Lesson 7 Flashcards
what are biological rhythms?
distinct patterns of changes in body activity that conform to cyclical time periods. Biological rhythms are influenced by internal body clocks (endogenous pacemakers) as well as external changes to the environment (exogenous zeitgebers).
the sleep - wake cycle
- dictates when humans and animals should be asleep and awake.
- lightness and darkness are external cues which determine when we sleep and wake up.
- governed by an internal body clock (endogenous pacemaker) called the SCN (suprachiasmatic nucleus) which is located on the hypothalamus.
- it receives info about light and the exogenous zeitgebers can reset the SCN.
What is Siffre’s cave study
aim- to investigate the influence of the absence of external cues on circadian rhythms.
procedure - Siffre subjected himself to long periods of time living underground without any external cues e.g. light to guide his rhythms. he woke up ate and slept and slept when he felt it was appropriate to do so. the only thing influencing his behaviour was his internal body clock free running circadian rhythms.
after his first underground stay of 61 days in the southern alps in 1962, he surfaced in mid september, however he believed it to be mid august.
siffre’s cave study
his biological rhythms were 25 hrs, longer than the expected 24 hrs but he did continue to fall asleep and wake up on a regular schedule, so he did maintain a regular sleep - wake pattern.
this suggests the biological clock ran at a natural rate and circadian rhythms persist despite the absence of exogenous zeitgebers, however we need entrainment from exogenous zeitgebers in order to keep to a 24 hr cycle.
other evidence?
- a group of ppt spent 4 weeks in a WW2 bunker, where they had no natural light.
- all but one of the ppt displayed similar results to that of Siffre they had a circadian rhythm of over 24hrs.
conclusion
this helps conclude our natural sleep/wake is entrained by exogenous zeitgebers associated with our 24 - hour day.
However, folkard et al
this study suggests that the influence of environmental cues should not be overestimated.
12 people agreed to stay in a cave across a 3 - week period, going to bed at a set time (shown by a clock) and waking up a set time (shown by a clock).
as the study went on, the researchers sped up he clock, so that the ‘day’ lasted for only 22hrs.
the results found only one of the ppts were able to adjust this.
conclusion
this suggests the free - running biological clock can override some external changes in the environment.
other circadian rhythms
- core body temp is an indicator of the circadian rhythms.
- it is at its lowest (36 degrees) at 4:30am and highest (38 degrees) around 6pm.
- this can affect our mental abilities - the warmer we are internally, the better our cognitive performance.
- sleep typically occurs when the core temperature starts to drop, and the body temperature starts to rise towards the end of a sleep cycle promoting feelings of alertness first thing in the morning.
- Gupta (1991) found improved performance an IQ tests when assessed at 7pm as opposed to 2pm and 9am.
practical application to shift work
a strength of circadian rhythms that it provides an understanding of the adverse consequences that occur when they are disrupted (desynchronization).
for example, research has found night workers engaged in shift work experience a period of reduced concentration around 6am, meaning mistakes and accidents are more likely to happen and shift workers are also three times more likely to suffer from heart disease as a result of stress from adjusting to sleep/wake cycle.
this informs employers regarding their working hours and what will be more efficient for their workplace, along with how to minimise and prevent harm to their employees.
therefore this suggests understanding of circadian rhythms can maintain worker productivity and preventing accidents in the workplace.
medical treatment
strength of our understanding of circadian rhythms is the practical application to drug treatments.
aspirin as a treatment for heart attacks is most effective when taken last thing at night. Aspirin reduces blood platelet activity and this can reduce the risk of heart attack which are most likely to occur early in the morning, so the timing of aspirin is vital.
by understanding circadian rhythms and their impact on health, it can help determine the best time to administer drug treatments as research has suggested there are peak times during the day or night when drugs are likely to be the most effective.
therefore the concept of circadian rhythms has high external validity.
poor control in studies
limitation of the research into circadian rhythms is the use of small samples and individual differences.
For example, in Siffre’s study there was only one individual and the Folklard, Wever and Aschoff study were conducted on a handful of people. Additionally, Siffre observed when he had his most recent cave experience in 1999 at the age of 60, his internal biological clock ticked much more slowly compared to when he was a young man, his body followed more of a 48 hour cycle.
it is impossible to generalise these results to the whole population of people and there may be some individual differences like age/ gender could have significant impact on our circadian rhythms.
therefore, research into circadian rhythms lacks population validity and prevents general conclusions to be drawn.
