This section aims to give a brief description of main EEG signals recorded at the scalp surface. This list is not exhaustive at all. For more details, you can consult wikipedia page on EEG and soon my phD thesis.
The alpha rhythm
The alpha rhythm is a signal between 8 and 13 Hz mainly located on occipital area (back of the head).
It appear only when the eyes are closed.
It tends to disapear for old people
The mu rhythm
The mu rhythm is a signal from 8 to 10 Hz mainly located on central and temporal area (plan going through the two hears and the top of the bone).
It disappears as soon as the patient move or imagine a movement.
The main visible rhythm correspond to motor area of hands and it can be seen mainly on electrode C3 and C4 (The left hemisphere controls the right hand and reciprocally).
This rhythm come with a beta rhythm (> 13 Hz) but it is not visible on EEG surface.
The slow waves
On adult subject, slow waves are often epilepsy symptom.
There exist two kind :
- The delta waves between 0 and 4Hz.
- The theta waves between 4 and 8Hz.
Their location often reveal the center of epileptic source.
The paroxysms
Paroxysms are epilepsy symptoms
They often have high amplitude (> 0,5 mV) and can have various shape. One of the most common is the spike wave (spike followed by a slow wave) like above illustrated.
