Biorhythms and Aggression
By Catherine Walker
Topic I: Bio-rhythms (separated into six essay topics)
Biological rhythms: There are three types of biological rhythm; circadian, ultradian and infradian. Circadian rhythms are those which complete a cycle in a 24 hour period such as the sleep-wake cycle, heart rate or metabolism. People have variations within the circadian rhythms, notably the owl/lark division describing people who have biological clocks which run ahead or behind the average. Ultradian rhythms are those which occur more than once in a 24 hour period, for example eating or the sleep cycle which repeats approximately four times per night. Infradian rhythms are those which occur over a period greater than 24 hours, such as the menstrual cycle and PMS. These and SAD (seasonal affective disorder) are the infradian rhythms which have attracted the most psychological research.
The stages of sleep are an example of an ultradian rhythm, repeating roughly every 90 minutes while asleep. Since the invention of the EEG in the 1930’s the research into stages of sleep has drastically increased. In 1968, Kales and Rechtschaffen discovered four distinct stages people entered during sleep. Stage 1 usually lasts for roughly 15 minutes at the beginning of the cycle and is characterised by slower ‘theta’ brain waves. Stage 2, lasting about 20 minutes is characterised by sleep spindles (bursts of high cognitive activity) and K-complexes. Following this is stage 3, which lasts for 15 minutes. In this stage, brain waves slow and increase in amplitude and wavelength, developing into delta waves. Stage 4 is similar to stage 3 and is when a person is most relaxed and most difficult to wake. The fifth stage of sleep is called REM (as opposed to stage 1-4 which are NREM stages). During REM sleep the brain is almost as active as it is during the day. Sleep paralysis also