The 4-5 cycles per second rhythm--changes in time.

The 4-5 cycles per second (c/s) rhythm is a relatively rare, individual EEG variant. Age distribution of subjects carrying this variant and longitudinal studies over many years have indicated that it may sometimes disappear during middle age. Observations on female monozygotic twins at 15, 23 and 45 years of age suggest that disappearance of this trait might also be under genetic control.