Biopsychology: Infradian And Ultradian Rhythms Flashcards
Outline Infradian Rhythms.
A biological rhythm with a period longer than a circadian rhythm. I.e with a frequency over 24 hours. They may take days,weeks, months or years. An example is the human menstrual cycle (28 days).
Outline the Ultradian rhythm.
These are processes within the body that involve regular rhythms with a period shorted than a circadian rhythm. I.e shorted than 24 hours. An example is the is the sleep cycle (not to be confused with the sleep/wake cycle). This is 90 minutes long.
Some research has suggested the menstrual cycle (an infradian rhythm) can be entrained by the pheromones of other women.
McClintlock collected daily samples of sweat (containing pheromones) from 9 women which were
then then applied to upper lips of 20 other female participants. McClintlock found that 68% of the odour recipients experienced changes to their menstrual cycle that brought them closer to the cycle of their odour donor. The fact that the odour recipients menstrual cycle changed in response to an external stimulus
suggests that the menstrual cycle can be entrained by exogenous zeitbegers. This demonstrates that
at least some infradian rhythms can be entrained, just like circadian rhythms. However, this study’s
findings have proven difficult to replicate by other researchers. There is therefore reason to doubt
the conclusion that the menstrual cycle can be entrained by exogenous zeitgeibers.
How has research helped us understand a type of ultradian rhythm called the sleep cycle?
Dement and Kleitman (1957) monitored nine sleeping particiapnts. Using EEG, they identified 5 stages of distinct brain activity. They found in one of these stages, the eyes of the patients moved rapidly, so they called this stage REM and the other 4 stages NREM. Participants woken from REM sleep were much more likely to report dreaming than those in NREM sleep. This study was pioneering as it allowed researchers to identify and understand a new type of
ultradian rhythm: the sleep cycle. Moreover, the finding that participants recalled more dreams in
REM sleep helped develop scientific knowledge of the nature of dreams, which had previously been
regarded as a mysterious phenomena. Further support for this study’s findings on the nature of the sleep cycle comes from its use of EEG to investigate the brain. An EEG takes readings of the brain every millisecond, giving EEG high temporal resolution. This means this study’s findings on the timings of the different stages of sleep are likely to be very accurate. However, this study’s findings have been criticised for weak population validity, as the small sample size means that generalising from this sample’s sleep cycle to a general law on how everyone’s sleep cycle works is problematic.
Researchers have investigated how the stages of the sleep cycle can affect cognitive performance.
Rasch and Born (2013) found that in rats, REM sleep not only increases following periods of
intensive learning, but that REM sleep deprivation can inhibit a rat’s performance on a maze escaping task which had been previously been learnt. These findings suggest a link between the REM stage of sleep and an animal’s ability to learn.
This suggests that dreaming plays a role in learning. This shows how understanding the sleep cycle
(an example of an ultradian rhythm) has practical applications, as it shows the value of high-quality
sleep (i.e., sleep that supports all stages of the sleep cycle) for effective learning. However,
generalising from this research to humans may be difficult given the biological and social differences
between rats and humans. There are therefore reasons to doubt this study’s conclusions on the
effect of ultradian rhythms like the sleep cycle on human learning. Although this study demonstrates that REM sleep may play a role in learning, it does not explain why it is important. Some researchers have suggested that dreaming plays an important role in consolidation of
memories, integrating information learned during the day into long-term memory
