BIOLOGIAL RHYTHMS: CIRCADIAN RHYTHMS
Overview
circadian rhythms = biological rhythms, subject to a 24 hour cycle, which regulate a number of body processes such as the sleep/wake cycle and changes in core body temperature
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)
SCN
the eye provides information about light, setting the body clock to the correct time each day (photoentrainment)
the SCN uses the information to coordinate the activity of the entire circadian system
the suprachiasmatic nucleus (SCN) is the master circadian pacemaker, in hypothalamus
eg. if light levels are low, the SCN communicates with the pineal gland to secrete melatonin
The sleep/wake cycle
levels of light and darkness are the external signals that determine when we feel the need to sleep and wake up
homeostatic control
dictates when we should be sleeping but also when we should be awake
homeostasis tells us that the need for sleep is increasing because of the amount of energy used up during wakefulness
the homeostatic drive for sleep increases gradually throughout the day, reaching it maximum in the late evening when most people fall asleep
the sleep/wake cycle is controlled by the homeostatic control
the circadian 'clock' is described as 'free running'. means that the absence of external cues, the sleep wake cycle will still maintain at about 24-25 hours
Michel Siffre 1975 AO3
key findings: it settled into a sleep/wake cycle of 25-30 hours
he lost track of how many days he had been in the cave, believing it to be one month less
French cave explorer spent 6 months in a cave with no natural light or cues as to the day or time
conclusion: suggests circadian rhythms persist despite isolation from natural light, demonstrates he existence of an endogenous clock
shows external cues are important as his sleep wake cycle was not exactly 24 hours
Michel Siffre evaluation
😢 case study, individual differences, lacks population validity
😃 also an experiment, controlled key variables (exogenous zeitgebers) to observe the effect on his sleep wake cycle. demonstrating a causal relationship
aschoff and wever 1967
ppts were place in an WW2 bunker, in the absence of environmental an social time cues
ppts displayed a circadian rhythm between 24/25 hours, some were as long as 29 hours
Subsequent studies above ground have confirmed the findings of Siffres research
shows sleep/wake cycle operates in the absence of external cues
individual differences
both studies have small samples and it seems that sleep wake cycles vary widely from person to person
duffy 2000: morning people (larks) prefer to rise early and go to bed early (about 6am to 10pm)
generalisations are difficult to make
evening people (owls) prefer to wake and go to bed later (10am to 1pm)
difficult to use the research data to discuss anything more than averages, which may be meaningless