infradian and ultradian rhythms

• infradian rhythms last longer than 24 hours and can be weekly, monthly or annually
• examples of infradian rhythms- female menstrual cycle, seasonal affective disorder, hibernation (in animals)
• research suggests infradian rhythms are heavily influenced by exogenous zeitgebers
• Reinberg 1967 examined a woman who spent three months in a cave with only a small lamp to provide light. Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days
• this result suggests the lack of light an exogenous zeitgeber in the cave affected her menstrual cycle, (reinberg woman who went from 28-25.7 day menstrual cycle)
• Ultradian rhythms last fewer than 24 hours
• another ultradian rhythm is appetite or meal patterns in humans
• infradian- longer than 24 hours, circadian- 24 hours approximately, ultradian- less than 24 hours
• infradian rhythm- lasts for longer than 24 hours and can be weekly, monthly or annually- eg female menstrual cycle, monthly, regulated by hormones
• while it is logical to assume that infradian rhythms (particularly the menstrual cycle) are governed by internal factors (endogenous pacemakers) such as hormonal changes, research suggests that these infradian rhythms are heavily influenced by exogenous zeitgebers.
• another example of an infradian rhythm- seasonal affective disorder- infradian rhythm related to the seasons (yearly cycle)
• seasonal affective disorder (SAD)- (can think of an acronym for winter blues), melatonin is said to be secreted by the pineal gland at night. longer nights= increased melatonin secretion, so the lack of light around the time of winter months can be linked to an increase in depressive symptoms
• research into infradian rhythms- reinberg (1967) examined a woman who spent 3 months in a cave, with only a small lamp to provide a source of light, reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days... these results suggest a lack of light (an exogenous zietgeber in the cave affected her menstrual cycle, and therefore demonstrates the effect of external factors on infradian rhythms.
• russell et al (1980) found that female menstrual cycles became sychronised with other females through odour exposure, in one study, sweat samples from one group of women were rubbed onto the upper lip of another group. Despite the fact that the two groups were separate, their menstrual cycles synchronised.