Disrupting biological rhythms has negative consequences for the individual because this goes against a mainly endogenous, built-in pattern, and so there are physiological and psychological costs of disruption as the body attempts to readjust. 

Seasonal Affective Disorder

One significant disruption is the seasonal change of decreased light during the winter months because this can lead to serious depression in some cases. This condition begins in the autumn as the days shorten and so exposure to light decreases and only tends to lift in the spring as the days lengthen and thus so does light exposure.

RESEARCH EVIDENCE INTO SAD

• Blakemore (1988) reported the case of Pat Moore who had a history of suffering from unipolar depression before she realized that her depression was seasonal. The effect of day light on her mood was tested through exposure to light therapy (phototherapy) for a few hours on waking. The bright white light used was as similar as possible to natural light. Pat showed remarkable improvement within just a few days of beginning therapy.
• Booker and Hellekson (1992) found an incidence of about 9% in Alaska. Alaska lies across the Arctic Circle and so will have very restricted day-length and also low quality of light through the winter months.
• Studies have shown a real benefit of using bright light similar in wavelengths to natural light (Lam et al., 2006, see A2 Level Psychology page 35).
• Avery et al. (1992) have shown light therapy involving dawn simulation is very effective. Light intensity is increased towards the end of the sleeping time, which mimics natural dawn, and reaches a bright light level at the desired waking time

Evaluation of Research

• Applications. The positive improvements on mood for suffers of SAD is immeasurable in terms of their emotional well-being and ability to function and so the research has important applications.
• Generalisability. The case study of Pat Moore is subject to the usual criticism in terms of a lack of generalisability.
• Experimenter expectations/placebo effect. The fact that Pat Moore and the experimenter expected the light therapy to have an effect may explain her improvement and so this may be a placebo effect, i.e. if the improvement is due to expectation and so not the treatment.
• SAD occurs in sunny countries. Feadda et al. (1993) found a similar rate of SAD to that found in the Arctic circle sample in a retrospective study of seasonal mood disorders in Italy, a Mediterranean country known for its sunshine both in summer and most of the winter! There are weaknesses of this research as it was retrospective. If SAD does occur in sunny countries then it may well be that this condition is far more complex than just the amount of natural light.

SHIFT WORK


Shiftwork causes major disruption to the biological rhythms because the individual is working when the body wants to be asleep and trying to sleep when the body wants to be awake. The consequences of this are the same as the symptoms described for jet lag below. If given enough time to adjust, our bodies can reprogram our biological rhythms and thus cope with the shiftwork by reducing disruption. The dangers of shiftwork are illustrated by the industrial accidents at Chernobyl, Bhopal, and Three-Mile Island which all occurred between 1 a.m. and 4 a.m., and the fact that most lorry accidents occur between 4 a.m. and 7 a.m.

RESEARCH EVIDENCE

• Akerstedt (1985) showed that people on shiftwork slept 1–4 hours less than when they could sleep normally at night. He also showed that they had a particular deficit in REM sleep and so if REM sleep has a particular function then this function would also show a deficit.
• Burch et al. (2005) found that night shiftworkers had disrupted circadian melatonin production, and that this was associated with disrupted sleep, fatigue, increased risk of accidents, and even chronic disease.
• Czeisler, Moore-Ede, and Coleman’s “shift rotation” study (1982) found that because phase delay (staying up later) needs less adjustment than phase advance (getting up earlier) it is better to rotate with the clock than against it, i.e. progress from early shift to day shift to night shift, rather than the other way round. Forwards rotation works with rather than against the innate 24.9-hour rhythm. Czeisler et al. tested this in a chemical plant where workers reported feeling better and less tired and managers reported increased productivity and fewer errors. Furthermore, Czeisler found that it was better to have slower shift changes. A pattern of 21 days was therefore better than 7 days, as this provided more time for the workers to adjust, which takes at least 16 days.
• Monk and Folkard’s “types of shiftwork” study (1983, see A2 Level Psychology page 37). They identified two major types of shiftwork: (1) rapid rotation where the worker changes shifts approximately every third shift, and (2) slow rotation where the worker changes shifts every week or month. Both types have strengths and weaknesses, however the rapid rotation seems preferable as it may be possible for the body to maintain a fairly constant circadian rhythm, whereas the slower rotation would cause major disruption.
• The research has been applied positively (Dawson & Campbell, 1991, see A2 Level Psychology page 37). Research findings show that light acts as a zeitgeber in maintaining the rhythm of the SCN. Consequently, bright light has been used as a substitute for sunlight to reset the SCN. Workers exposed to a 4-hour pulse of bright light showed improvements in work performance.
• Research into performance deficits shows the negative impact of shiftwork. Novak et al. (1990, see A2 Level Psychology page 40) studied accident rates in an industrial chemicals plant and found higher accident rates in shiftworkers compared to day workers.
• Further performance deficits relate to car accidents because social data shows that motorway accidents are particularly most likely between 2–4 p.m., midnight to 2 a.m., and 4–6 a.m., and such accidents often involve shiftworkers who have worked for longer than 18 hours. Horne (1992) explains this is due to momentary falling asleep, sometimes for a few seconds only, because an absence of skid or braking marks indicated that the driver had not been aware of the impending accident! This suggests a lapse of consciousness such as when asleep, rather than a lapse of attention.

EVALUATION OF SHIFTWORK

• Negative effects are well-supported. The negative effects of shiftwork are indisputable; the accident record and workers’ self-reports provide clear evidence of the negative consequences of disrupting biological rhythms.
• Face validity. I’m sure you have experienced phase delay yourself and realise it is easier than phase advance, so Czeisler’s findings that it is easier to advance with the clock do make sense.
• Slow or fast rotation? Both have negative consequences. It takes most people about a week to adjust to a new sleep–waking cycle and so fast rotation, approximately every 3 days, would leave workers in a constant state of disruption. But this may be preferable to permanently altering the workers’ circadian rhythms, which slow rotation can do and which may cause lasting harm.
• Applications of the research. The successful use of light is a positive application of research into circadian rhythms.
• Self-report criticisms. Evidence such as Czeisler’s relies on self-report, which of course is not empirical. It is completely subjective because participants’ experiences of shiftwork are not precise and measurable. Furthermore, self-report can be biased by researcher expectancy effects, where the researcher’s expectations cue participants. This can lead to demand characteristics where participants give the answers they think the researcher is looking for.
• Individual differences. The research on circadian rhythms and on the disruption of biological rhythms may lack generalisability because the sleep–wake cycle is subject to individual differences in cycle length and cycle onset. The latter is perhaps particularly significant as the effects of disruption may vary greatly depending on if you are a “lark” (prefer to rise early and go to bed early) or an “owl” (prefer to wake late and go to bed late). Also, some people just cope better with shiftwork than do others and so perhaps these “happy shiftworkers” adapt their biological rhythms more quickly than those who experience more discomfort.
• Correlational criticisms. Cause and effect cannot be established in the relationship between shiftwork and its effects, so we can only say that shiftwork is associated with ill effects rather than that it has caused these effects. Furthermore, the correlation is reductionist because there are other factors that are linked to ill effects and these may be psychological rather than due to biological disruption. For example, there may be less social support for those on shiftwork due to time spent apart from family.

 

Jet Lag Jet lag occurs when the individual crosses time zones because this disrupts the natural rhythm of the biological clock. Thus, jet lag is not caused by the rigours of travelling as is often misperceived. Instead, it only occurs when there is sufficient discrepancy between internal time (your biological clock, which is set to British time) and external time (local time of destination), which only occurs when travelling east to west or west to east, not north to south. The consequences of such disruption are a wide range of symptoms including fatigue, headache, sleep disturbances, irritability, and gastrointestinal disturbances.

RESEARCH EVIDENCE

• Klein, Wegman, and Hunt’s “westbound flights” study (1972, see A2 Level Psychology page 38). Adjustment of the sleep–waking cycle was faster when flying westbound (i.e. going from the UK to the USA) than eastbound, as westbound passengers took 1 day per time zone crossed whereas eastbound passengers took 6 days for complete readjustment, irrespective of whether they were travelling home or away from home.
• Schwartz, Recht, and Lew’s “baseball” study (1995, see A2 Level Psychology page 38). Schwartz et al. analysed the results of American baseball games in relation to whether the teams had to travel east to west or west to east. They found that the west coast teams travelling east lost more games than the east coast teams travelling west. This supports Klein et al.’s (1972) findings that westbound flights are easier to adjust to. However, of course, the ability of the teams studied was also a factor, which wasn’t accounted for!
• Research application (see A2 Level Psychology page 38). Research findings on the circadian rhythm of the sleep–waking cycle have been applied to try to combat the negative effects of disruption. Research revealed the link between melatonin and sleepiness and so melatonin tablets have been tested as a cure for jet lag.
• Cho (2001, see A2 Level Psychology page 39) found a reduction in temporal lobe size and memory function in air crew who regularly flew over seven time zones, especially if only a short turn-around time was allowed. This challenges the view that jet lag is psychological, as it shows organic structural changes and cognitive reduction in the disorder.
• Stewart and Amir (1998, see A2 Level Psychology page 38) found that rats that have been emotionally upset are not as good at resetting their innate clocks using light as the zeitgeber as rats that have not been emotionally stressed. Thus, they suggested that emotional upsets could make the SCN less responsive to light. This could be a factor in humans as well, and could explain why some people experience significant jet lag and others do not seem to—those who do may experience flying and travel as more stressful than those who don’t.

EVALUATION

• Phase advance vs. phase delay. The research finding that westbound flights require less adjustment than eastbound ones is supported and explained by the fact that when travelling west the day is lengthened and when travelling east it is shortened. It is easier to stay up late (phase delay) than get up early (phase advance). This is because the natural rhythm of the biological clock is almost 25 hours and so it is easier to adapt to beyond 24 hours than to less than 24 hours.
• Face validity. It does make sense that it is easier to stay up late than get up early; most of us know that it is far easier to stay up late at night and feel fine at the time than it is to wake up even one hour earlier in the morning and feel fine. Thus, the research has face validity, i.e. it makes sense.
• Applications. Melatonin is being developed as a treatment. Anecdotal reports suggest it can be useful in resetting the endogenous clock if small doses are taken a couple of hours before local bedtime. Clearly anecdotal evidence is not very scientific and so this is a key weakness of the research to date.

 
SO WHAT DOES THIS MEAN? The biological rhythms are determined primarily by endogenous factors but these interact with exogenous factors, and physiology (the endogenous factors) can be overridden, e.g. shiftwork. Disrupting biological rhythms can have short- and long-term effects, e.g. jet travel is a temporary disruption and so although readjustment can be extremely uncomfortable it has no long-term effects. Shiftwork is a more permanent disruption experienced by many and the consequences of this can be long lasting. The negative effects can be reduced and so it is important to consider the speed and direction of the rotation.

past exam questions

• June 2011 – Consider the consequences of disrupting biological rhythms (16 marks)
• June 2013 – Discuss research into the disruption of biological rhythms (eg shift work, jet lag) (8 + 16 marks)

teaching ideas

•   Powerpoint presentation to go through it all, explain the basics, studies and evaluations.
  
•  Group Task - Present to class a talk through, and evaluation of a study talked about previously.
  
•  Work as a class to devise an essay plan for past exam question.  Further enforces subject content and practices exam techniques such as exam structure and effective evaluation required for longer essay questions.