Typically, EEGs are divided into the following frequency bands: delta (1–3 Hz), theta (3.5–7.5 Hz), alpha (8.0–11.5 Hz), beta (12–28 Hz), and gamma (28.5–50.0 Hz), with each frequency reflecting a different degree of brain activity. In healthy adults, medium (8–13 Hz) and fast (14–30 Hz) frequencies are predominant in the awake resting EEG, with only sparse occurrence of low frequencies (0.3–7.0 Hz) and high frequencies (greater than 30 Hz). The resting EEG is stable throughout healthy adult life and is highly heritable (van Beijsterveldt et al. 1996).
