Biological Rhythms: Infradian and Ultradian Rhythms

• Infradian Rhythm = frequency of one complete cycle occurring less than once every 24 hours. Such rhythms are entrained by endogenous pacemakers and exogenous zeitgebers. Examples of infradian rhythms include the menstrual cycle
• russel et al (1980) showed menstrual cycle synching amongst 29 women who all had irregular periods. The pheromones from 9 of the women were collected through the use of a pad under the armpit, and then rubbed onto the upper lip of the remaining 20 women, found that female menstrual cycles became synchronised with other females through odour exposure. This suggests that the synchronisation of menstrual cycles can be affected by pheromones, which have an effect on people nearby rather than on the person producing them.
• Seasonal affective disorder is an example of the influence of endogenous pacemakers on the circadian sleep-wake cycle. SAD is an infradian disorder caused by disruption to the sleep-wake cycle, and commonly occurs in the winter. Longer nights means that more melatonin is secreted from the pituitary gland which changes the production of melatonin, leading to feelings of loneliness and depression.
• Ultradian Rhythm = One of 3 types of biological rhythms, with a frequency of one complete cycle occurring more than once every 24 hours. A notable example are the stages of sleep, where a full sleep cycle takes 90 minutes to complete.
• Stages 1 and 2 represent the ‘sleep escalator’ where the participant can easily be awoken, stages 3 and 4 coincide with deeper and slower delta waves , whilst stage 5 represents REM sleep. REM sleep is closely associated with dreaming and characterised by movement inhibition and a sensory blockade. The stages of sleep have been demonstrated by Dement and Kleitman.
• Dement and Kleitman (1957) studied 33 adults, where their caffeine and alcohol intake had been controlled, in order to remove the effect of these extraneous variables and increase the reliability of the findings.
• Using EEG scans, the researchers found that “ separate periods of rapid eye movement potentials were recorded without exception during each of 126 nights of undisturbed sleep”. Since participants were able to accurately recall their dreams when awoken during REM sleep, the assumption was made that dreaming is associated with REM sleep. Therefore, there is clear evidence supporting the idea of a distinct set of sleep stages.
• Menstrual synchronisation is not always present in all-female samples = there are external (extraneous) variables which may affect the timing and duration of their menstrual cycles. McClintock et al. did not control for such extraneous factors e.g. smoking, physical activity and alcohol consumption. Therefore, this raises doubts about the strength of the influence of pheromones, as an exogenous zeitgeber which can entrain infradian rhythms.
• russel's findings indicate that external factors must be taken into consideration when investigating infradian rhythms and that perhaps a more holistic approach should be taken, as opposed to a reductionist approach that considers only endogenous influences.