biological rhythms: ultradian rhythms

• sleep pattern occurs in 90 minute periods and keeps repeating itself. Sleep is divided into 5 stages, each characterised by a different level of brainwave activity monitored using EEG. Sleep is an example of an ultradian rhythm
• stage 1 + 2 of sleep cycle: this is light sleep where a person may be easily woken. In stage 1, brain waves are high frequency and have a short amplitude. These are alpha waves. In stage 2, the alpha waves continue but there are occasional random changes in the pattern called sleep spindles
• Stage 3 + 4 of sleep cycle: this is known as deep sleep or slow wave sleep. The individual waves now have lower frequency and higher amplitude. It is difficult to wake someone at this point
• Stage 5 of sleep cycle: the body is paralysed yet brain activity closely resembles that of the awake brain. During this time, the brain produces theta waves and the eyes occasionally move around, thus rapid eye movement (REM). Dreams most often experienced during REM sleep, but may also occur in deep sleep
• One strength of ultradian rhythms is understanding age related changes in sleep. Slow wave sleep reduces with age. Growth hormone is produced during slow wave sleep so this becomes deficient in older people. Researchers suggests the reduced sleep may explain impairments in old age. Slow wave sleep can be improved using relaxation and medication. This suggests that knowledge of ultradian rhythms has practical value