Infradian and Ultradian Rhythms

• Ultradian rhythms last for less than a day. The cycle repeats itself more than once in 24 hours. An e.g. is the sleep cycle that has 5 stages and lasts for 90-100 minutes.
• Ultradian e.g.

  • within the sleep/wake there is an ultradian rhythm
  • repeats every 90-100 minutes
  • there are five different stages and 4 stages of NREM and 1 state of REM
  • deep sleep may only occur within the first couple cycles
  • REM is where dreams occur
  • as we age we may have less deep sleep and this declines more gradually for females
  • may be individual differences
• Infradian rhythms last for longer than a day.
• Infradian e.g.

  • menstrual cycle
  • sex hormone cycle on average lasts for 28 days and is regulated by hormones
  • ovulation occurs halfway through and lasts 16-23 hours
• Annual rhythms - seasons, e.g. mood in humans, heart attacks vary seasonally, and peak in winter. Most deaths occur in January

  Non human animals hibernate
• A03

  Although the menstrual cycle is an endogenous system, evidence suggests that it may be influenced by the exogenous factors of other women.

  • Stern and McClintock
  • 29 women with a history of irregular periods were the sample
  • Pheromones gathered from 9 of the Ps armpits and were treated with alcohol, then frozen
  • on day 1, the pads from the start of the menstrual cycle were rubbed on the upper lip of the other 20 women
  • then the day 2 pad was used on the next day and so on
  • 68% women experienced changes to their cycle that brought them closer to the cycle of their "odour donor"
• A03

  Penton-Voak et al suggests that human mate choice varies across the menstrual cycle.

  In the ovulation phase, women preferred more masculinised faces and at other points women preferred more feminised faces.

  This suggests women look for kindness and cooperation in parental care inlong term mates and a preference for males with good genes for short term liasions which is beneficial to offspring, thus the menstrual cycle affects mate choice.
• A03

  Dement and Kleitman. Studied 9Ps in a sleep lab that were controlled for caffeine and alcohol. . Dement and Kleitman (1957) investigated this using EEGs and found that REM sleep was closely linked to dream recall, suggesting a distinct rhythm within sleep.

  Ps woken up during REM sleep had a significantly better recall of dreams than Ps who woke up during other sleep cycles

  • Their use of objective measures like brainwave activity gave the study strong scientific validity and helped confirm the structure of the sleep cycle. However, the study was based on a small sample and involved sleeping in a lab setting, which may not reflect natural sleep behaviour, limiting ecological validity. Nonetheless, the findings offer strong support for the existence of ultradian rhythms and remain foundational in sleep research.