Body rhythms are periodically repeated patterns which occur within the body and are governed by internal factors known as endogenous pacemakers, such as hormones and external factors known as exogenous ‘zeitgebers’ (time-givers), such as light and dark. The three main classifications of body rhythms are: Circadian is a twenty-four hour cycle, for example sleep and wakefulness, Ultradian is less than the twenty-four hour cycle, for example sleep stages and Infradian which is longer than the twenty-four hour cycle, for example the menstrual cycle.
Over the years there have been numerous experiments to establish the causes of body rhythms and the effects of altering them. One theory which inspired such research was based on the suprachiasmatic nuclei (SCN), which are the neurons situated in the hypothalamus. The SCN, in conjunction with the pineal gland, were predicted to be factors determining the regulation of the circadian rhythm. It has since been proved that zeitgebers, such as light and dark, are received via the retina triggering SCN activity. The SCN subsequently generates the secretion of the hormone melatonin from the Pineal Gland, which ultimately produces another hormone called serotonin which modulates sleep patterns.
This theory was researched by Michel Siffre (1972) who carried out an experiment known as ‘The Cave Study’, in which he withdrew all zeitgebers and relied solely on his endogenous pacemaker (internal body clock). Siffre remained in a cave for over six months without any natural light, sounds or any other time determining cues. His behaviour patterns were monitored by a camera installed in the cave, he wore wires to record his physiological functions and he was able to speak to researchers by telephone. He was guided by his bodily intuition as to when he should sleep or wake. Initially his behaviour patterns were irregular but eventually they settled down and his circadian cycle stabilised at around 25 hours.
The experiment demonstrated that, it is due to the zeitgebers that our bio rhythms are synchronised with the twenty-four hour clock. Consequently, if they become damaged or tampered with, it is possible that the circadian rhythm may disappear altogether. However, because the experiment was undertaken in unnatural settings it would be considered a laboratory experiment and it could therefore be disputed that the setting could have affected his behavioural patterns, resulting in the experiment being considered low in ecological validity. Additionally, there were no confounding variables, which would naturally occur in the ‘real world’. The ‘sample’ also had low validity because it was self-selecting, did not have any variables, was based on only one individual and was not repeated to substantiate the conclusions. Demand characteristics could also be argued, as Siffre had predetermined expectations of what would happen to his behavioural patterns.
Another argument could be that the experiment was carried out on humans only and therefore would the same results occur in other animals. This was resolved by undertaking a similar experiment on rats in which the SCN was removed from the rat altogether. The findings illustrated that the rats circadian rhythm disappeared altogether, adding weight to Siffre’s theory.