Ultradian & Infradian

• Infradian rhythms are biological rhythms with a frequency of less than one cycle in 24 hours e.g. menstruation, SAD, migration
• The Menstrual cycle is an infradian rhythm governed by monthly changes in hormone levels (endogenous pacemakers) that regulate ovulation
• The hormones involved in mestruation are FSH, LH< oestrogen, and progesterone
• Oestrogen triggers the release of an egg
• Progesterone causes thickening of the lining of the uterus
• The menstrual cycle is an endogenous system however may be influenced by exogenous factors e.g. synchronisation
• Stern & McClintok investigated synchronisation using 29 women with a history of irregular periods and transferring their pheremones to other participants
• Stern & McClintok tranferred the pheremones by freezing pads of armpit sweat and extracting the pheremones to place under the upper lip of other participants
• Stern & McClintok found that 68% of participants experinces changes to their cycles which brought them closer to that of the other woman's
• Seasonal Affective Disorder is an infradian rhythm where persistent lwo mood and lack of activity/interest is caused by the shorter daylight hours in winter months
• Seasonal Affective Disorder is a circannual rhythm as it is a yearly cycle
• Seasonal Affective Disorder may be caused by disruption to the sleep-wake cycle due to melatonin secretion lasting longer in the darker mornings
• Ultradian rhythms are biological rhythms with a frequency of more than one cycle in 24 hours
• The stages of sleep are an ultradian rhythm with 90-minute cycles
• The 1st and 2nd stages of sleep are light sleep, where a person can be easily woken
• Stages 1 & 2 produce alpha waves
• Alpha waves have a high frequency and short amplitude
• The 3rd and 4th stages of sleep are deep/slow wave sleep
• Stages 3 & 4 produce delta waves
• Delta waves have a low frequency and high amplitude
• The 5th stage of sleep is REM sleep, where the body is paralysed and most dreams occur
• Stage 5 of sleep produces theta waves
• Theta waves have a low frequency and high amplitude
• The Basic Rest-Activity Cycle (BRAC) is an ultradian rhythm with 90-minute cycles that occurs during waking hours
• BRAC is a period of alertness followed by a spell of physiological fatigue e.g. loss of concentration, hunger
• Ericsson et.al. investigated BRAC by studying violoinists
• Ericsson et.al found that the best results came from violinists who practiced 3 sessions a day for no longer than 90 minutes
• There is research to support the effects of light on SAD e.g. Rosen et.al.
• Rosen et.al. measured rates of SAD in multiple states across the USA and found the highest rates in New Hampshire and lowest rates in Florida