6.7: Exogenous zeitgebers and the sleep/wake cycle

Question 1

Evaluation:
Strengths:
1. The influence of exogenous zeitgebers may be overstated.
Miles et al. recount the story of a young man, blind from birth, with a circadian rhythm of 24.9 hours.
Despite exposure to social cues, his sleep/wake cycle could not be adjusted and consequently, he had to take sedatives at night and stimulants in the morning to keep pace with the 24 hour world.
Similarly, studies of individuals who live in Arctic regions (where the Sun does not set during the summer months) show normal sleep patterns despite the prolonged exposure to light.
Both of these examples suggest that there are occasions where exogenous zeitgebers may have little bearing on out internal rhythm.

2. Methodological issues in studies.
   The findings from Campbell and Murphy’s study have yet to be replicated.
   Other psychologists have been critical of the manner in which the study was conducted and have suggested that there may have been some limited light exposure to the participants’ eyes - a major confounding variable.
   As well as this, isolating one exogenous zeitgeber (light) in this way does not give us insight into the many other zeitgebers that influence the sleep/wake cycle and the extent to which these may interact.
3. Interactionist system.
   Only in exceptional circumstances are endogenous pacemakers free-running and unaffected by the influence of exogenous zeitgebers.
   Total isolation studies, such as Siffre’s case study, are extremely rate and could be judged as lacking validity for this reason.
   In real life, pacemakers and zeitgebers interact and it may make little sense to separate the two for the purpose of research

Answer 1

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Question 2

There are unpleasant and potentially dangerous effects of shift work on the body’s biological clock.
Jet lag is another important form of desynchronisation that can disrupt what?

Answer 2

Jet lag is another important form of desynchronisation that can disrupt the sleep/wake cycle

Question 3

There are unpleasant and potentially dangerous effects of shift work on the body’s biological clock.
Jet lag is another important form of desynchronisation that can disrupt the sleep/wake cycle, causing sleeplessness, irritability and nausea, as what?

Answer 3

Jet lag is another important form of desynchronisation that can disrupt the sleep/wake cycle, causing:
1. Sleeplessness
2. Irritability
3. Nausea
,as the body struggles to adapt to changing time zones

Question 4

Normally, the body uses cues to from its processes and from the environment, such as what, to keep the various rhythms on track?

Answer 4

Normally, the body uses cues to from its processes and from the environment, such as:
1. The clock time
2. Social activities
3. The light/dark cycle
4. Meal times
to keep the various rhythms on track

Question 5

Normally, the body uses cues to from its processes and from the environment, such as the clock time, social activities, the light/dark cycle and meal times to keep the various rhythms on track.
Example

Answer 5

For example, body temperature is highest during the afternoon and early evening (6pm) and lowest in the early morning (4am or just before sunrise)

Question 6

Normally, the body uses cues to from its processes and from the environment, such as the clock time, social activities, the light/dark cycle and meal times to keep the various rhythms on track.
For example, body temperature is highest during the afternoon and early evening (6pm) and lowest in the early morning (4am or just before sunrise).
However, if the person is working at night, what?

Answer 6

However, if the person is working at night, the body temperature does not have as much variation during a 24 hour period as it would normally

Question 7

Normally, the body uses cues to from its processes and from the environment, such as the clock time, social activities, the light/dark cycle and meal times to keep the various rhythms on track.
For example, body temperature is highest during the afternoon and early evening (6pm) and lowest in the early morning (4am or just before sunrise).
However, if the person is working at night, the body temperature does not have as much variation during a 24 hour period as it would normally.
The temperature rhythm and other body rhythms get out of sync.
What do these rhythms also do?

Answer 7

These rhythms also get out of phase with the person’s activity pattern

Question 8

Normally, the body uses cues to from its processes and from the environment, such as the clock time, social activities, the light/dark cycle and meal times to keep the various rhythms on track.
For example, body temperature is highest during the afternoon and early evening (6pm) and lowest in the early morning (4am or just before sunrise).
However, if the person is working at night, the body temperature does not have as much variation during a 24 hour period as it would normally.
The temperature rhythm and other body rhythms get out of sync.
These rhythms also get out of phase with the person’s activity pattern.
What can this lead to?

Answer 8

This can lead to feelings of fatigue and disorientation

Question 9

Normally, the body uses cues to from its processes and from the environment, such as the clock time, social activities, the light/dark cycle and meal times to keep the various rhythms on track.
For example, body temperature is highest during the afternoon and early evening (6pm) and lowest in the early morning (4am or just before sunrise).
However, if the person is working at night, the body temperature does not have as much variation during a 24 hour period as it would normally.
The temperature rhythm and other body rhythms get out of sync.
These rhythms also get out of phase with the person’s activity pattern.
This can lead to feelings of fatigue and disorientation.
What is a term often used to describe these feelings?

Answer 9

Jet lag is a term often used to describe these feelings

Question 10

Normally, the body uses cues to from its processes and from the environment, such as the clock time, social activities, the light/dark cycle and meal times to keep the various rhythms on track.
For example, body temperature is highest during the afternoon and early evening (6pm) and lowest in the early morning (4am or just before sunrise).
However, if the person is working at night, the body temperature does not have as much variation during a 24 hour period as it would normally.
The temperature rhythm and other body rhythms get out of sync.
These rhythms also get out of phase with the person’s activity pattern.
This can lead to feelings of fatigue and disorientation.
Jet lag is a term often used to describe these feelings.
Some rhythms adapt in 2 - 3 days, whilst others what?

Answer 10

Some rhythms adapt in 2 - 3 days, whilst others change only after longer periods

Question 11

Normally, the body uses cues to from its processes and from the environment, such as the clock time, social activities, the light/dark cycle and meal times to keep the various rhythms on track.
For example, body temperature is highest during the afternoon and early evening (6pm) and lowest in the early morning (4am or just before sunrise).
However, if the person is working at night, the body temperature does not have as much variation during a 24 hour period as it would normally.
The temperature rhythm and other body rhythms get out of sync.
These rhythms also get out of phase with the person’s activity pattern.
This can lead to feelings of fatigue and disorientation.
Jet lag is a term often used to describe these feelings.
Some rhythms adapt in 2 - 3 days, whilst others change only after longer periods.
People adapt to new schedules at different rates as do what?

Answer 11

People adapt to new schedules at different rates as do the different rhythms

Question 12

Normally, the body uses cues to from its processes and from the environment, such as the clock time, social activities, the light/dark cycle and meal times to keep the various rhythms on track.
For example, body temperature is highest during the afternoon and early evening (6pm) and lowest in the early morning (4am or just before sunrise).
However, if the person is working at night, the body temperature does not have as much variation during a 24 hour period as it would normally.
The temperature rhythm and other body rhythms get out of sync.
These rhythms also get out of phase with the person’s activity pattern.
This can lead to feelings of fatigue and disorientation.
Jet lag is a term often used to describe these feelings.
Some rhythms adapt in 2 - 3 days, whilst others change only after longer periods.
People adapt to new schedules at different rates as do the different rhythms.
Why may total reversal of circadian rhythms never occur?

Answer 12

Total reversal of circadian rhythms may never occur, because on days off, most people go back to a ‘normal’ day schedule

Question 13

Normally, the body uses cues to from its processes and from the environment, such as the clock time, social activities, the light/dark cycle and meal times to keep the various rhythms on track.
For example, body temperature is highest during the afternoon and early evening (6pm) and lowest in the early morning (4am or just before sunrise).
However, if the person is working at night, the body temperature does not have as much variation during a 24 hour period as it would normally.
The temperature rhythm and other body rhythms get out of sync.
These rhythms also get out of phase with the person’s activity pattern.
This can lead to feelings of fatigue and disorientation.
Jet lag is a term often used to describe these feelings.
Some rhythms adapt in 2 - 3 days, whilst others change only after longer periods.
People adapt to new schedules at different rates as do the different rhythms.
Total reversal of circadian rhythms may never occur, because on days off, most people go back to a ‘normal’ day schedule.
What can frequent changes in schedule and disruption to circadian rhythms lead to?

Answer 13

Frequent changes in schedule and disruption to circadian rhythms can lead to chronic fatigue and other health problems

Question 14

When does jet lag occur?

Answer 14

Jet lag occurs when we travel rapidly across time zones

Question 15

Jet lag occurs when we travel rapidly across time zones.

Flying from London to New York takes how long?

Answer 15

Flying from London to New York takes around 6 hours

Question 16

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 12pm, what?

Answer 16

If you leave London at 12pm, you will arrive 6 hours later and your body will feel as though it is 6pm, but it will only be 1pm

Question 17

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 12pm, you will arrive 6 hours later and your body will feel as though it is 6pm, but it will only be 1pm.
When will your body be ready for sleep?

Answer 17

Your body will be ready for sleep when it is 7pm locally

Question 18

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 12pm, you will arrive 6 hours later and your body will feel as though it is 6pm, but it will only be 1pm.
Your body will be ready for sleep when it is 7pm locally.
What does this conflict between local time and your biological time lead to?

Answer 18

This conflict between local time and your biological time leads to tiredness and confusion

Question 19

Disruption of the circadian rhythm by jet lag can affect the what of business people attending meetings in other countries, air crew, sports players, ect?

Answer 19

Disruption of the circadian rhythm by jet lag can affect the performance and alertness of business people attending meetings in other countries, air crew, sports players, ect

Question 20

Disruption of the circadian rhythm by jet lag can affect the performance and alertness of business people attending meetings in other countries, air crew, sports players, ect.
For example, 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.

What does travelling from east to west lead to?

Answer 20

Travelling from east to west leads to phase delay of the body clock

Question 21

Disruption of the circadian rhythm by jet lag can affect the performance and alertness of business people attending meetings in other countries, air crew, sports players, ect.
For example, 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 what?

Answer 21

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

Question 22

Disruption of the circadian rhythm by jet lag can affect the performance and alertness of business people attending meetings in other countries, air crew, sports players, ect.
For example, 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.
What does phase delay simply mean?

Answer 22

Phase delay simply means extending the duration of a rhythm’s cycle (for example, for 24 hours to 29 hours before returning to 24 hours again)

Question 23

Disruption of the circadian rhythm by jet lag can affect the performance and alertness of business people attending meetings in other countries, air crew, sports players, ect.
For example, 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 (for example, for 24 hours to 29 hours before returning to 24 hours again), whereas what does phase advance mean?

Answer 23

Phase delay simply means extending the duration of a rhythm’s cycle (for example, for 24 hours to 29 hours before returning to 24 hours again), whereas phase advance means shortening the rhythm’s cycle

Question 24

What does the German word zeitgeber mean?

Answer 24

The German word zeitgeber means ‘time giver’

Question 25

Exogenous zeitgebers

Answer 25

Exogenous zeitgebers are external cues that may affect or entrain our biological rhythms, such as the influence of light on the sleep/wake cycle, temperature and social cues

Question 26

The German word zeitgeber means ‘time giver.’

Exogenous zeitgebers are external factors in the environment that do what?

Answer 26

Exogenous zeitgebers are external factors in the environment that reset our biological clocks through a process known as entrainment

Question 27

Exogenous zeitgebers are external factors in the environment that reset our biological clocks through a process known as entrainment.
In the absence of external cues, the free running biological clock that that controls the sleep/wake cycle continues to ‘tick’ in a distinct cyclical pattern (as in the Siffre study).
Thus, what?

Answer 27

Thus, sleeping and wakefulness would seem to be determined by an interaction of internal and external factors

Question 28

What is a key zeitgeber in humans?

Answer 28

Light is a key zeitgeber in humans

Question 29

Light is a key zeitgeber in humans.

What can it do?

Answer 29

It can reset the body’s main endogenous pacemaker, the SCN

Question 30

Light is a key zeitgeber in humans.

It can reset the body’s main endogenous pacemaker, the SCN, and thus plays a role in what?

Answer 30

It can reset the body’s main endogenous pacemaker, the SCN, and thus plays a role in maintenance of the sleep/wake cycle

Question 31

Light is a key zeitgeber in humans.
It can reset the body’s main endogenous pacemaker, the SCN, and thus plays a role in maintenance of the sleep/wake cycle.
What does light also have an indirect influence on?

Answer 31

Light also has an indirect influence on key processes in the body that control functions such as hormone secretion and blood circulation

Question 32

As every parent knows, infants are seldom (rarely, not often) what?

Answer 32

As every parent knows, infants are seldom (rarely, not often) on the same sleep/wake cycle as the rest of the family

Question 33

As every parent knows, infants are seldom (rarely, not often) on the same sleep/wake cycle as the rest of the family.
In human infants, what is the initial sleep/wake cycle?

Answer 33

In human infants, the initial sleep/wake cycle is pretty much random

Question 34

As every parent knows, infants are seldom (rarely, not often) on the same sleep/wake cycle as the rest of the family.
In human infants, the initial sleep/wake cycle is pretty much random.
At about 6 weeks of age, what happens?

Answer 34

At about 6 weeks of age, the circadian rhythms begin

Question 35

As every parent knows, infants are seldom (rarely, not often) on the same sleep/wake cycle as the rest of the family.
In human infants, the initial sleep/wake cycle is pretty much random.
At about 6 weeks of age, the circadian rhythms begin and by about 16 weeks, what?

Answer 35

At about 6 weeks of age, the circadian rhythms begin and by about 16 weeks, most babies are entrained

Question 36

As every parent knows, infants are seldom (rarely, not often) on the same sleep/wake cycle as the rest of the family.
In human infants, the initial sleep/wake cycle is pretty much random.
At about 6 weeks of age, the circadian rhythms begin and by about 16 weeks, most babies are entrained.
What are likely to be a key influence here?

Answer 36

The schedules imposed by parents are likely to be a key influence here

Question 37

As every parent knows, infants are seldom (rarely, not often) on the same sleep/wake cycle as the rest of the family.
In human infants, the initial sleep/wake cycle is pretty much random.
At about 6 weeks of age, the circadian rhythms begin and by about 16 weeks, most babies are entrained.
The schedules imposed by parents are likely to be a key influence here, including what?

Answer 37

The schedules imposed by parents are likely to be a key influence here, including adult-determined mealtimes and bedtimes

Question 38

As every parent knows, infants are seldom (rarely, not often) on the same sleep/wake cycle as the rest of the family.
In human infants, the initial sleep/wake cycle is pretty much random.
At about 6 weeks of age, the circadian rhythms begin and by about 16 weeks, most babies are entrained.
The schedules imposed by parents are likely to be a key influence here, including adult-determined mealtimes and bedtimes.
What does research also suggest?

Answer 38

Research also suggests that adapting to local times for eating and sleeping, rather than responding to one’s own feelings of hunger and fatigue, is an effective way of entraining circadian rhythms and beating jet lag when travelling long distances

Question 39

Exogenous zeitgebers help regulate the body clock, so that the individual is synchronised with the environment.
What are examples of exogenous zeitgebers?

Answer 39

Examples of exogenous zeitgebers are:

1. Sunlight
2. Noise
3. The seasons
4. The moon

Question 40

Entrainment

Answer 40

Entrainment is where there is an adjustment of the body clock in line with the environment

Question 41

Entrainment is where there is an adjustment of the body clock in line with the environment.
This happens when a traveller crosses time zones, as what?

Answer 41

This happens when a traveller crosses time zones, as their pacemakers are not synchronised with the environment anymore

Question 42

Entrainment is where there is an adjustment of the body clock in line with the environment.
This happens when a traveller crosses time zones, as their pacemakers are not synchronised with the environment anymore.
What do zeitgebers therefore do?

Answer 42

Zeitgebers therefore act as cues, allowing the person to adjust

Question 43

The interactionist theory is that it is reductionist to

Answer 43

The interactionist theory is that it is reductionist to say fully endogenous or exogenous

Question 44

The interactionist theory is that it is reductionist to say fully endogenous or exogenous.
What is likely?

Answer 44

It is likely that the endogenous rhythm is free-running, but entrained by external factors