Biological Rhythms

Repeats once every 24 hours, e.g. sleep/wake cycle and body temperature

A: To study effects of biological rhythms when underground for extended periods of time.

P: Siffre spent 6 months in a cave where there were no exogenous zeitbergers, e.g. natural light, but it was artificially lit - Siffre had control over the artificial light. He had contact with an outside world via a telephone and researchers would call regularly at different times each day. His behaviours were constantly monitored. 

F: His 'free-running' biological rhythm was around 25 hours though he did fall asleep and wake up on a regular schedule.

C: Endogenous pacemakers mainly control the sleep/wake cycle and it may be slightly longer than 24 hours but exogenous zeitbeigers, e.g. number of daylight hours, meal times, entrain it to be 24 hours.

Practical application to shift work: Given researchers a better understanding of the adverse consequences that can occur as a result of disruption to cycle - desynchronisation. Night workers in shift work experience a period of reduced concentration at 6am - circadian trough - making mistakes/accidents more likely to happen. Relationship between shift work and poor health that may be due to stress of disruption to sleep/wake cycle. Research into sleep/wake cycle has economic implications in terms of how best to manage worker productivity. 

Use of case studies and small samples: Studies of sleep/wake involve small numbers of participants or individuals - idiographic approach. May not be representative of wider population so there are issues generalising. Effect of individual differences - Siffre developed depression so may have effected cycle because people with depression tend to sleep too much or not enough. Further research found that some people have a natural preference to going to bed late ('night owls') or waking up early ('morning larks'). Also age differences in sleep/wake cycle - in a later study, Siffre found that his internal clock ticked more slowly at 60 than when he was a young man.

Five stages of sleep that altogether last 90 minutes. Continues throughout the night and characterised by different types of brainwave activity monitored using EEGs.

Stages 1+2: 'Sleep escalator' as sleep is light and the person can be easily woken. Sleep spindals occur in stage 2, e.g. feeling that you're falling off a cliff. Brainwaves become slower and go from alpha to theta waves as sleep gets deeper.

Stages 3+4: Delta waves replace theta waves as we move into slow wave sleep (SWS). Hard to wake someone. Sleepwalking/talking may occur.

Stage 5: Rapid eye movement (REM) increases in length throughout the night. Where most dreaming occurs. Brain is very active but body is paralysed. Sometimes called paradoxal sleep. 

Research support: Dement and Kleitman found that 80% of Ps woken in REM sleep reported dreaming and were able to very accurately recall the dreams. Replications of this study has found similar findings. Suggests that REM sleep is an important part of the ultradian sleep cycle and dreaming is universal so must be important. Sleep monitored using EEGs so data is objective, empirical and replicable (as shown) so supports psych as a science.

However, only 9 Ps were used in the original study so there are issues generalising to the population - low in external validity. Ps in a sleep lab and know that their sleep is being monitored in artificial conditions so may have an effect on how they sleep. Ps had to say whether they dreamt or not, which is self-report and so is subjective.

Occur less often than once every 24 hours but more often than annually

Menstrual Cycle

• Controlled mainly by the hormones oestrogen and progesterone
• Takes on average 28 days but varies between individuals
• This is an endogenous rhythm but is affected by external cues - exongenous zeitgeibers - including weight, birth control and stress
• A woman who spent 3 months in a cave experienced the shortening of her menstrual cycle which took time to revert back to normal once she emerged 

S.A.D. - Seasonal Affective Disorder

• Winter depression that affects half a million people from September to April
• Main symptoms are a persistent low mood and a lack of interest in life
• Caused by a biochemical imbalance in the hypathalamus due to the shortening of daylight hours and lack of sunlight
• Lack of light in winter months is thought to have a knock-on effect on the production of serotonin - a chemical linked to the onset of depressive symptoms

Methodological issues: Many factors affect changes in menstrual cycles, e.g. diet, stress. that might have acted as confounding variables. This means any sychronisation was a result of chance. Small sample sizes used - issues generalising - and relies on self-reporting, which is subjective.

Refuting evidence: Yang and Schank studied 186 Chinese women in university accommodation over a year, overcoming methodological issues in McClintock's study, such as cycles being observed over too short a time period and errors in calculating menstrual onset. Found no evidence of synchronicity. 

Evolutionary basis for menstrual cycle: May have been beneficial for our ancestors to menstrate together and therefore fall pregnant around the same time. If one mother were to die, other mothers could breastfeed her child, and newborns could be cared for collectively within a social group, therefore increasing chances of survival.  

SCN:

The suprachiasmic nucleus (SCN) is a bundle of nerve cells in the hypothalamus and is one of the primary endogenous pacemakers. It has a nerve input directly from the retina of the eye so informed about the exogenous zeitgebers of light. Enables body clock to change whilst we are asleep. In lack of light the info is transmitted to the pineal gland that manufactures melatonin (hormone), which stimulates the production of serotonin (neurotransmitter) in the raphe nucleus. This reduces arousal and induces sleep.  When light enters the eyes it stimulates the SCN to stop the production of melatonin by the pineal gland so maintains arousal levels keeping you alert and awake.

Morgan's Mutant Hamsters:

SCN was removed from 20 hamsters. Their circadian rhythms disappeared. Transplanting SCN cells re-established their circadian rhythms. Shows SCN is the main pacemaker. 

Supports psychology as a science: Manipulated IV and measured its affect on DV, so can infer cause and effect - that SCN causes us to have a sleep/wake cycle.

Issues generalising to humans: Particularly as hamsters are nocturnal. They also have different exogenous zeitgebers to humans, e.g. cannot read clocks.

Ethical issues: Animals suffered harm and were at risk when returned to their natural habitat. Cost-benefit analysis required. 

AO2: Sleep disorders can be treated with melotonin, showing the importance of endogenous pacemakers. 

External cues that entrain our biological rhythms

Light

• Resets SCN (main endogenous pacemaker) so plays a key role in maintaining sleep/wake
• Indirect influence of key body functions, e.g.blood circulation
• Suggested that light may be detected by skin receptors sites even if it is not received by the eyes
• Does not rely on the eyes to exert its influence of the brain

Social Cues

• As a child, parents determine bedtimes and mealtimes that influence sleep/wake
• Adapting to local mealtimes and bedtimes an effective way to beat jet-lag

Supporting research: Miles found that a man blind from birth had a circadian rhythm of 24.9 hours and needed stimulants and sedatives to adjust sleep/wake cycle to 24 hours. Shows that light - exogenous zeitgeber - is crucial.

Difficulties generalising: This is a case study so there are issues generalising to the population due to issues of individual differences. Cannot infer cause and effect.

Refuting evidence: Found that those living in the Arctic, where there is no daylight in winter and no darkness in summer, still maintained a normal circadian rhythm. Suggests the influence of exogenous zeitgebers may be overstated.