Describe and evaluate research on ultradian and infradian rhythms.

of sleep and the fifth is REM sleep. S One sleep cycle goes through 5 stages of sleep which lasts around 90 minutes. Stage 1 and 2 sleep stages are light sleep characterised by Alpha and Theta brain waves heart rate slows and temperature drops. Stage 3 and 4 sleep are characterised by Slow Wave Sleep (SWS) in this state it is harder to wake someone up, delta brain waves are produced , metabolic rate slows and growth hormone is produced. In stage 5 REM sleep is called ‘paradoxical sleep’ because brain and eyes are active but the body is paralysed. One issue with REM sleep is the assumption that it is dreaming sleep. This is supported by research Dement and Kleitman (1957), were first to demonstrate this link they woke participants up during REM and found high levels of dreaming, however they also found that pp’s were dreaming in NREM sleep. Also when awoke they were not always dreaming. This is important of the REM/dream link as it potentially provides a way to identity when someone is dreaming and therefore might provide theorist with a way to explain dreaming – for example Hobson and McCarley (1977) proposed that dreams are just a psychological read-out of the random electrical signals typical of REM sleep. However such theories are based on the erroneous assumptions that REM activity equals to dreaming.         Basic rest-activity cycle, the 90 minute sleep stage cycle is itself located within a 24-hour circadian rhythm, so it would make sense that this 90 minute ‘clock’ is running through-out the day. This is called basic rest-activity cycle (BRAC) Friedman and Fisher (1967) observed eating and drinking behaviour in a group of psychiatric patients over a period of 6 hours. The detected a clear 90 minute cycle in eating and drinking behaviour. This would make sense as it would ensure all biological processes run in unison. There have been other people to research into BRAC that have supported Friedman and Fishers findings.         Infradian Rhythms are such as the female menstrual cycle. These are driven by fluctuations in hormone levels. The fluctuation of the menstrual cycle is to regulate ovulation. The pituitary gland releases hormones FSH and LH