Biological Rhythms

Infradian and Circadian rhythms - everything you need to know for the AQA Unit 4 psych module

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Biological Rhythms
Infradian Rhythm ­ a rhythm lasting more than 24hrs
Circadian Rhythm ­ a rhythm lasting 24hrs
Ultradian rhythm ­ a rhythm lasting less than 24 hrs
Circadian Rhythm: the sleepwake cycle
The suprachiasmitic nucleus (SCN) is in the hypothalamus, just above the optic chasm so it can gain input fairly directly from
the eyes.
Morgan (1995)
Removed SCNs from hamsters, circadian rhythms disappeared.
Transplanted SCNs from hamsters who had mutant circadian rhythms, found the hamsters receiving transplants took on the
mutant rhythm.
Silver et al (1996) if SCNs are transplanted into an animal whose SCN is removed, the animals receiving the transplants have
restored rhythms.
SCN is endogenous pacemaker
Ethics: PfH humans and hamsters have same SCN? Human SCN maybe more complicated hard to gen.
Findings show a consistent effect removing and transplanting SCN: highly skilled neurosurgeon ­ hard to replicate/
test. Lab ­ controlled, C&E.
Schochat et al (1997) Role of melotonin in circadian rhythms. 6 males spent 29 consecutive hours in a sleep lab. Spent 7 mins
in every 20 lying down in a dark room trying to sleep. Blood samples taken every 20 mins to measure melotonin. A daily
secretion of melotonin into the blood consistently preceded sleepgate by 100120 mins. Insomniacs find it easier to sleep
when given melotonin 2 hours prior to sleep.
Melotonin is usually an endogenous pacemaker, but is a zeitgeber 2.
Sleep lab, specialist artificial environment/ informed consent/ PfH ­ stressful/ androcentric and small sample.
Study is biological, can generalise. Does not say melotonin causes sleep, just that it precedes it.
Helpful for insomniacs. The drug proves more likely that melotonin does cause sleep.
Michel Suffre: spent 2 months living in a dark cave, developed a 25 hour sleepwake cycle.
a pattern exists ­ biological clock?/ Natural light is the big exogenous zeitgeber and is necessary for 24hr cycle/ as a
case study, can't establish why this occurred or C&E/ individual differences.
Miles et al (1977) a man blind from birth. 24.9 circadian rhythm despite his alarm clocks. Only way to reset rhythm to 24 hrs
was to use sedatives to help him sleep and stimulants to help him wake. This suggests light is v. important to keep 24hr
Luce and Segal (1966) Arctic circle people sleep for 7hrsin summer despite sun at night.
shows that main E.Z. not always needed some instances other zeitgebers (such as social customs) take over.
Overall A02:
E.Z. keep us in a synchronised cycle to maintain order. Nothing would function if we relied solely on E.P.
Infradian Rhythm: the menstrual cycle
The endogenous pacemakers are hormones: oestrogen and progesterone.
Reinburg (1967)
Women who lived in cave for 3 months with dim lighting: cycle shortened and sleepwake cycle lengthened.
Light acts as an exogenous zeitgeber for the menstrual cycle
Can't generalise because study was on 1 woman ­ indiv. Diff. Artificial environment could change cycle.
Strange results, no men so cycle should have been longer or stop ­ no chance of pregnancy.
Women who spend time together have synchronised cycles, possibly because of pheromones.
Women who work with men often have shorter cycles because of pheromones released by men.
Pheromones are exogenous zeitgebers
Makes evolutionary sense for pheromones to shorten cycle of women if they work with men because there's more time
to get pregnant. Do all men have this feature? (e.g. boys before puberty? old men? Etc)
Russell et al (1980)
Control group and experimental group. Donor's odour was collected from pads under arms dissolved in alcohol to rid bacteria
placed on upper lip of Pp. After 5 months: 4/5 exp. Group had synchronised cycles.
More reliable study as: collected pheromones in a valid way, highly controlled study (C&E), had control group
Can generalise because its biological (cultures don't matter) BUT some women might emit stronger/ more pheromones
than others
Not all women affected: hormones more influential than Pher/ Pher more likely to coincide with similar cycle.

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Evolutionary reason: Women's menstrual cycles coincide so women have babies at same time so mothers can care
for all babies…read more



Thank you! This is really useful! 

It's in note form and lists lots of really useful AO2 points :)

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