Psychology A2
Biological Rhythms
Key Issues
 What is a biological Rhythm?
 What behaviours change under the influence of such
rhythms?
 How do endogenous (internal) and exogenous(external)
factors interact to control cycles?
 What consequences can arise from disturbances to daily
rhythms such as shift work and jet lag?
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Lots of behaviours occur regularly in cycles. These rhythms
may be of different lengths.
Ultradian - Occurs more than once a day. E.g. eating
Circadian – Occurs approx. every 24 hours. E.g.
Sleep-Wake cycle
Infradian – Occurs more than every 24 hours and
less than yearly. E.g. menstrual cycle
Circannual – Occurs approx. yearly. E.g. the hibernation cycle
in animals
What type of bodily rhythms are these?
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The sleep-wake cycle
Eating
Hibernation
Body temperature
Menstrual cycle
Seasonal Affective disorder
Migration in birds
Dream cycles
Heartbeats
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What determines the length of these rhythms??
 A combination of biological, environmental, social and
cultural factors
 Body Size
 Age
 Lifestyle
There are clearly individual differences in Biological Rhythms!
Here are some things to try at home to test them!
 In built stopwatch
 Owls or larks?
Built in stopwatch – experiment
Sometimes it seems as if time flies by………sometimes it drags
on forever. How good are you estimating time? Do you have a
built in stopwatch?
Estimate the length of a period of time, e.g. one minute. Tell
your ppt to count to 60 by ones at a rate of one per second.
When say “GO” start your timer. When your ppt gets to 60,
stop the timer. How close was your ppt?
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Are you a Lark or an Owl?????
1.) What time would you get up if you were entirely free
to plan your day?
a) Before 7am
b) 7-9 am.
c) after 9am
2.) How easy is it for you to get up on work days?
a) Very difficult
b) Moderately difficult/depends on the day
c) Fairly easy
3.) How alert do you feel during the first 30 minutes after
you get up in the morning?
a) Alert/fresh
b) Varies
c) Sleepy/tired
4.) What time would you go to bed if it were completely up to you?
a) After midnight
b) 10.30pm-midnight
c) before 10.30pm
5.) How sleepy/tired are you 1½ hours before going to bed
during the work week?
a) Very tired/ready to fall asleep
b) Not very tired
c )Moderately tired/depends on the day
6.) When you’ve stayed up later than usual (had a late evening),
when do you wake up the next morning (assuming you didn’t
have any alcohol)?
a) Varies
b) At your usual time with a desire to get out of bed
c) Later than usual, with a desire to fall back asleep
Now add up your score:
Question A
B
1
1
2
2
3
2
3
1
2
4
3
2
5
1
3
6
2
1
My total =
6-8 Extreme Lark
8-10 Lark
10-14 Hummingbird
14-16 Owl
16-18 Extreme owl
C
3
1
3
1
2
3
Owls often skip breakfast, and they're always
rushing to get to work in the morning. If you're
an owl, you'd struggle to be a milkman. Most
college students and 20-somethings are owls.
They need multiple alarm clocks to get up in
the morning!
Hummingbirds are somewhere in the middle
between larks and owls. You’re one of the
lucky ones – you can occasionally get up early
to get things done, but are also in your element
at an all night party!
Larks rarely nap, and prefer to exercise in the
morning. They are most productive late
morning, and go to sleep on average 2 hours
before owls, falling asleep faster. If you’re a
lark, you wouldn’t enjoy a job as a night-time
bartender.
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Endogenous and Exogenous rhythms
Where control of biological rhythms is exerted from within –
they are referred to as pacemakers and are endongenous.
N
E
dogneous
-P
acemaker
Where control is exerted from outside by exogenous
environmental stimuli, they are known as zeitgebers.
X
e
ogneous
-Z
eitgeber
How are Circadian Rhythms influenced by
endogenous pacemakers and exogenous
zeitgebers?
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The pineal gland secretes the hormone melatonin in inverse
proportion to the light.
Increase in melatonin is associated with sleep
The SCN is responsible for the release for melatonin
In animals, the pineal gland activates the release of melatonin
In humans, the light from the retina goes to the SCN to the pineal
gland which releases the melatonin.
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Light, endogenous pacemakers and sleep
The SCN and pineal gland
In birds (and reptiles), light is sensed through the
thin layer of cranial bone.
This stimulates the pineal gland
The pineal gland has its own pacemaker activity, but
the incoming light (or lack of) leads to changes in the
amount of melatonin being produced.
different
Humans have a
clock – the SCN
(Suprachiasmic nuclei)
Light enters through the eyes and some of the optic nerve
fibres create a tract to the SCN (which is in the
hypothalamus)
This is the human/mammalian alternative to pineal gland
stimulation.
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Evidence for the role of the SCN playing a part in melatonin release
comes from two places:
If you electrically stimulate the SCN in rats, this can modify their body
clock . Also Lesions in the SCN abolish the night-day cycle.
The role of Melatonin
Label the diagram with:
 Where the eye is
 The path of the light to the pineal gland
 Where serotonin is changed into melatonin
 The path of melatonin
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The SCN pineal gland
What is the role of the pineal gland?
How does it work?
The pineal gland is both an endogenous pacemaker and also
linked with external factors. How is this?
Whereabouts is the main clock located in humans?
Explain why the SCN was crucial for the survival of the
DeCoursey et al 2000 chipmunks.
Explain why “Night time Milk” (high in melatonin)
helps people to sleep.
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How reliable is our internal body clock?
The Cave study: Michel Siffre (1972)
Aim: This study investigated what would happen to people’s circadian rhythms if
they were cut off from all zeitgebers (signals from outside the body that tell us about
the time of day – such as light and dark, clocks), and had to rely on their endogenous
pacemaker (internal body clock) to tell them when to eat and sleep. Would we still
stick to a natural 24-hour rhythm?
Method: Michel Siffre, a French cave explorer, spent over six months living in a cave
in Texas, deep under the ground, with no light, or anything else to tell him what time
of day it was. His biological clock was allowed to ‘free-run’, that is, he just followed
his body’s inclinations, eating and sleeping whenever he chose, with no fixed
timetable. He was wired up so that some of his body functions could be recorded; he
had a telephone link to the outside world, and was monitored by video camera.
Results: Siffre had a fairly erratic sleep-wake pattern at first, but it settled down to a
pattern that averaged just over 25 hours, instead of 24 hours.
Conclusion: We do have an internal mechanism that regulates our sleep/wake cycle,
but it shifts to a length of approximately 25 hours if we do not have external
zeitgebers to reset it.
Evaluation: This is a one-participant study, so may not be generalisable to all
humans. Also Siffre’s living conditions were unusual in other ways than simply
lacking time signals, and other factors such as loneliness could have affected his
behaviour.
Similar studies have been done with rats, isolating them from daylight (Groblewski),
and found a similar increase in the sleep-wake cycle, which supports the findings
from the Siffre study. A strength of the study is that it lasted a long time, allowing
Siffre’s rhythms to settle down into a natural pattern.
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Research
Methodological Ethical
weakness
issue
Positive
point
Siffre’s cave
study
Morgan’s
‘hamster
studies’
Miles et al’s
study of a blind
man
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Infradian Rhythms (longer than one day)
Some are synchronised to the waxing and waning of the moon that forms
a lunar month (29.5days).
The most common Infradian Rhythm is the female menstrual cycle and
other reproductive cycles. It is generated by the hypothalamus.
Fluctuations in hormone level affect internal biology and (ovulation and
menstruation) and sexual behaviour.
The average cycle is 29.5 days, although this varies between individual
women. Blocking out the moon and the use of artificial light affects the
timing of the cycle but without these artificial clues it returns to 29.5days.
(Binkley, (1997)
Activity : Write a description and evaluation
below for each of the following studies: Russell et al’s female pheromones study
 Reinberg’s study on menstruation in the
absence of zeitgebers.
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Russell et al
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Reinberg
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Circannual rhythms (once a year)
Hibernation and migration and examples of
circannual rhythms in the animal world
Research has revealed circannual changes in
humans including: mental health
 testosterone production
 white blood cell function
 blood pressure
 secretion of cortisol
What are the implications of the above to a
person’s general health?
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What is SAD?
SAD (Seasonal Affective Disorder) is a type of winter depression
which affects millions of people every winter between September
and April, in particular during December, January and February.
SAD is caused by a biochemical imbalance in the hypothalamus due
to the shortening of daylight hours and the lack of sunlight in winter.
For many people SAD is a seriously disabling illness, preventing them from
functioning normally without continuous medical treatment. For others, it is a milder
condition.
Symptoms
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a desire to oversleep and difficulty staying awake, but in some cases, disturbed
sleep and early morning wakening;
feeling fatigue and an inability to carry out normal routine;
a craving for carbohydrates and sweet foods, usually resulting in weight gain;
feelings of misery, guilt and loss of self-esteem, sometimes hopelessness and
despair, sometimes apathy and loss of feelings;
an irritability and desire to avoid social contact;
a tension and inability to tolerate stress;
a decreased interest in sex and physical contact
SAD symptoms usually reoccur regularly each winter, starting between September
and November and continuing until March or April; a diagnosis can be made after 2
or more consecutive winters of symptoms.
SAD symptoms disappear in spring, either suddenly with a few weeks of
hypomania/hyperactivity, or gradually, depending on the intensity of sunlight in the
spring/early summer.
SAD may begin at any age, but the main age of onset is 18-30. It occurs throughout
the northern and southern hemispheres but is rare in those living within 30 degrees of
the Equator, where daylight hours are long, constant and extremely bright.
What type of rhythm is SAD an example of?
Do internal or external cues affect SAD? Explain
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Mini - assignments for biological
rhythms
1. Outline what we mean by an endogenous pacemaker
2. What is the name given to external events that play a role in rhythmic
activities? Give an example
3. Name four types of biological rhythm, describe each one briefly, and give
an example of each
4. Prepare an outline (in 150 words) of seasonal affective disorder
5. Name and describe two brain structures with important roles as biological
clocks
6. What hormone is involved in regulating our biological rhythms? Where is it
released from?
7. Write a 150-word précis of the findings of 2 studies of free-running
biological rhythms and what they can tell us about the control of biological
rhythms
8. Identify and give a brief account of two critical (AO2) points relating to
studies of free-running biological rhythms
9. Outline in 100 words two examples of the disruption of biological rhythms in
everyday life and their effects on behaviour
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Disrupting Biological Rhythms
The specification requires you to know the consequences of disrupting
rhythms. We are going to look at jet lag & shift work
The best example of how biological rhythms can be disrupted and one
that is frequently encountered, is Jet Lag. If you leave the UK at 10am
and fly to New York your body clock tells you it is 4pm. However, it is
actually 11pm because of the different time zone. This would mean that
around 5pm your body would be telling you it is bed time. Apart from
light, what other zeitgebers might affect you,telling you it is not??
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What symptoms are common when you are suffering jet lag?
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Research has shown that jet leg is worse when you travel west
to east rather than east to west.
Explain why this might be
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Shift Work
Shift work involves a working pattern that allows factories and
organisations to work around the clock. 24/7. This involves people
working when their body clock is telling them to sleep, causing a major
disruption to their biological rhythms.
Shift Work – this involves trying to disobey our ‘internal clock’ . The
consequences are still not completely known but what is known is the
amount of accidents blamed of the effects of incorrect decisions made
as a result of lack of sleep. These include: The challenger space disaster
 Chernoble
 Exxon Valdez oil spill.
Explain what Stevens found about the effect of artificial lighting on
biological rhythms.
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Explain what Cho et al found out about Female Flight attendants
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Bodily rhythms - Recap
There are three main types of bodily rhythm. The first is the
___________ bodily rhythm, which has a cycle of less than a day. Two
examples of this are ___________ and ___________. Cycles that are
approximately a day in length are known as ___________ rhythms. Even
when external cues are removed, there is evidence for a __________________ cycle, as shown by studies where light is removed.
However, this can be shorter or longer than 24 hours, depending on the
_______ of animal it is. This is evidence for an internal “clock”, known
as an ____________.
The final type of bodily rhythm is one that lasts for longer than a day, and
this is known as an ____________ rhythm. An example of this are the
menstrual cycle. If an infradian cycle lasts longer approximately a year,
such as in the case of hibernation or migration, then this can also be
known as a ____________ rhythm. A lot of research has suggested that
seasons of the year can affect this, as in the case of ________, a condition
where lack of light can lead to depression. The light affects the
___________ (part of the brain).
There seems to be a common trend in bodily rhythms amongst
individuals, but also slight individual differences (e.g. the lark/owl effect,
a term coined by ___________(1985).
There is evidence to suggest that bodily rhythms are independent of each
other - __________ et al (1981) found that when ________ monkeys had
damage to their sleep-wake cycle, their temperature cycles were not
affected. However, we need to do more research into humans, as we
cannot ____________ from animal findings to humans.
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