Another example of an ultradian rhythm is the basic rest-activity cycle(BRAC). Friedman and Fisher observed the eating and drinking behaviours of an group of psychiatric patients. They discerned a clear 90 minute cycle in their behaviour. The importance of this 90 minute rhythm is probably as a form of timing to ensure that the biological processes in the body work in unison, in the way that a conductor keeps an orchestra in time. A rudimentary criticism of the experiment may be that the patients (the participants) were in a facility where their food and drink was brought to them at certain times of the day, they had no dictation over when they could or couldn’t eat and drink, which some would say casts doubt on the validity of the results.
Infradian rhythms are bodily cycles that last more than 24 hours but less than a year , for example the menstrual cycle and Seasonal Affective Disorder (SAD). The menstrual cycle spans over a period of 28 days. The cycle starts with the ripening of an egg and the thickening of the lining of the womb. Various hormones maintain the lining with the cycle ending with the shedding of this lining. The release of these hormones are co-ordinated by the pineal gland which is speculated to be influence by light levels and the secretion of melatonin.
McClintock conducted a case study (long span of 10 years) than involved 29 women who had a history of irregular, spontaneous ovulation. They wore cotton pads under their arms (to transfer sweat to it) which they were told to wear for 8 hours. They were also instructed to bathe with unperfumed products so it wouldn’t interrupt the study of their sweat and the pheromones which it contains. Then the sweat pads were treated with alcohol and frozen. These pads were then wiped under the noses of the other women on a daily basis. A staggering 68% responded to the pheromones with their respective cycle lengths synchronising with the other person’s (who’s pheromones had been collected) menstrual cycle. Evident from this study is that pheromones are exogenous zeitgebers that exert a degree of influence on the infradian rhythm, specifically the menstrual cycle. This is further supported by Russell’s study which used the same procedure and had similar findings, the groups being kept separate yet their menstrual cycles synchronised with their individual donor. Both of their studies were controlled lab experiments , with extraneous variables being censored (e.g. the interaction of the donors with the recipients, using un-scented products ect…) allowing us to draw causal relationships between pheromones and the menstrual cycle.
PMS (Post Menstrual Syndrome) is a disorder that affects many women due to the hormone imbalance. Dalton found that PMS was associated with an increase in crime, accidents and suicide. PMS has been used as a legal defence in the case of Miss English who killed her husband during PMS and was aquitted of all charges . Dalton argued that severe PMS was akin to a mental disorder and therefore individuals should not be held accountable for their actions. This suggests that biological rhythms may be beyond our control. On the other hand, there is evidence that we can ‘will’ our biological rhythms to change. One study found that people who were told to wake up at earlier times of the night than usual had higher levels of the stress hormone ACTH (which contributes to the waking-up process)
Another example of an infradian rhythm is Seasonal Affective Disorder (SAD). It is common for people to experience ‘winter blues’ but people with SAD have a more severe form of this, showing symptoms of chronic depression through the darker months. This may be due to an increase in the production and secretion of melatonin which happens in the dark. The longer time spent in the dark, the greater levels of serotonin and melatonin secreted. The main criticism of this explanation of SAD is that it focuses primarily on it being a natural outcome of infradian rhythms, but alternatively it could be the consequence of a disrupted circadian rhythm. In the UK, as the seasons change from summer to winter, the circadian rhythm may be thrown out of phase. People continue to get up at about the same time but often go to sleep earlier because it is darker earlier. This means that the biological system gets the impression that time is shifting and the result is similar to jet lag, which may explain why explain why the symptoms of SAD are similar to those of jet lag.
by
ajama (student)
