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Unit 4 Bio Rhthyms 1
Physiological Psychology
Biological Rhythms
Unit 4 Bio Rhthyms 2
Unit 4 Bio Rhthyms 3
What is a bio-rhythm?Which of the following diagrams would you consider to be showing a rhythmic pattern?
Unit 4 Bio Rhthyms 4
What is a biological rhythm?
• A periodic change in the behaviour or physiology of animals and plants – (eg sleep, hibernation
and migration)
• People that study biological rhythms are known as ‘chronobiologists’
Unit 4 Bio Rhthyms 5
The Main Bio-Rhythms
1 Ultradian Rhythm
(less than 24 hours)
2 Circadian Rhythm
(24 hours)
3 Infradian Rhythm
(1 month)
4 Circannual Rhythms
(1 year)
Unit 4 Bio Rhthyms 6
The Circadian Rhythm
A daily A daily rhythmic rhythmic activity activity cycle, cycle,
based on based on 24-hour 24-hour intervalsintervals
Unit 4 Bio Rhthyms 7
The Circadian Rhythm
• We have evolved to fit the 24 hour clock• Even single celled organisms display a 24 hour
cycle • Mammals have evolved to fit the cycle
– Nocturnal v Diurnal
• There are around 100 types of Circadian Cycles (Green 1994)
• Most commonly known is sleep wake cycle – Although this is different in infancy
Unit 4 Bio Rhthyms 8
Development of Circadian Rhythms in Infancy
At what point would you say the
infant’s rhythm becomes
established?
ACTIVITY
• Describe your average day:
• What time do you wake? How do you feel?
• When do you get hungry? When do you have lunch?
• When do you start to feel tired? When do you go to sleep?
Unit 4 Bio Rhthyms 9
Unit 4 Bio Rhthyms 10
Unit 4 Bio Rhthyms 11
morning or night person?
The Night Owl • Shows “morning
syndrome” i.e. awakens as day goes on …
• Goes to bed late – midnight or later
• Wakes late as possible in morning
• Feels ‘ill’ if has to get up at 6am
• Feels tired during the day due to too little sleep
The Morning Lark
• Doesn’t show morning syndrome
• Tends to wake early before 7am
• Active soon after waking
• Struggles to stay up late
• Can fall asleep fast if goes to bed early e.g. 9pm
Unit 4 Bio Rhthyms 12
Other Circadian Rhythms • Temperature regulation
• Cognitive functioning
• Pain tolerance • Certain illnesses are worse at different
times
• e.g. hay fever in the morning, or late at night
• Chronotherapeutics address this
Unit 4 Bio Rhthyms 13
Key Study: Siffre
• Spent some time in a cave
• Absence of all time givers
• Extended his circadian cycle to approx 27 hours
• Spent 179 days in cave (but he thought 151!)
• However, Lavie (2001) puts the shift at only a few minutes using careful controls
What day is it?
Unit 4 Bio Rhthyms 14
The Circadian Shift
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But what gives us our sense of time?
Exogenous Zeitgeber• Outside the body • External cues
– (e.g. your alarm clock)
• Environmental stimuli – (e.g. daylight,
temperature change)
Endogenous Pacemaker • Within the body • Specific bio-chemical
changes – (e.g. melatonin, SCN,
pineal gland)
Unit 4 Bio Rhthyms 16
Suprachiasmic Nucleus (SCN)
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The Suprachiasmic Nucleus
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Endogenous Pacemakers
• small cluster of cells in our hypothalamus called the: Suprachiasmatic nucleus (SCN).
• linked to our visual system
• influenced by the amount of light we detect.
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Endogenous Pacemakers
• SCN can in turn cause the
• pineal gland to produce a hormone called
• melatonin • This can make
you feel sleepy.
Unit 4 Bio Rhthyms 20
24 Hours of Melatonin SecretionOk, what
conclusions would you draw from this chart. Can you explain
why this happens?
Unit 4 Bio Rhthyms 21
The general scientific test for endogenous rhythms
1. Place the organism into an environment devoid of all external patterns
2. (e.g. constant light and temperature) 3. Observe if the rhythmic pattern continues. 4. This would be in a laboratory situation where a
constant environment is maintained. 5. Endogenous rhythms are usually coded in the
organisms DNA, and hence the endogenous pattern is usually inheritable.
Unit 4 Bio Rhthyms 22
DeCoursey et al (2000)
• destroyed the SCN in some chipmunks.
• found that these chipmunks were much more active at night
• however they were also more likely to be taken by nocturnal predators
• Support for the ecological theory in sleep (more on that later)
I may look cute, but just because researchers were a bit cruel to me, you can’t use that as an evaluation!
Unit 4 Bio Rhthyms 23
Internet Resources
http://www.a-levelpsychology.co.uk/online/a2/chapter04/intex1.asp
an interactive resource on sleep-wake cycle
Unit 4 Bio Rhthyms 24
• Watching TV late at night?
• Staying indoors during the winter?
• Solar eclipse?
What about the following:
•Summer in Norway?
•Flying from San Francisco to London?
Unit 4 Bio Rhthyms 25
Disruption of Circadian Rhythms
• Jet Lag (Spitzer et.al.) • Body is out of phase • You think/feel it’s a
different time. • Worse travelling from
the west to an eastern time zone – (e.g. Los Angeles to
London)
Unit 4 Bio Rhthyms 26
Prevention of Jet Lag
Using artificial doses of melatonin can reduce the effect of jet lag
Unit 4 Bio Rhthyms 27
Internet resources
• http://www.a-levelpsychology.co.uk/online/a2/chapter04/intex2.asp
• An interactive resource on jet lag
Unit 4 Bio Rhthyms 28
Common Effects of Shift Work
• Lack of communication between staff
• Lack of ‘teamwork’ • Poorer concentration
on duty tasks • Unsafe conditions • Stress • Shift lag
Unit 4 Bio Rhthyms 29
Shift Lag
• Mental symptoms: – Increased irritability
– Overly emotional
– Forgetfulness
• Physical Symptoms: – Fatigue
– Loss of energy
– Tiredness
Unit 4 Bio Rhthyms 30
Key Studies: Monk & Folkard (1985)
• Interviewed workers who regularly changed shift
• Found changing shifts was better for for:
• Subjective wellbeing • Productivity
Unit 4 Bio Rhthyms 31
Key Studies: Czeisler (1982)
• Workers at a chemical plant in Utah took 16 days to adjust
• Conclusion; workers should move forward in time (clockwise)
• Job satisfaction increased • Productivity rose • Accident rates declined • Workers report more
satisfaction in leisure time
Unit 4 Bio Rhthyms 32
Infradian Rhythms
• for more than one day– e.g. the 28 day
menstrual cycle,
• Tied in closely to the lunar month (the only external cue).
• Evolutionary adaptation?
• nocturnal predation
Unit 4 Bio Rhthyms 33
Menstruation
• Levels in female sex hormones change
• Ovulation • Pre-menstrual
syndrome – (changes in female sex
hormones)
• Menstrual synchrony– (pheromone cues)
Unit 4 Bio Rhthyms 34
Key study: Rienberg (1967)
• Studied girl in cave for 3 months
• Menstrual cycle shortened to 25.7 days
• Took a year to get back to her normal cycle of 27 days
• (By the way, her day lengthened to 24.6 hours – support for Siffre)
Unit 4 Bio Rhthyms 35
Unit 4 Bio Rhthyms 36
The Ovulation Cycle
Ultradian rhythmsThese are rhythms that are
shorter than a day. Such rhythms occur during sleep, but other
ultradian rhythms include excretion from the kidneys and heart rate. People addicted to
nicotine will show an ultradian rhythm — smoking!
Unit 4 Bio Rhthyms 37
Ultradian rhythms in sleepElectroencephalogram (EEG) recordings have revealed that the brain is still active
during sleep, but different states of awareness have distinct patterns of electrical activity
associated with them in the normal individual. Wakefulness, the immediate pre-sleep stage,
light sleep, deep sleep and periods of dreaming (REM sleep) can all be identified
through EEG recording – all ultradian rhythms!
Unit 4 Bio Rhthyms 38
Unit 4 Bio Rhthyms 39
Circannual Rhythms
• Male hamsters testosterone levels change over the year
• Breeding season triggered by longer days
• Lesions in the SCN disrupt this
• Testosterone is secreted all year!
• (Rusak & Zuker 1975)
Unit 4 Bio Rhthyms 40
Fertility and Summer
• Reinberg (1967) study in 600 german schoolgirls
• They tend to start their menstruation during winter months
• Stable menstrual cycles occur more in summer, hence more conceptions
Unit 4 Bio Rhthyms 41
Seasonal Affective Disorder (S.A.D.)
• Lack of daylight
• Increases melatonin
• Fatigue
• Disordered sleep patterns
• Risk of depression
• Treated with UV light and/or melatonin therapy. – For more info follow the
link: http://hcd2.bupa.co.uk/fact_sheets/html/sad.html