The EEG is a measure of voltage as a function of time. The voltage of the EEG
regulates its amplitude (measured from peak to peak). EEG amplitudes in the cortex
range start from 500 to 1500 lV, but the amplitudes of the scalp EEG range
between 10 and 100 lV [1, pp. 11–12]. The attenuation is due to the deprived
electrical conductivity of brain muscles, skull then scalp. In common, EEG signals
signify the mixture of waveforms, and remain usually classified according to their:
(a) Frequency (speed);
(b) Amplitude (power);
(c) Wave morphology (shape);
(d) Spatial distribution (topography);
(e) Reactivity (behavioural state).