> The most obvious infradian rhythm is the human female menstrual cycle driven by fluctuating hormone levels.
> Less well known infradian rhythms are the monthly rhythms affecting males.
> EMPSON did a study where 21 male participants had their body temperature & alertness levels measured over periods of 49-102 days. Found some evidence in males for a periodic variation in temperature & morning alertness, with a cycle of about 20 days.
Seasonal affective disorder (SAD)
> Infradian rhythms don't have to be monthly, some can be once a year, such as seasonal affective disorder (SAD).
> SAD - depressed during the winter months and recover during the summer (we may all experience some lowering of mood when there's more darkness than daylight but SAD sufferers experience severe symptoms).
> SAD - studies show the hormones melatonin & serotonin are secreted when it's dark (by the pineal gland); more darkness = more melatonin & more melatonin = less serotonin (as melatonin is produced from serotonin). Low levels of serotonin = depression.
Exogenous cues -
> The menstrual cycle is normally governed by an endogenous system (the release of hormones under the control of the pituitary gland) but can be controlled by exogenous cues.
> Research has shown that when several women live together and don't take oral contraceptives, they tend to menstruate at the same time every month.
> RUSSELL ET AL. did a study where daily samples of sweat were collected from 1 group of women and rubbed on to the upper lip of women in the second group. The groups…