Biological Rhythms AO3 Flashcards
Circadian rhythm research evidence
The sleep-wake cycle is an example of a bodily process with a circadian rhythm. However, circadian rhythms are also influenced by EZ’s - ‘cues’ in the environment- about what time of day or night it is. In 1975 Siffre spent 6 months underground in an environment completely cut off from all EZ’s. Although he organised his time in regular patterns of sleeping and waking his body seemed to have a preference for a 25 hour rather than a 24-hour cycle. This implies that circadian rhythms are mainly controlled by EP’s rather than EZ’s.
Circadian rhythm neg- individual differences
★ However, it is important to note the differences between individuals when it comes to circadian cycles. Duffy et al. (2001) found that ‘morning people’ prefer to rise and go to bed early (about 6am and 10pm) whereas ‘evening people’ prefer to wake and go to bed later (about 10 am and 1 am). This demonstrates that there may be innate individual differences in circadian rhythms,
Circadian rhythms- determinism
★ Additionally, it has been suggested that temperature may be more important than light in determining circadian rhythms. Buhr et al. (2010) found that fluctuations in temperature set the timing of cells in the body and caused tissues and organs to become active or inactive. Buhr claimed that information about light levels is transformed into neural messages that set the body’s temperature. Body temperature fluctuates on a 24-hour circadian rhythm and even small changes in it can send a powerful signal to our body clocks. This shows that circadian rhythms are controlled and affected by several different factors, and suggests that a more holistic approach to research might be preferable.
Circadian rhythms- research evidence
Morgan (1955) bred hamsters so that they had circadian rhythms of 20 hours rather than 24. SCN neurons from these abnormal hamsters were transplanted into the brains of normal hamsters, which subsequently displayed the same abnormal circadian rhythm of 20 hours, showing that the transplanted SCN had imposed its pattern onto the hamsters. This research demonstrates the significance of the SCN and how endogenous pacemakers are important for biological circadian rhythms.
Infradian rhythms- Reinburg et al (1967) menstrual cycle
★ Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers (external factors). Reinberg (1967) examined a woman who spent three months in a cave with only a small lamp to provide light. Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days. This result suggests that the lack of light (an exogenous zeitgeber) in the cave affected her menstrual cycle, and therefore this demonstrates the effect of external factors on infradian rhythms.
Mentsrual cycle- determinism for investigating infradian rhythms
There is further evidence to suggest that exogenous zeitgebers can affect infradian rhythms. Russell et al. (1980) found that female menstrual cycles became synchronised with other females through odour exposure. In one study, sweat samples from one group of women were rubbed onto the upper lip of another group. Despite the fact that the two groups were separate, their menstrual cycles synchronised. 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. These 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.
Evaluation for ultradian rhythms
★ Demont and Kleitman (1957) used an EEG to investigate brain activity during sleep over the course of a night. 9 participants who had not drunk caffeine or alcohol slept in a sleep lab and were tested with the EEG. They were woken at different points. If woken during REM sleep they would report dreams. This helped psychologists understand what occurs during REM sleep.
★ Individual Differences: The problem with studying sleep cycles is the differences observed in people, which make investigating patterns difficult. Tucker et al. (2007)
found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4 (just before REM sleep). This demonstrates that there may be innate individual differences in ultradian rhythms, which means that it is worth focusing on these differences during investigations into sleep cycles.
★ In addition, this study was carried out in a controlled lab setting, which meant that the differences in the sleep patterns could not be attributed to situational factors, but only to biological differences between participants. While this study provide convincing support for the role of innate biological factors and ultradian rhythms, psychologists should examine other situational factors that may also play a role.
★ Additionally, the way in which such research is conducted may tell us little about ultradian rhythms in humans. When investigating sleep patterns, participants must be subjected to a specific level of control and be attached to monitors that measure such rhythms. This may be invasive for the participant, leading them to sleep in a way that does not represent their ordinary sleep cycle. This makes investigating ultradian rhythms, such as the sleep cycle, extremely difficult as their lack of ecological validity could lead to false conclusions being drawn.
★ An interesting case study indicates the flexibility of ultradian rhythms. In 1964 Randy Gardener remained awake for 264 hours. While he experienced numerous problems such as blurred vision and disorganised speech, he coped rather well with the massive sleep loss. After this experience, Randy slept for just 15 hours and over several nights he recovered only 25% of his lost sleep. Interestingly, he recovered 70% of Stage 4 sleep, 50% of his REM sleep, and very little of the other stages. These results highlight the large degree of flexibility in terms of the different stages within the sleep cycle and the variable nature of this ultradian rhythm.
