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
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
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
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
Beta1 (15-18 or 16-20 Hz). An active
alert state which is associated with learning, task completion, staying
Beta2 (20-38 Hz). Intensely alert,
hyper-vigilance; highly focused state which has been correlated with