Circadian rhythms

Last about 24 hours

Sleep-wake cycle - regular pattern of sleeping and waking can be seen to be controlled by exogenous cues such as light and dark. Psychologists have investigated what happens when we are free of these external cues using temporal isolation studies - we see the impact of our internal body clock

Siffre - spent several occasions living underground free from external cues - no radio, no light - woke, ate and slept when he felt like it - only thing influencing his behaviour was his internal body clock - natural cicradian rhythm settled down to 24 hours but sometimes to 48 hours, changing dramatically - final underground experience was when he was 60 - investigated the effects of aging - biological clock ticked more slowly than his first few experiences - sleep patterns had changed as well case study - unique features may not represent others as his bodys behaviour may not be typical of all people - low population validity - ethics - he had thoughts of suicide after several exposures to isolation - may have effected his body clock - however he was influential in his work - living in a cave may have particular effects - cold - supported by other studies - used an experimental approach - could demonstrate causal relationship

Support by Aschoff and Wever - placed pp's in underground ww2 bunker in the absence of environmental and social cues - most people displayed rythms between 24 and 25 hours though some were a long as 29 hours 

However - early studies allowed pp's to be exposed to artificial light as they didn't think it was an external cue - this may have effected their cycle - Cziesler  altered pp's circadian rhythms down to 22 hours and up to 28 hours by using dim lighting so results in early studies may lack some reliabiity as they were not aware that artifical lighting could act as an external cue

Individual differences - circadian cycles in people can vary from 13 to 65 hours - Cziesler and cycle onset varies - there are innate patterns of sleeping and waking: morning types - 6am-10pm - eveing types - 10am-1am - Duffy so pp's used in experiments such as Aschoff's and Wevers or Folkard's may not represent the individual differences in the global population - they did not test pp's length of cycles or the onset of their cycles so these may have been an extrenous variable in the results as some people may have found it easier to adapt to the manipulation of the biological clock

Cycle's can be entrained to some extent by external cues - Folkard 12 pp's in a cave for 3 weeks - he gradually reduced pp's circadian rhythm by using a quickening clock but at 22 hours the pp's own internal body clock took over and followed a 24 hour cycle - showing a limit for the control of internal rhythms by external cues

Real-world application - Chronotherapeutics is the application of biological rhythms to the treatment of disorders - it is advantageous to take medication r engage in certain acitivites at certain times in the day - taking asprin to treat heart attacks at 11pm - asprin levels the peak in the bloodstream at the time heart attacks normally occur - 3am - people are more alert in the morning and the early evening so those are the best times to work

Core body temp - lowest at 4.30am and highest at 6.00pm. Slight trough just after lunch which is not due to eating as it is common in other culutres who do not eat lunch - having an afternoon siesta could be related to the dip in body temp

Body temp linked to cognitive abilities - Folkard - learning ability of 12-13 yr olds who had stories read to them at either 9am or 3pm - afternoon group showed higher recall and comphrehension recall, retaining about 8% more - suggests long-term recall best when body temp is highest. Gupta - performance on IQ tests was best at 7pm compared to 9am or 2pm - could be a factor used to be considered when taking exams

Giesbrecht lowered body temp by placing pp's in cold water and found cognitive performance was worse on some tasks - it is not clear whether the effect is due to the direct effects of core body temp or whether high core body temp leads to increased physiological arousal and creates this effect - Wright

BUT - Hord and Thompson found no correlation between body temp and cognitive performance