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Biorhythms (Circadian rhythms (Research into circadian rhythms (Individual…
Biorhythms
Circadian rhythms
= a pattern of b/h that occurs or recurs approx e/ 24hrs and is set by envir. light levels
Sleep-wake cycle
Believed to be bc of adaptation
Darkness hide the things that may harm us
We are
dinural
Animals are
nocturnal
They use darkness to protect themselves
We are awake in the daylight and sleep at night
Body clocks
Drive our circadian rhythms
Found in each cell
Synchronised by SCN
Homeostasis
When awake we use more energy
As we deplete energy, homoestasis makes us sleepy
We have 2 sleep dips
2-4am
1-3pm
If we are sleep deprived
These are more pronounced
This is why we sleep at night
Low light
Low energy
Other circadian rhythms
Core body temp
Lowest
4:30 AM
36C
Highest
6pm
38C
Hormone production
Melatonin
Helps to induce sleep
SCN sends signals to the
pineal gland
which releases this hormone
Affected by darkness and temp
Research into circadian rhythms
Hughes (1977)
Antarctic station
Hormone production is affected by light levels
Other studies have not found a difference
Studies isolated ptps from daylight and time
But not artificial light
Czeisler et al (1999)
Altered circadian rhythms
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Individual differences
Duffy et al (2001)
Morning ppl
6 am - 10 pm
Evening ppl
10 am - 1 am
Czeisler et al (1999)
Cycle length
Circadian rhythms can vary
13 - 65 hrs
Practical applications
Chemotherapeutic
= study of how timing affects drug treatments
Drug delivery for a particular time of day
E.g. heart attack medication early morning
Evans and Marain (1996)
Novel drug delivery system
Medication can be administered before person goes to sleep
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Temperature is more important than light?
Buhr et al (2010)
Light picked up by SCN
SCN changes body temp
Fluctuations in temp set the timings of cells in the body
Causing tissues and organs to become active and inactive
Endogenous pacemakers
Mechanisms within the body
Govern internal biological rhythms
Inherited, genetic, adaptive
Two main pacemakers
Suprachiasmatic nucleus (SCN)
In the hypothalamus
aka 'master clock'
Controls sleep and arousal
Peripheral body clocks in the organs relating to homeostasis
Can keep time
But need SCN to sycn them
Keeps in sync w/ envir. by sampling light levels
Picked up by the
amacrin cells
in the retina
Pineal gland
Receives info from SCN
To increase or decrease level of
melatonin
Inducing sleep or wakefulness
Each cell has a biological clock
The pacemakers help to keep them in sync
Exogenous zeitgebers
= environmental cues that regulate the biological clock
E.g.
Light
This is the key exogenous factor that affects the sleep/wake cycle
Light levels drop —>
Optic nerve activity decreases —>
SCN activates pineal gland —>
Melatonin is released —>
Brain activity decreases —>
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Temperature
Meals
Social cues
E.g. bedtime
Exercise
Entrianment
= alignment of the internal biological clock to external cues
In the absence of envir cues
SCN operates independently in a 25 hr or longer cycle
Sleep/wake cycle becomes longer than 24hrs
Folkard (1996)
A student volunteered to spend 25 days in a lab
With no access to light or other zeitgebers
At the end of 25 days
Core temp rhythm
24 hours
Sleep-wake cycle
Extended to 30 hours
W/ sleeping periods of 16 hours
W/o zeitgebers of light and activity
Pacemakers in the body got out of sync
Because the SCN had no reference point to co-ordinate them
Ways of studying the brain
Electroencephalogram (EEG)
Large no of small recording electrodes
24 or 32
Placed on scalp
Measures how electrical activity in the brain varies
Over time
In different states
EEGs are most commonly used to study brain waves during the different stages of sleep
Advantages
High temporal resolution
I.e. output is in 'real time'
Non-invasive
Disadvantages
Poor spatial resolution
Can only detect activity in superficial regions of the brain
Event related potentials (ERPs)
Uses EEG equipment
Measures response of the person to a stimuls
Can compare to normal base levels
Repeat this process to create averaging
Measures the base level of activity in the brain
Used to study cognitive processing in response to specific stimuli / inputs
Advantages
Same as EEG
As it uses the same equipment
Can measure 'covert' cognitive processing in response to a stimulus
In the absence of an 'overt' b/hal response
Disadvantage
Requires a large no of trials
To provide meaningful data
Functional Magnetic Resonance Imaging (fMRI)
Used to study which brain regions are active during a task
Active neurons use energy
Glucose and oxygen delivered by haemoglobin
Oxygenated and deoxygenated haemoglobin have different magnetic properties
MRI scanner detects where the haemoglobin is happening
Which areas of the brain are active
Called the BOLD contrast
Blood Oxygenated Level Dependent
Seeing difference between oxy and deoxy-genated blood
Advantages
High spatial resolution
Non-invasive
Does not require exposure to harmful radiation
Disadvantages
Neural activity is not measured directly
Inferred via the increase in blood flow
Low temporal resolution (time)
Expensive
Ptps must stay completely still
Can limit tasks given
Post-mortem
Used to study structural and chemical abnormalities in the brain
In those who have displayed atypical b/h
E.g. Einstein
Charles Whitman
Advantages
Allows detailed study of neurochemical and anatomical aspects of the brain
Allows study of deeper regions in the brain
Disadvantages
Confounding variables
E.g. time since death, drug treatment
When comparing w/ control brains
Method is retrospective
Researcher is unable to follow up on their findings of abnormalities
e.g. Check cognitive function
Ultradian rhythms
=cycles that last less than 24 hours
Repeat more than once a day
e.g. the cycle of sleep stages that occur through the night
Sleep stages
Stage 1
5-15 min
V light sleep
Mixture of alpha and theta waves
Stage 2
5-15 min
Light sleep
Theta waves w/ sleep spindles and K-complexes
Stages 3&4
5-15 min each
Delta waves
Deep sleep
Stage 5
10 min in first cycle
Lengthens in future cycles
After 90 mins
REM sleep
Dreaming occurs
Many beta waves
Evidence for stages comes from EEGs
Alternate between Non-REM and REM sleep
Basic rest-activity cycle
Kleitman (1969)
90 min cycle through sleep stages
Is mirrored during the day
Alertness to fatigue / 90 mins
Planning work around this aids concentration
Individual differences in sleep stages
Differences in the sleep patterns of individuals are usually attributed to differences in non-biological factors
E.g. room temperature, sleep hygiene
However,
Tucker et al (2007)
Ptps studied over 11 consecutive days and nights
In strictly controlled lab envir
So arguably there should be no effect of sleep hygiene, room temp etc
Assessed: sleep duration, time to fall asleep, amount of time in each sleep stage
Found large differences in each of these characteristics
Showed up consistently across the 8 nights
For deep sleep (stages 3 & 4)
Individual differences were particularly significant
Meant difference between ptps not driven by circumstance
Were at least partially biologically determined
Infradian rhythms
=rhythms that have a duration of over 24 hours
Perhaps weekly, monthly or annually
E.g. menstrual cycle
Annual rhythms
In animals
Migration
Hibernation
In humans
Mood
Seasonal affective disorder (SAD)
Aka 'winter depression'
Symptoms more apparent and tend to be severe during the winter
Symptoms often begin in autumn
As days start getting shorter
Often improves and disappears in spring and summer
Although may return each autumn and winter in a repetitive pattern
Effective treatment for SAD is phototherapy
Lightbox stimulating daylight
Eastman et al (1998)
This relived symptoms in up to 60% of sufferers
Found placebo effect
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"Sad is a
circannual rhythm
(it is subject to a yearly cycle). But the symptoms of SAD may be linked to disruptions in certain
circadian rhythms
, including hormone release and the sleep-wake cycle"
Melatonin
Light affects SCN
SCN alters melatonin production
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Wehr et al
SAD patients had longer nocturnal secretion in winter than summer
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Day length
Longer days = lower SAD
Shorter days = higher SAD
Research has shown an influence of latitude on ppl w/ SAD
Michalak and Lam
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Phase shift
Circadian rhythms of SAD patients do not sync w/ the external light conditions
There is a delay
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Heart attacks
Winter
Death
January