The on-going electrical activity of the brain (EEG) measured from electrodes placed on the scalp is an example of a stochastic signal which may give some information about the general mental state of the individual.

Alpha waves are 7.5 Hz to 13 Hz relatively large amplitude (usually less than 50 microV, although this can be variable from subject to subject). EEG waves are associated with a relaxed but awaken state. They are usually best seen in the posterior regions of the head on each side, being higher in amplitude on the dominant side.