Miles et al’s study of a blind man found that a man blind from birth had a circadian rhythm of 24.9 hours. He has to use stimulants and sedative to adjust his sleep/wake cycle to the standard 24 hours. This is in support of a endogenous pacemaker as the research shows that his innate biological rhythm was difficult to reset with the use of zeitgebers such as clocks and radios. These results are difficult to generalise as the man was blind so may not be applicable to those who can see and whose body clocks may have been influenced by clocks and being able to see light.
It has been claimed that the suprachiasmatic nucleus (SCN) is the dominant endogenous clock in mammals. Thus because in Morgans studies of hamsters, when the SCN was removed from the hamsters their nocturnal Circadian rhythms disappeared. But transplanting with SCN cells re-established the rhythms showing that the SCN was the main pacemaker. Ethical issues arose from this study and other like it as it use non-human animals and in other studies some animals didn’t make it through the experiment as the surgical procedure was so severe. Also you can’t extrapolate from animals to humans so it is difficult to generalise results. However the findings are supported by Stephan and Zucker’s study.
Psychologists are also interested in the effect of exogenous factors (zeitgebers). The main zeitgeber claimed to influence the body clock is light. Campbell and Murphy contribute to the theory (that light appears to be crucial in maintaining the 24 hour cycle) with an experiment in which bright light was shone onto the back of participants’ knees and the researcher were able to alter their Circadian rhythms in line with the light exposure… The exact mechanism responsible for this is uncertain. But it seems possible that the blood chemicals were altered and this was detected by the SCN.
Miles et al’s study shows importance of zeitgebers as perhaps the endogenous factors dominated because the blind individual in their study couldn’t access the key zeitgeber which is light.
Based on various pieces of research we can say our Circadian rhythms appear to be internally and externally controlled. During isolation from zeitgebers our endogenous clocks seem to be set to a 25 hour cycle, but exogenous factors such as light or social factors seem to reset our clock daily (shown in Luce and Segal’s study – those in the artic keep their clock to 24 hours by use of social communication). If control was entirely internal we would not be sensitive to external changes such as light levels and species that hibernate or migrate wouldn’t adjust their behaviour which could have severe consequences. Similarly if control was completely external our rhythms would be erratic and change day to day depending on weather conditions etc…
Generalisabilty is a huge weakness in studies into Circadian rhythms as the research includes case studies or small samples. However research into Circadian rhythms can improve our understanding of medical conditions for example: migraine sufferers perceived that they were most likely to have an attack in the morning. However evidence of migraines experienced over a year period showed that the most likely time for attack was midday.
Research into Circadian rhythms has lead great understanding for application in treating disorders and also in chronotherapeutics, the best time to take medication is a positive application of research into Circadian rhythms.
An Ultradian rhythm repeats in a cycle of less than 24 hours. An example is the sleep/wake cycle, this consists of 5 stages. Each cycle tends to last about 90 minutes. Stages 1 and 2 are called ‘light sleep’ and stages 3 and 4 are where shallow sleep becomes deep slow wave sleep. Stage 5 is rapid eye movement (REM) sleep. Stages 1- 4 are sometimes referred to as non-rapid eye movement (NREM) sleep.
Studies carried out using an electroencephalogram (EEG) showed there are different patterns of activity at different times during sleep (Rechtschaffen & Kales).
Although there is little evidence to indicate the role, if any, of endogenous or exogenous mechanisms in controlling of Ultradian rhythms Haitt and Kripke claimed this 90 minute cycle is also seen in many other basic psychological functions throughout the 24 hours such as eating and drinking.
Kleitman proposed a basic rest activity cycle (BRAC) this theory assumes that the 90 minute REM/NREM cycle that occurs during sleep continues over the 24 hours of the day and includes arousal and behavioural activity of the waking person. In general terms the REM/NREM cycle is the nocturnal fragment of a 24 hour BRAC. Support of Kleitman came from Friedman and Fischer who found 90-120 minute cycles of oral waking behaviour such as eating and drinking.
Dement and Kleitman used EEGs and were able to wake participants during each stage of sleep. They asked participants to report their feelings, experience, and emotions. They found that those awoken during REM sleep reported dreams 80-90% of the time and recalled in great detail. One strength of this research is that the results show universality as the same characteristics of sleep are shown universally. Another strength is that it has real life application; the results can be used to predict when a person is actually dreaming. However a weakness of this study is that it was carried out in a laboratory so it lacks ecological validity, on the other hand it means that extraneous variables can be controlled, and so cause and effect can be established.
Dement and Wolpert used the same technique to find that all humans dream and that people who don’t report dreams just forget them. They also found that dreams don’t last longer than 15 minutes, also eye movement during REM sleep can correspond with dream content and that content can be affected by the day’s events. One criticism is that self-report was used so reliability is decreased as participants might make things up.
Strengths of research into Ultradian rhythms are that in many of them scientific methods are used such as use of EEGs which are repeatable and reliable. Also the findings can influence theories and further experiments.
