Biological Rhythms

Circadian- Takes place over a 24 hour period, prime example being the Sleep/Wake Cycle.

Ultradian- Lasts less than 24 hours, Usually about 90 minutes and often recurring throughout the day. For example our nightly sleep cycle. (NREM and REM)

Infradian- Lasts longer than 24 hours and generally a few times a year. Eg. A womens monthly menstrual cycle.

Sleep/Wake Cycle

 Michael Siffre- Spent 7 months in a cave. Sleep/Wake cycle settled at a steady 24.9 hour pace. Shows Cycle is innate but Zeitgeibers keep in line with 24 hour day. Case Study. Generalisation.

Wilson et al- Blind man, had a steady 24.9 circadian rhythm. Supports Siffre. Needed help resetting cycle with medication. Shows importance of light as Zeitgeiber.

Folkard- Young women isolated herself from environmental cues in a cave. Shifted to 30 hour cycle. Slept for 16 hours. Body temperature remained the same. Against innate rhythms,

Metabolic Rate

Colquhuon- peaks at 4pm and dips at 4am. Also a post lunch dip. To allow for Digestion?

Should have a post lunch nap to allow for this dip and follow this innate cycle.

Body Temperature

Heat is a by product of our metabolic rate so our temperature will follow the same cycle. Will peak at 4pm and dip at 4am (circadian trough).

Bollani et al- Study on newborn babies. Within two days they were all following a similar 24 hour temparature cycle. Too young to be responding to Zeitgeibers. Small study.

Sleep Cycle

It is though that ultradian rhythms are formed even as early as in the womb when we are still a foetus.

• EEG Rhythms recorded in pre term nenonates
• CNS movement recorded as early as 20 weeks.

 Carlson- Medulla controls NREM and REM cycles during sleep.

Bollani- Babies temperature dips and rises a few times a day, only minimally though.

Much of the research into Ultradian rhythms are scientific and therefore objective. Also empirical and therefore can't be falsified. Giving us little reason to doubt.

Menstruation

Reinberg- A women spent 25 days isolated in a cave with no environmental cues. Her day lengthened to 24.6 hours but her menstrual cycle shortened to 25.7 days. Post experiment it took a year for her cycle to return to normal (pre experiment). Showing a lack of light effects our infradian rhythms,

It is common for woment that live together such as siblings, friends, boarding school students etc to synchronise their menstrual cycle.

Russell- Suggested this was due to molecules from bodily fluids etc that carry in the air settiling in nose and activating neurons that in turn actuvate the hypothalmus where the SCN is located as we know this is one of our main endogenous pacemakers as it controls hormone releases that cause periods to synchronise.

He proved this by taking sweat from under the arm of participants, sterilising it using alcohol then placing it on the top lip of another group of participants on a daily basis. Before long they found the participants cyles synchronised with their sweat donors.