"At low brain activity, large groups of nerve cells discharge simultaneously, and this synchrony is displayed in the EEG as low frequency waves and large amplitude as "slow waves": 1) alpha waves with frequencies ranging from 8 to 12 cycles per second (8-12 Hz), they are characteristic of a relaxed body when a person sits comfortably with the Gauls closed; 2) theta waves with frequencies ranging from 4 to 7 Hz, they appear in the first stage of sleep; 3) delta waves (0.5-3 Hz), which are recorded during deep sleep. During brain activity, each participating nerve cell discharges with its own specific function in its own rhythm; as a result, brain activity becomes asynchronous and is recorded as fast waves of high frequency and small amplitude – "beta waves" (13-26 Hz); the amplitude of beta waves decreases as brain activity increases. Beta waves are recorded during waking, active mental and physical activity, and, oddly enough, during "fast sleep".