infradian rhythms

• an infradian rhythm is a biological rhythm with a frequency of less than one cycle in 24 hours
• an example of an infradian rhythm is the menstrual cycle and seasonal affective disorder
• within the menstrual cycle, hormones act as a endogenous pacemake
• stern and mcclintock (1998) - menstrual cycles may synchronise as a result of the influence of pheromones

  studied 29 women with irregular periods

  found that 68% of women experienced changes to their cycle, which brought them closer to the cycle of their “odour donor”
• seasonal affective disorder (SAD) is a type of depression that occurs during the winter months

  it is considered a circannual rhythm (subject to yearly cycle) and also is classed as a circadian rhythm as it may be due to the disruption of the sleep/wake cycle
• melotonin is one of the causes of SAD, the pineal gland secretes melotonin until dawn (when there is an increase in light) and due to a lack of light in the winter mornings the secretion process is longer

  this has a knock-on effect on serotonin, which is linked to the onset of depressive symptoms