Biological Rhythms (EPM & EZ + Circadian Rhythms)
What is a circadian rhythm?
A Circadian Rhythm is a biological rhythm that follows the cycle of a day- around once 24 hours.
What is a biological rhythm?
A biological rhythm refers to a change in bodily processes in response to specific changes in the environment.
What is the third and final bit of application that support circadian rhythms?
Application to Education: Kelly (2010) looked at teenage circadian rhythms. They seem to start and end 2 hours later. Moved school time to 10-6 and found increased social and academic success.
What is the second bit of application that support circadian rhythms?
Application to Medicine: Circadian Rhythms govern bodily processes including heart rate and temperature. Using these to maximise effectiveness of medicine in schedules (Baraldo 2008)
What is the first bit of application that supports circadian rhythms?
Application to Work Environment: Boivin (1996) natural attentional laps at 6:00am linked to increased rise in accidents. Knutsson (2003) shift workers 3x more likely to have heart disease. Apply to change conditions and laws around shift workers.
What did Aschoff and Werner (1976) do?
Aschoff and Werner convinced a group of pps to spend 4 weeks living in a WW2 bunker.
What positive research is there for our exogenous zeitgebers?
Czeisler (1999) - Even artificial light can alter circadian rhythms between 22-28 hrs. Murphey (1998) - Evidence that light is such an important exogenous zeitgaber it can be detected without eyes. 15pps were woken up by light shone on the back of their knees. Concurrent validity.
Who showed that artificial light could be used to change circadian rhythms hours?
Czeisler (1999) found Artificial light could be used to change circadian rhythms between 22- 28 hrs.
What is the sleep / wake cycle?
Daily cycle of biological activity in a 24 hour period based on regular environmental cues. Where humans feel more awake for most of the day and more tired for the night.
What is a weakness for endogenous pacemakers?
Evidence suggests that we have many EPMs which can work independently of each other. Daimola (2000) showed that changing feeding times in hamsters altered CR of liver leaving CR of SCN unaffected.
What are exogenous zeitgebers + example?
External cues which affect or entrain our biological rhythms. EG: Daylight in sleep wake cycle
Finally, what did Folkard do?
Folkard aimed to see if he could manipulate the endogenous pacemaker by changing the exogenous zeitgaber.
What did Siffre find?
Found that without Exogenous Zeitgabers his circadian rhythm was around 25 hours. Found that he lost track of time, thought it was mid August when it was mid September.
What did Folkard find?
He found that all but one pp was able to comfortably adjust to the unknown change.
How did Folkard do this?
He got 12 participants to spent 3 weeks in a cave, sleeping when a clock showed 11:45 waking at 7:45. Over the study, the time between was shortened by 2 hours.
What else did Czeisler find?
Individual Differences. Cziesler (1999) found CRs range between 13-65 hours! Duffy (2001) found morning lark and night owl preferences actually exist
What are endogenous pacemakers + example?
Internal body-clocks which regulate our biological rhythms. EG: Suprachiasmatic Nucleus.
What are the two key examples of a circadian rhythm?
Key Examples: 1. Sleep/ Wake Cycle 2. Core Body Temperature
What is our most powerful exogenous zeitgeber & how does it help?
Light. One of the most powerful EZs. Crucial in the regulation of the sleep wake cycle. Directly linked to melatonin production and therefore sleeping.
What is a second weakness for exogenous zeitgebers?
No one has replicated Murphey's research. Decreasing reliability.
What 3 bits of research is there for circadian rhythms?
Siffre (1962) Aschoff and Werner (1976) Folkard et al (1985)
What supporting evidence is there for the interaction of endogenous pacemakers and exogenous zeitgabers?
Siffre (1962) & Aschoff and Werner (1976): Supporting interplay between the two.
What was the aim of Siffre's study?
Siffre (1962) aimed to study his 'free running' endogenous pacemaker. He spent an elongated period (2 months) in a cave without any external communication or daylight.
What are the weaknesses for evaluation of circadian rhythms? Sample size? Control of case studies?
Small samples/ case studies: All of these have small samples or use individual. Siffre (1999) age 60 noted in his circadian rhythm had slowed. Cannot generalise to general population Poor Control. Case studies typically use artificial light, but this may still act as an exogenous zeitgaber.
What is a strength for the research gone into circadian rhythms? SE?
Supporting Evidence: Siffre (1962) Aschoff and Werner (1976) Folkard (1985) All show impacts of circadian rhythms - Concurrent Validity
What supporting evidence is there for endogenous pacemakers?
Supporting evidence of EPM: (Ralph 1998) (DeCoursey 2000) - Concurrent Validity Supporting evidence for interaction of EZ and EPM: (Siffre 1962) (Aschoff and Werner 1976) supporting interplay between the two.
What is a first weakness for exogenous zeitgebers?
The impact of Zeitgebers overstated: Miles et al (1977) - blind man (from birth) unable to develop normal circadian rhythms without sedatives and stimulants. Decreasing validity.
What are the two things that control biological rhythms?
These are controlled by 2 things: Endogenous Pacemakers (Internal body clock) Exogenous Zeitgebers (External factors)
What did Aschoff and Werner find?
They found that all participants except 1 were found to have circadian rhythms of between 24-25 hours. The exception had a 29hour circadian rhythm.
What do our exogenous zeitgebers allow us to do?
They have the ability to entrain our circadian rhythms through interaction with our EPMs. (entrain: to bring along with. So to bring an EPM inline with EZs)
