Biological rhythms (circadian rhythms)

Question 1

What is meant by biological rhythms?

Answer 1

Biological rhythms - All living organisms are subject to biological rhythms and they influence how our body systems behave
These biological rhythms are governed by two things:
1. Endogenous pacemakers - the body’s internal biological clocks
2. Exogenous zeitgebers - external changes in the environment

Question 2

What 2 things are biological rhythms governed by?

Answer 2

Endogenous pacemakers and exogenous Zeitgebers

Question 3

Name an important exogenous Zeitgeber

Answer 3

The effects of day and light - we feel sleepy when its night time and awake during the day

Question 4

The sleep/wake cycle is governed by what?

Answer 4

An internal endogenous pace maker (a biological clock called the suprachiasmatic nucleas - SCN)

Question 5

What was the procedure of Siffre’s cave study?

Answer 5

Michel Siffre spent serveral extended periods underground to study the effects on his own biological rhythms
He had no exposure to natural light or sound, only access to adequate food and drink
He recorded his vitals each day with limited access to human communication

Question 6

What were Siffre’s cave study findings?

Answer 6

Found that he fell into a cycle, but it repeated every 25 hours rather than the usual 24

Question 7

What were Siffre’s cave study conclusions?

Answer 7

From this study we can conclude that circadian rhythms are primarily regulated by an internal ‘body clock’ (endogenous pace maker) but are synchronised to the normal 24 hour day by external cues (exogenous zeitgebers) like sunlight. Without the influence of external zeitgebers it naturally settles into a 25-hour pattern.

Question 8

What was Aschoff and Wevers procedure?

Answer 8

Group of participants spent 4 weeks in a WW2 bunker with no natural light
All but one of the participants displayed a circadian rhythm between 24 and 25 hours

Question 9

What was Folkards procedure?

Answer 9

12 people agreed to live in a dark cave for 3 weeks
Going to ‘bed’ when the clocks said 11:45pm and then ‘rising’ when the clock said 7:45am
Over the 3 weeks, the researchers secretly sped up the clock so that it ran for 22 hours (rather than 24)
Only one of the participants was able to adjust to the new timings
This suggests the existence of a strong free-running circadian rhythm cannot easily be overridden by exogenous zeitgebers

Question 10

Why is our sleep/wake cycle 24 hours and not 25?

Answer 10

The sleep/ wake cycle should be 25 hours, but due to environmental cues (eg. light) our 25 hour cycle is syncronised with the 24 hour day

Question 11

Give an overview of how core body temp changes throughout the day

Answer 11

Body temperature is lowest when you are asleep at 4am
It gradually rises again
There is a slight body temperature drop after lunch
At around 6pm, your body temperature rises again and peaks
When your body temperature is lower, you feel more tired

Question 12

What was Folkards research regarding core body temperature?

Answer 12

His research showed that children who had stories read to them at 3pm showed much better recall and comprehension after a week, compared to the same children who heard the same story at 9am

Question 13

What was Guptas research regarding core body temperature?

Answer 13

Their research found that participants got better scores on IQ tests when they were assessed at 7pm, compared to those who were assessed at 2pm and 9am
Therefore: The warmer we are internally, the better our cognitive performance is

Question 14

Give 2 strengths of 24/25 hour cycle

Answer 14

1. Shift work - Gives people an understanding of what happens as a consequence of circadian rhythms being disrupted (desychronisation)
   Night workers experience a period of reduced concentration around 6am (a circadian trough) - this means that mistakes/ accidents are more likely to happen then
   Research has also been done on shift workers and poor health - shift workers are 3 times more likely to develop heart disease than people who work ‘normal’ shift patterns
   The sleep/wake cycle may have real-world economic implications in terms of how best to manage worker productivity
2. Medical treatment - Circadian rhythms co-ordinate many of the body’s basic processes - hormone level, heart rate and digestion
   These all rise and fall during the day which has lead chronotherapeutics
   This is how medical treatment can be administered in line with a person’s biological rhythm
   For example, Bonten et al (2015) found that Aspirin (treatment for heart attacks) is most effective if its taken at night as heart attacks are most likely to happen early in the morning
   This shows that circadian rhythm research can help increase the effectiveness of drug treatment

Question 15

Give 2 limitations of 24/25 hour cycle

Answer 15

1. Shift work counter point - Shift worker research looks at correlation methods - because of this its difficult to know whether desynchronisation of the sleep/wake cycle is actually a cause of the negative effects
   Charlene soloman (1993) concluded that the higher divorce rate in shift workers could be due to the strain of deprived sleep and other influences such as missing out on important familu
2. Individual differences - The studies into circadian rhythms (Siffre, Aschoff) are based on very small samples of participants
   More research has shown that the sleep/wake cycle varies widely
   Charles Czeisler et al (1999) found that individual differences in sleep/wake cycles varied from 13 hours to 65 hours
   Duffy et al (2001) found that there were some people who had a natural preference for going to bed early and rising early (known as ‘larks’) and those who were the opposite (‘owls’)
   Siffre (1999) also found that his own sleep/wake cycle slowed down as he got older
   Therefore, the research data can only be used to discuss averages which could be meaningless

Question 16

Give information on ‘moving the school day’

Answer 16

Wolfson and Carskadon (1998) recommended that the school day should start a few hours later to fit in with the typical teenage chronotype (sleep pattern)
Hormonal shifts in teenagers means that getting to sleep becomes more difficult and because of this they are sleepier at the start of the day
Research has shown benefits for academic and behavioral performance when lessons start later in the day - it also reduces the dependence on caffiene
However:
* This is disruptive for teachers and parents
* Would reduce the number of extra curricular activities
* Probably wouldn’t reduce sleep deprivation as the teenagers would probably stay up later