CIRCADIAN RHYTHMS

Biological rhythms are cyclical changes in the way the body functions--> circadian last about 24 hours  sleep-wake cycle & body temp. cycle --> controlled by internal biological 'clocks': endogenous pacemakers .. and external cues: exogenous zeitgebers light /time /social cues

SIFFRE 1975 research into free-running circadian rhythms in sleep-wake cycle

Long periods of time living underground .. only relied on his internal 'clock' --> 1st: 61 days .. resurfaced on 17th Sept thought it was 20th August --> 2nd: 6months Texan cave .. AGE: internal 'clock' ticked more slowly--> circadian rhythm 24 hours but predominantly run by internal endogenous system .. also influenced by external cues too (variation from 24-48 hrs)--> Case studies lack external validity.. (cave cold?)..generalisabilty ..

SUPPORTED BY Aschoff and Wever --> larger sample: P's placed in  WWII bunker w/out environmental & social cues--> P's circadian rhythms b/twn  24 &

25 hours with few as long as 29 hours --> shows cycle operates in absence external cues --> free-running cycle about 25-25 hours.

Folkard: exp. to see if external cues could be used to override internal clock --> 12 P's in cave 3 weeks isolated from natural light and time cues --> circadian rhythm matched the clock (22hours) h/w as clock quickened their rhythms ceased to match and followed 24 hours cycle rather than 22 imposed by exp.

H/W research into circadian rhythms criticised for allowing artificial light --> Research suggests that artificial lighting not important factor: Czeisler altered P's circadian rhythms down to 22 hours up to 28 hours dim lighting

Another circadian rhythm is in variation in body temp --> Body temp. example of of endogenous system -->  FOLKARD tested  12/13 y.o children .. stories read at 9am or 3pm--> 1week passed.. afternoon group superior recall & comprehension.. retained 8% more meaningful info than morning group --> long-term recall best when body temp. highest --> Supported by GUPTA IQ tests best at 7pm than 9am or 2pm ---> A real world application of this research .. teach/test children in afternoon --> H/W field study found

no diff. in cognitive abilites when tested on a field

Hormone levels found to fluctuate in a circadian pattern led to Real world application: Drug treatments --> circadian rhythm affects digestion, heart rate, hormone secretions etc. should be taken into acount when taking drugs --> I.E. aspirin to treat heart attacks most effective around 11pm .. allows aspirin to peak in blood stream

Biological and determinist approach --> sleep-wake patterns are fixed by internal mechanisms --> young blind man: light didn't reset rhythm.. various external cues had little effect on his internally set circadian rhythm --> H/W determinist view misleading .. internal mechanism powerful but flexbility in system --> > FREE WILL: eating/drinking habits etc