Biorhythms - Circadian Rhythm

Frage	Antworten
How long does a Circadian Rhythm last for?	About 24 hours
Give an example of a circadian rhythm	Sleep-Wake cycle
Define 'Endogenous Pacemaker'	Internal body clocks that regulate biological rhythms
What are examples of endogenous pacemakers?	Supercharismatic Nucleus (SCN) and the Pineal Gland
What is a characteristic of endogenous pacemakers?	They are free-running (work without external cues)
Define 'Exogenous Zeitgebers'	External environmental factors that have an effect on our endogenous pacemakers
What are examples of exogenous zeitgebers?	light, temperature, social cues
Explain the Sleep-wake cycle, keeping in mind exogenous zeitgebers and what they do.	We sleep when it is dark and awake when it is light. The amount of light cues sleep-wake cycle
Does the sleep-wake cycle work without external cues?	Yes, it is free-running, setting a cycle of about 24-25 hours
Is the sleep-wake cycle accurate without natural light?	Although the sleep-wake cycle does persist in the absence of natural light it is NOT 100% accurate.
Is there support for the sleep-wake cycle being 'free-running'? If so, what?	Yes, Michel Siffre lived underground with no external cues (light, clock etc.) in order to study his biorhythms. He slept, woke and ate when he felt like it and only influence on his behaviour is his internal clock.
What did they find?	He emerged after having spent 61 days underground on 17th September thinking it was August 20th. His day had lengthened to up to 32 hours long.
Is there support for Siffre?	Yes, Aschoff and Wever (1976) placed participants underground in WWII bunker with no environmental/social cues. Their rhythms were set at 24-25 hours although some were increasing to 29.
Is there a validity issue with Siffre's research? If so what is it?	Siffre's study may be classed as a case study as it is a study on one individual and therefore would have unique features. His body's behaviour may not represent all people as we are all different and also living in a cave may have it's own effects.
Does Siffre's study have ecological validity?	Siffre's study lacks ecological validity as living in a cave isn't something we would experience in every day life.
Is there a limitation for research into the sleep-wake cycle?	Yes. Czeisler et al (1999). In all studies the participants were isolated from clocks, radios, daylight etc. but not artificial light as it was thought that dim light in contrast to daylight would not effect rhythm. This is NOT TRUE, altered participants rhythms to 22 and 29 hours using just dim lighting.
What are the two types of individual differences?	1. cycle length Czeisler et al (1999) found that circadian cycles in different people can vary from 13-65 hours 2. When Circadian Rhythms reach their peak Duffy et al (2000) morning people rise early and sleep early (6am-10pm); evening people rise later and sleep later (10am-1am)
Is there support for the importance of external cues?	Yes. Folkard et al (1985)
What did Folkard et al (1985) wonder?	Whether external cues could override the internal clock
What experiment did Folkard et al (1985) do?	12 participants stayed in a cave for 3 weeks with no natural light or time cues. They were told to sleep when clock says 11:45pm and wake when it says 7:45am. Initially clock ran normally but they sped it up making the participants think 24 hours had passed when actually only 22 had. At first their circadian cycle matched the clock but as it quickened their cycle ceased to match it and instead followed 24 hours (not 22 imposed by the experiment) (except 1 participant did adapt to 22)
What do the findings suggest?	Our circadian rhythm can only be guided by external factors to a limited extent.
What is an interesting feature of these experiments?	As soon as the experiment ended the participants took only a few days to resynchronise to their cycles to the available external time cues (i.e. clocks and daylight) showing the influence of such external cues.
What is another example of a circadian rhythm?	Core body temperature
Explain core body temperature as a circadian rhythm	Core body temperature is the best indicator. Lowest at 4:30pm (36 degrees) and highest at 6pm (38 degrees). There is a slight dip after lunch regardless of food intake, afternoon siesta related to this - example of ultradian rhythm as it happens bi-daily.
What are the effects of core body temperature changes?	Core body temperature is linked to cognitive abilities
What study was conducted to investigate the effects of core body temperature on cognitive ability?	Folkard et al (1977) had stories read at either 9am or 3pm to children ages 12-13. After one week the afternoon group (Higher Core body temperature) had superior recall and comprehension, retaining 8% more meaningful material.
What did this study by Folkard conclude about the effects of core body temperature on cognitive ability?	This study concluded that long term recall is best when core body temperature is higher.
Who else tested the effects of core body temperature on cognitive ability and what did they find?	Gupta (1991) found that performance on IQ tests were best at 7pm as opposed to 9am or 2pm.
Is there more evidence that core body temperature effects cognitive ability?	Yes, Giesbrecht et al (1993) lowered the body temperature of participants by placing them in cold water, their cognitive performance was worse on some tasks.
Is there conflicting evidence as to whether body temperature effects cognitive ability?	Some people claim the link is spurious. Hord and Thompson (1983) tested cognitive performance in the field as opposed to a lab situation and found no correlation.
What could be an explanation for improved cognitive ability with high core body temperature?	Wright et al (2002) suggested that high core body temperature leads to increased physiological arousal and this leads to improved cognitive performance
Name a third circadian rhythm	Hormone production
explain hormone production as a circadian rhythm	Cortisol is at it's lowest around midnight and peaks around 6am.
When is cortisol produced?	cortisol is produced when we are stressed but is also related to making us alert when we wake up and explains why if we awaken at 4am it is hard to think clearly. It is because cortisol levels are not sufficiently high for alertness.
Which two other hormones have a clear circadian rhythm?	melatonin (which induces sleepiness) and growth hormone.
The explanations for the circadian rhythms suggest that the sleep-wake pattern is fixed (determined) by internal mechanisms. Who demonstrates the power of these biologically determined rhythms?	A man who is blind exposed himself to external factors such as clocks etc. and none had an effect on his rhythm. Light did not reset his circadian rhythm. This meant that it was difficult for him to function in a world tuned into cues such as clocks and daylight (Miles et al 1977)
How may this deterministic view be somewhat misleading?	It is clear that the internal mechanism is powerful but there is some flexibility in this system. For example we can decide to go to bed 2 hours later and wake up at the same time the next day, without too much difficulty.
What did Folkard's study show?	One person managed to keep to the 22 hour rhythm which shows that other factors can override the internal clock.
Is there a Real World Application from research into circadian rhythms?	Chronotheraputics. Since the circadian rhythm affects digestion, heart rate, hormone secretions and other functions, this should be taken into account when taking drugs.
What is Chronotheraputics?	the study of how timing (chronos) affects drug treatments (therapy)
How does research into circadian rhythms help us to understand when medications should be taken?	Medications that act on certain hormones may have no effect if taken when target hormone levels are low, but are fully effective if taken when levels are high. Another example is taking aspirin to treat heart attacks (which normally occur early in the morning). This is most effective at around 11pm which allows the aspirin to peak in the blood stream (takes 2-4 hours).
What is a second real world application?	This research helps us to know that it is best to study in the morning and early evening when we are most alert.

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