- occurs once every 24 hours
- The sleep/wake cycle is an example
- Are affected by exogenous pacemakers or zeitgebers : light , clocks ,weather, temperature , social life .. etc
- are affected by endogenous pacemakers : which is an internal body clock or oscillator.
- occurs less than once a day on a yearly basis
- an example is the 28 days menstrual cycle , another is hibernation in squirrels and hedgehogs and another is Seasonal affective disorder (SAD)
- Occurs more than once every 24 hours .
- an example is : sleep cycle , REM and NREM.
- Siffre found that the sleep- wake cycle last for 25 or 24.9 hours ; when he lived in a cave in Texas to test effect of 'free-running' biological rhythms. This study also shows the importance of exogenous zeitgebers as the light affect him because he could not synchronise.
-Miles et al (1977) did a study that matched Siffre's. They studies a young male who was blind from birth and found that he had a 24.9 hour wake cycle . However he had been taking tables…