Disruption Of Biological Rhythms Evaluation Essay

Zucker’s study where he damaged the SCN in rats to disrupt circadian rhythms was an animal study and may not apply to humans due to differences in anatomy. Therefore it may lack external validity and generalisation in humans. There are also ethical concerns when it comes to intentionally harming such animals although others may argue the benefits gained in understanding animal biology may lead to further understanding of humans. Such studies are typical of the biological approach to understanding human behaviour. They propose behaviour can be explained due to biological structures in the brain or hormonal activity. In truth our behaviour is much more complex and not so deterministic as such biological explanations propose. “Nurture” is evidently a strong factor too with environmental influences and exogenous zeitgebers clearly having a strong role in overriding internal biological clocks to some degree. On the other hand Miles et al demonstrated how a blind man who had a circadian rhythm of 24.9 hours struggled to reduce his internal pace no matter what exogenous zeitgebers were used highlighting some biological clocks may be more ingrained and not influenced.

The SCN is evidently not the only biological clock as other studies have shown that there are other oscillators in the body that appear to regulate biological rhythms through other means (temperature, light penetrating other parts of the body) and explaining circadian rhythms as simply dictated by the SCN and pineal gland connection is oversimplifying the workings of human biology which is far more complex.

Understanding circadian rhythms has real world applications particularly in the field of Chronotherapeutics. This is the study of how timing affects drug treatments and as the circadian rhythm affects digestion, heart rate and hormones among other functions, this can be taken into account when consuming drugs. For instance medicine that affect certain hormones may have no effect if taken when the target hormone level is low but more effective if taken when they are high. Aspirin for example is most effective in treating heart attacks and most effective if taken in the late evening as most attacks occur in the early hours of the morning.


This is an essay answer taken from the paper 2 ebook for AQA psychology A level students studying paper 2 as part of their AS and A level psychology course (new specification). You can download all the possible essay questions and model answers in this paper 2 ebook by clicking the image cover at the top.


How to reference/cite/link to this article: 

<a href=”https://www.loopa.co.uk/circadian-rhythm-biological-rhythms-aqa-psychology/”>Circadian Rhythms – Biological rhythms</a>

Making A level psychology easier

The consequences of disrupting biological rhythms - shift work and jet lag
What are the effects on people of jet leg and shift work?

How can the effects of jet lag be reduced?

How can shift work be made easier to cope with?

Jet Lag
Jet lag occurs when we travel rapidly across time zones.
  • Flying from London to New York takes around 6 hours.
  • If you leave London at noon, you will arrive 6 hours later and your body will feel as though it is 6PM, however it will only be 1PM. Your body will be ready for sleep when it is 7PM locally.
  • This conflict between local time and your biological time leads to tiredness and confusion.

Disruption of the circadian rhythm by jet leg can affect the performance and alertness of business people attending meetings in other countries, air crew, sports players, and so on. Recht, Lew and Schwartz (1995) found that baseball players in the USA won 44% of games when they travelled from the east coast to the west coast, but only won 37% of games when they travelled from the west coast to the east coast. This shows that travelling from east to west is less harmful to the circadian rhythm than travelling from west to east.

Travelling from east to west leads to phase delay of the body clock, which seems easier for the body to cope with than phase advance. Phase delay simply means extending the duration of a rhythm’s cycle (e.g. from 24 hours to 29 hours before returning to 24 hours again), whereas phase advance means shortening the rhythm’s cycle.

Coren (1996) offers advice for minimizing the effect of jet lag:
  • Catch up on sleep before flying to avoid starting with sleep deprivation.
  • During the flight, adopt the daily routine of the destination’s time – e.g. if you are going to arrive at night time then try to sleep on the plane.
  • Adopt the destination’s time (and zeitgebers) as soon as you arrive.
  • Avoid consuming stimulants and depressants such as alcohol and caffeine.
  • If it is morning then expose yourself to as much sunlight as possible in order to reset your biological clock.

Consuming melatonin may help resynchronise the sleep-wake cycle more quickly. Beaumont et al (2004) found that taking melatonin at bed time for 3 days before travel and 5 days after significantly reduced the symptoms of jet lag.


Shift Work
Shift workers are expected to be alert, productive and safe at all times of day and night, however working at night and sleeping during the day is clearly contrary to the normal sleep-wake cycle. The Exon Valdez disaster, Chernobyl nuclear disaster, sinking of the Titanic, and the Piper Alpha disaster are all examples of catastrophes involving shift workers and, although it is not an established fact in these cases, there could well have been an impairment in the performance of workers during the events that caused the disasters.

Artificial lighting makes it possible for humans to be active at nighttime and allows us to work over a full 24-hour period. Factory workers operate heavy machinery, lorry drivers travel long distances, doctors have responsibility for patients’ lives, and air traffic controllers make fast decisions at times when their body clocks (circadian sleep-wake cycles) are completely out of synchronization with the environment. It is therefore vital to understand the effect of working at night and sleeping during the day on safety, productivity and health.

Czeisler et al (1982) found that shift workers at a Utah chemical plant reported high levels of stress, difficulty sleeping, and health problems that affected productivity. The workers were on a backward shift rotation (nights then afternoons then mornings) which was causing their sleep-wake cycles to phase advance (effectively shortening the 24 hour cycle). Czeisler introduced a forward shift rotation (nights then mornings then afternoons) to phase delay the sleep-wake cycle, and placed workers on each shift stage for 21 days to allow the body clock time to fully adjust. After 9 months the workers reported less stress, found sleeping easier, and had increased productivity.

Gordon at al (1986) changed Philadelphia police officers from a backward shift rotation (phase advanced) to a forward shift rotation (phase delayed), with the result that the police officers were more alert and had 40% fewer accidents.

An effective alternative to rotating shift patterns is permanent non-rotating shift work (i.e. always working nights or evenings). Phillips et al (1991) found that when this was introduced for Kentucky police officers, the rate of sleeping at work was lower and they also had fewer accidents. Permanent shifts, however, can lead to other problems as they cause difficulty with social and family life.

Artificial light can have a significant effect on the sleep-wake circadian rhythm. Boivin et al (1996) investigated the power of artificial lighting at resetting biological clock. 31 male subjects were divided into four groups and put on an inverted sleep-wake cycle for three days (to mimic night workers). Each ‘day’ when they awoke they were exposed to five hours of very dim light followed by:
1. Very bright light 10,000 lux
2. Bright light 1260 lux
3. Ordinary room light 180 lux
4. Dim light
After three days the sleep-wake cycles for members of group 1 had advanced five hours earlier, group two by three hours, group 3 one hour and 4 had drifted one hour later. This study shows that even room light can have an effect on circadian rhythms, and has important implications for the type of environment that employers should provide for employees to work in - if a shift worker is to adapt to an inverted sleep-wake cycle quickly, then they should be exposed to very bright light when working at night.

The most effective ways to cope with rotating shift work are:
  • Work a forward rotating shift pattern. This allows the sleep-wake cycle to phase delay, which is easier to cope with than phase advance.
  • Remain on each shift stage for at least one week to allow the body clock to synchronise.
  • Work under bright lights at night and sleep in a dark room during the day. This creates exogenous zeitgebers that reset the body clock.
A Level exam tips
Answering exam questions (PSYA3 AQA A specification)

One thought on “Disruption Of Biological Rhythms Evaluation Essay

Leave a Reply

Your email address will not be published. Required fields are marked *