Biological Rhythms: Ultradian Rhythms

Ultradian rhythm definition

A type of biological rhythm with a frequency of more than one cycle in 24 hours, such as the stages of sleep (the sleep cycle).

Ultradian rhythms - sleep

One of the most intensively researched ultradian rhythms is the stages of sleep. - Psychologists have identified 5 distinct stages of sleep that altogether span approximately 90 minutes - a cycle that continues throughout the course of the night. - Each of these stages is characterised by a different level of brainwave activity which can be monitored using an EEG.

Ultradian rhythms: Sleep Cycle - Stages 1 and 2

This is light sleep where a person may be easily woken. - In stage 1, the 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 pattern called sleep spindles.

Ultradian rhythms: Sleep Cycle - Stages 3 and 4

This is known as deep sleep or slow wave sleep (SWS). - The brain waves are delta waves with lower frequency and higher amplitude. - It is difficult to wake someone at this point.

Ultradian rhythms: Sleep Cycle - Stage 5 (REM sleep)

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 are most often experienced during REM sleep, but may also occur in deep sleep.

Strength

One strength of research into ultradian rhythms is that it has improved understanding of age-related changes in sleep. Sleep scientists have observed that SWS reduces with age. Growth hormone is mostly produced during SWS therefore this becomes deficient in older people. According to Eve van Cauter et al, 2000, the resulting sleep deficit may explain various impairments in old age, such as reduced alertness. In order to increase SWS, relaxation and medication may be used. This suggests that knowledge of ultradian rhythms has practical value.

weakness

One limitation of ultradian rhythms research is there is significant variation between people. Adrienne Tucker et al, 2007, found large differences between participants in terms of the duration of each sleep stage, particularly stages 3 and 4. Tucker et al suggest that these differences are likely to be biologically determined. This makes it difficult to describe 'normal sleep' in any meaningful way.

Ultradian rhythms - Evaluation: The sleep lab

One of the benefits of conducting studies of sleep in lab settings is the control of extraneous variables. This means that a researcher can exclude temporary variables such as noise or temperature that may affect sleep. However, lab studies involve being attached to complicated machinery, leading participants to sleep in a way that does not represent their ordinary sleep patterns.