What is EEG?

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EEG is a physiological indicator of brain activity and is a non-invasive recording of the activity of the brain at different locations on the outside surface of the scalp using electrodes. An EEG machine is essentially a piece of equipment which monitors the electrical activity generated by brain cells, also known as neurons.

When a neuron "fires", a change happens in the electrical field within and around the neuron. By placing electrodes on the scalp, the changes in the electrical fields generated by many neurons can be detected and amplified. By using an EEG machine, the frequency and patterns of neuronal activity of the cortex can thereby be assessed. Quantitative EEG (qEEG) is the term used to describe recording and analyses of EEG from a multitude of scalp sites during rest and different mental tasks.

To facilitate the recording of EEG activity from many sites, the client wears a cap as shown in the picture above, which has electrodes built into it.

Traditionally, EEG is defined by 4 frequency bands:

These 4 frequencies are sometimes subdivided into smaller frequency bands which are associated with specific psychological states.


Delta (0.5-3.0 or 0-4 Hz). These are primarily found during deep sleep but if found when awake may be indicative of an underlying lesion.

Theta (3-7 or 4-8 Hz). These waveforms are observed during hypnagogic states (waking up/falling asleep) and are normally indicative of low levels of alertness. However, research has shown that they are also important to memory consolidation. Predominance of this waveform is associated with thinking which is image-based and creative-intuitive.


Alpha (8-11 or 8-12 Hz). When an individual is at rest or relaxed, “alpha waves” around 10 Hz are generated, which disappear when the individual becomes alert. Traditionally, alpha is associated with pure awareness without processing.

SMR/LoBeta (12-15 or 12-16 Hz). Increased SMR activity is observed during physical stillness and is associated with body presence. People often report feeling heavy and warm.


Beta1 (15-18 or 16-20 Hz). An active alert state which is associated with learning, task completion, staying focused.

Beta2 (20-38 Hz). Intensely alert, hyper-vigilance; highly focused state which has been correlated with anxious rumination.

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