Infradian and ultradian rhythms

• Infradian rhythms are biological rhythms that happen over a time period of more than 24 hours
• Ultradian rhythms are biological rhythms that happen over a period of less than 24 hours
• Example of a infradian rhythm is the menstrual cycle which is subject to around 28 days
• Example of an ultradian rhythm is the sleep cycle
• The menstrual cycle is an infradian rhythm that is governed by the endogenous pacemaker of hormone changes
• The menstrual lasts around 28 days but anywhere between 24 and 35 is considered normal
• During the menstrual cycle rising oestrogen levels cause the ovary to develop an egg; this is ovulation
• during the menstrual cycle progesterone levels cause the womb lining to grow however if pregnancy does not happen this lining sheds
• Research suggests that the menstrual cycle can be impacted by exogenous zeitgebers such as the presence of other women and their menstrual cycle
• Seasonal Affective Disorder (SAD) is an infradian rhythm that is characterised by DSM-5 as a form of depression that has a seasonal pattern of onset
• Seasonal Affective Disorder (SAD) is triggered in the winter months as the exogenous zeitgeber of light is reduced causing the pineal gland to produce higher levels of melatonin altering levels of serotonin leading to depressive symptoms
• Seasonal Affective Disorder (SAD) is a circannual rhythm as it is subject to a yearly cycle
• The sleep cycle is a ultradian rhythm that is often studied using electroencephalograms (EEGs)
• Sleep cycle stage 1; Light sleep with high frequency and low amplitude brain waves called alpha waves
• Sleep cycle stage 2; light sleep where alpha waves continue but random changes take place called sleep spindles
• Sleep cycle stages 3 & 4; deep or slow wave sleep where delta waves with low frequency and high amplitude take place
• Sleep cycle stage 5; Rapid Eye Movement (REM) sleep where the body is paralysed but brain waves resemble the awake brain with theta waves causing dreams to occur
• Stern and McClintock (1998) aimed to investigate the impact of exogenous zeitgebers on women's periods
• Stern and McClintock (1998) used a sample of 29 women with irregular periods
• Stern and McClintock (1998) took pheromone from 9 of their participants via a cotton pad on the armpit for at least 8 hours
• Stern and McClintock (1998) treated the pheromone pads with alcohol and froze them before placing them on the upper lips of the other participants
• Stern and McClintock (1998) found that 68% experienced changes to their menstrual cycles so that it was closer to that of their "odour donor"
• Infradian rhythms strength; supported by evolutionary psychology as rhythms such as the menstrual cycle syncing would be adaptive to make women have children around the same time to increase chances of survival by providing a larger number of caregivers
• Infradian Rhythms strength; understanding of Seasonal Affective disorder has allowed treatments to be developed such as light therapy which Sanassi (2014) observes as being 80% effective in treating symptoms of SAD
• Stern and McClintock (1998) weakness; extrenuous variables as many factors such as diet and exercise can impact the mestrual cycle causing lowered validity as these EVs were not controlled
• Ultradian rhythms strength; allowed understanding of age related changes in sleep such as the slow wave stage reduces with age explaining reduced alertness in old age allowing medication to be developed to solve the issue
• Ultradian rhythms strength; research into the sleep wake cycle uses Electroencephalograms (EEGs) which must be done in a lab meaning extraneous variables are controlled and research is highly valid and reliable
• Ultradian rhythms weakness; some individuals experience differences in their sleep cycles for example Tucker (2007) found differences in participants 3rd and 4th stages showing that sleep cycles vary making research hard to generalise