The brain functions by sending electrical signals from one place to another. Very small charges pass between nerve cells, accompanied by changes in electrical potential, in voltage.
This activity can be measured and displayed as a wave form called brain wave or brain rhythm. The height of the wave is a measure of the potential difference, its frequency is a measure of the rate at which electrical charges pass through a nerve cell or nerve fibre.
A person's brain is active all the time, waking and sleeping, producing and shifting between distinct wave forms which are commonly grouped as follows:
Table 1
Brain Waves
| Frequency band (cycles/second) | Name of Wave Band | Description |
| 1 - 3 | Delta | Generally strongest when a person is in a deep dreamless sleep. |
| 4 - 7 | Theta | May be associated with dreamy, creative, intuitive states. |
| 8 - 10 | Alpha | Associated with a calm and relaxed state when the person is not thinking. |
| 15 - 30 | Beta | Associated with being alert, with normal thinking, with processing information. |
When delta waves predominate then one is said to be in a delta state.
People can think of relaxing and so strengthen alpha waves, or can do mental arithmetic and so weaken them. This enables people 'to perform an on-off decision, switching a light on or off or moving a cursor on a screen'.
