AO3 Biological rhythms: circadian, infradian and ultradian and the difference between these rhythms. The effect of endogenous pacemakers and exogenous zeitgebers on the sleep/wake cycle.

Data collected in Siffre’s study into circadian rhythms

The data collected about the times of sleeping and waking up is reasonably objective so is easy to check.

Generalisability to Siffre’s study into circadian rhythms

It is a case study to generalisation to other people is unsafe, however other research shows similar findings. But Siffre replicated this study at a older age and found his internal clock ticked much slower than when he was younger, showing the results cannot be applied to all age groups.

Showing the role of exogenous zeitgebers and endogenous pacemakers in Siffre’s study

As the sleep/wake cycle was developed without exogenous zeitgebers it suggests there are internal processes governing the sleep/wake cycle. The findings suggest our internal clock must have a 25 hour cycle and the zeitgebers must reset the clock to the usual 24 hour cycle

Morgan’s invaluable evidence from animal studies

The study has provided invaluable evidence to suggest that the SCN is the biological clock which controls the sleep/wake cycle. This is supported by the carefully controlled scientific procedures used which have also been replicated many times.

Generalisability of Morgan’s animal study findings

Many critics of animal studies argue it’s not possible to generalise from animals to humans. However, this research focuses on the most primitive of brain structures and although our cortex can modify its effects, we are still slaves to our hypothalamus.

Effects of damage or trauma during Morgan’s animal study

Some argue there is the possibility that the observed effects of removing the SCN could partly be due to the trauma of surgery or damage toother areas of the brain. However, the fact that a normal circadian rhythm can be re-established with transplanted foetal tissue tends to discredit this view.

Ethical concerns of Morgan’s animal study

This research is pursued because of the possible benefits from humans, so some questions whether it’s right to subject one species to painful procedures for the benefit of humans. However some argue that if it leads to the relief of human suffering then it would be unethical not to carry it out.

Morgan’s research shows the role of endogenous pacemakers

This research suggests the SCN is a vital endogenous pacemaker, responsible for controlling circadian rhythms

Practical application of research into circadian rhythms on chronotherapeutis

This is the study of how timing affects drug treatments. It has shown that taking aspirin to avoid heart attacks is most effective at around 11pm as heart attacks normally occur in the morning.

Practical application of research into circadian rhythms on shift work

Czeisler and Coleman studied workers in a chemical plant in Utah, where shift patterns went from day-night-evening changing each week. But staff had many health problems, sleep difficulties and work-related stress. So instead a pattern of day-evening-night in a 3 week rotation improved job satisfaction, increased productivity and reduced time off sick.

Investigation of pheromones in McClintock’s study

The results suggested that pheromones are important in regulating the menstrual cycle, therefore exogenous factors play a role as well as endogenous ones. However, pheromones weren’t directly investigated in this study.

Cause and effect relationship in Russel’s study

It uses an experimental design with high levels of control over potentially confounding variables such as sexual activity and awareness of which group they were in or the menstrual cycle of the donor. This means that a causal relationship can be established, and we can say with some conviction that the presence of the odour caused the synchrony in the menstrual cycle.

Sample size in Russell’s study

The sample size was extremely small which makes it difficult to generalise beyond the study, and it offers no explanation for why one person didn’t respond to the donor’s odour.

Russe