Circadian Rhythms

Circadian Rhythms

Evaluation

Support From Case Studies

Practical Application to Shift Work

Practical Application to Drug Treatments

• Support from Siffre, Aschoff and Wever, and Folkard.

• Given researchers a better understanding of the consequences of a disrupted circadian rhythm.
• Night workers engaged in shift work experience a period of reduced concentration around 6 in the morning, making accidents more likely.
• Knutsson found that shift workers are three times more likely to develop heart disease which may be due to the stress of adjusting to different sleep/wake patterns.

• Circadian rhythms co-ordinate a number of the body's basic processes such as heart rate, digestion and hormone levels.
• This has improved understanding of drugs and when to take them.
• Research shows there are peak times during the day or night when drugs are likely to be at their most effective.
• For example, the risk of heart attack is greatest in the early morning so drugs should be taken at night so they are effective in the morning.

Individual Differences in Case Studies

Poor Control in Case Studies

• Studies tend to involve small groups of participants or single individuals.
• These people may not be representative of the wider population which limits generalisation.
• When Siffre was 60, his internal clock was slower in the cave than before.
• There are also individual differences, as Czeisler found cycles can vary from 13 to 65 hours.
• Duffy also revealed that some people display a natural preference to going to bed early and rising early, but some do the opposite.

• There was also poor control in these studies as although they were deprived of natural light, they were still exposed to artificial light.
• When Siffre woke up, he turned a light on until he went to sleep and he assumed it would have no effect on his free-running biological rhythms.
• However, Czeisler was able to adjust participants circadian rhythms in tests from 22 hours to 28 hours using dim lighting.

Biological Rhythms

Folkard

• We should not overestimate the effect of environmental cues.
• Folkard studied a group of 12 people who agreed to live in a dark cave for 3 weeks.
• They went to bed when the clock said 11:45pm and rising at 7:45am.
• Over the study, the researchers gradually sped up the clock so a "24" hour day was only 22 hours.
• Only one participant was able to adjust to the new regime.

Aschoff & Wever

• Convinced a group of participants to spend 4 weeks in a WW2 bunker without natural light.
• All but one participant displayed a circadian rhythm between 24 and 25 hours.
• Suggests the natural sleep/wake cycle is slightly longer than 24 hours.
• This is entrained by exogenous zeitgebers associated with our 24 hour day.

Siffre's Cave Study

• Michael Siffre spent several extended periods underground to study the effects of his own biological rhythms.
• He was deprived of natural light and sound.
• He monitored many different biological rhythms and found they became free-running.
• Sleep/wake cycle increased to 25 hours but continued to sleep and wake on a regular schedule.

Biological Rhythms

• All living things are subject to these rhythms, and they have an important influence on the way in which body systems behave.
• They are governed by the body's internal biological 'clocks' (endogenous pacemakers) and external changes in the environment that have an effect on the internal regulations (exogenous zeitgebers).
• Circadian rhythms follow approximately a 24 hour cycle.
• These include the sleep/wake cycle and body temperature.

Sleep/Wake Cycle

• We tend to feel drowsy when it's night and dark.
• We feel more alert during the day when it's light.
• Suggests daylight is an important exogenous zeitgeber on our sleep/wake cycle.
• Several studies have investigated what would happen if we didn't have these influences from the environment.