainwaves.
(above 12 Hz) are higher frequency (faster), low amplitude brainwaves associated with a state of mental, intellectual activity and outwardly focused attention or concentration. It is an active processing state.