biopsychology Flashcards
nervous system
the CNS and PNS
CNS
the brain and spinal cord
origin of all complex commands and decisions
BRAIN is the centre of all conscious awareness
- cerebral cortex: outer layer, highly developed, what distinguishes our higher mental functions from other animals
- 2 hemispheres
SPINAL CORD is an extension of the brain
- responsible for reflex actions
- passes messages to and from your brain
- connects nerves to PNS
PNS
- sends information to CNS from the environment
- transmits messages from CNS to muscles and glands in body
- transmits messages via millions of neurons to and from CNS
sub divided into:
ANS- autonomic nervous system- governs vital functions in the body e.g. breathing, heart rate, arousal, stress
- transmits messages to and from internal body organs
- automatic+ involuntary
- divides into sympathetic and parasympathetic
SNS- somatic nervous system- controls muscle movement, receives information from sensory receptors
- transmits information from receptor cells in the sense organs to CNS
- receives information from CNS that directs muscles to act
ANS
autonomic nervous system- governs vital functions in the body e.g. breathing, heart rate, arousal, stress
- transmits messages to and from internal body organs
- automatic+ involuntary
- divides into sympathetic and parasympathetic
SNS
somatic nervous system- controls muscle movement, receives information from sensory receptors
- transmits information from receptor cells in the sense organs to CNS
- receives information from CNS that directs muscles to act
endocrine system
one of the bodys major information systems that instructs glands to release hormones directly into the bloodstream, towards target organs
gland
an organ in the body that synthesises hormones
hormones
chemical substances/messengers that circulate in the bloodstream and only effect target organs
produced in large quantities
disappear quickly
powerful effects
fight or flight response
the way an animal responds when stressed
- the body becomes psychologically aroused in readiness to fight an aggressor or flee
adrenaline
- a hormone produced by the adrenal glands which is part of the body’s immediate stress response system
- adrenaline has a strong effect on the cells of the cardiovascular system
–> stimulates heart rate, contracting blood vessels, dilating air passages
role of glands and hormones in the endocrine system + relationship to nervous system
- the endocrine system works alongside the nervous system to control vital functions in the body
- the endocrine system acts more slowly than the nervous system but has more widespread, powerful effects
- various glands in the body produce hormones
–> hormones are secreted into the bloodstream and affect any cell in the body that has a receptor for that particular hormone
–> most hormones affect cells in several organs of the body
main glands of endocrine system
pituitary
thyroid
parathyroid
adrenals
pancreas
ovaries
testes
role of thyroid gland
- produces hormone thyroxine
- increases heart rate
- affects cells throughout body, increasing metabolic rates
- affects growth rates
the main endocrine gland
- pituitary gland
‘master gland’ - controls the release of hormones from all other endocrine glands
endocrine and ANS working together: fight of flight
- adrenaline
- often the endocrine and ANS work in parallel during a stressful event
- when a stressor = percieved
1. ANS changes from normal resting state (parasympathetic state) to physiologically aroused (sympathetic state)
- pituitary gland releases adrenocorticotrophic hormone ACTH
- ACTH has an effect on cells in adrenal glands causing them to release adrenaline into the bloodstream
adrenaline triggers psychological changes in the body necessary for fight or flight
- increases heart rate
- increases breathing rate
- dilates pupils
- inhibits digestion
- inhibits saliva production
- contracts rectum
- explain the ‘sick’ feeling
once threat has passed, returned to parasympathetic state
–> actions = antagonistic of sympathetic nervous system
parasympathetic system acts as ‘break’ and reduces activities that were increased in sympathetic
‘rest and digest’
sympathetic vs parasympathetic
sympathetic
- increases heart rate
- increases breathing rate
- dilates pupils
- inhibits digestion
- inhibits saliva production
- contracts rectum
parasympathetic
- decreases heart rate
- decreases breathing rate
- constricts pupils
- stimulates digestion
- stimulates saliva production
- relaxes rectum
using an example, explain what is meant by the fight or flight response
- the fight or flight response is a sequence of activity in the body which occurs when faced with danger or stress
- the body prepares itself for defence or running away
this involves activity of the nervous system and the endocrine system and the secretion of hormones - if you hear a noise that makes you jump, adrenaline will be released from your adrenal glands to increase heart rate
- your body immediately diverts blood away from your stomach to your muscles in order for you to confront a potential attacker or run away
evaluation of fight or flight
+ GRAY
strengths
- acute and chronic stress
our bodies are good at handling short bursts of stressful periods (acute)
- it takes a short time for ANS to return to parasympathetic state
weaknesses
- while the fof response may have been useful for our ancestors, who faced genuinely life-threatening situations
–> modern day life rarely requires such an intense biological response
- furthermore, the stressors of modern day life can repeatedly active our fof response, which can negatively affect our health
e.g. continually increase blood pressure –> damage blood vessels + heart disease
–> suggests that the fof response is a maladaptive response in modern day life - original fof research was conducted using males- researcher bias
- was found later that women will often engage in initial ‘freeze’ response
–> animals are hypervigilent, while they appraise the situation
GRAY- this is to avoid confrontation altogether
this suggests that original research into the fof response is not generalisable but has now been updated to incorporate a variety of human behaviour
neuron
- the basic building blocks of the nervous system
- nerve cells that process and transmit messages through electrical and chemical signals
sensory neurons
carry messages from PNS to CNS.
have long dendrites and short axons
motor neurons
connect the CNS to effectors e.g. muscles and glands
have short dendrites and long axons
relay neurons
connect sensory neurons to motor neurons/ other relay neurons
have short dendrites and long axons
synaptic transmission
the process by which neighbouring neurons communicate with each other by sending chemical messages across the synapse
neurotransmitter
brain chemicals released from synaptic vesicles that relay signals across the synapse from one neurone to another
can be broadly divided into:
- excitatory function
- inhibitory function
once the neurotransmitter crosses the synapse, it is taken up by a poststynaptic receptor site
- i.e. dendrites of next axon
–> chemical message is converted back to electrical impulse + transmission begins again in next neuron
- each neurotransmitter has its own specific molecular structure that fits perfectly into a post-synaptic receptor site- lock + key
- neurotransmitters have specialist functions e.g. causing muscle contraction
excitation
when a neurotransmitter e.g adrenaline. increases the positive charge of the post synaptic neuron
- this increases the likelihood that the neuron will fire and pass on the electrical impulse
inhibition
when a neurotransmitter e.g. seretonin increases the negative charge of the postsynaptic neuron
- this decreases the likelihood that the neuron will fire and pass on the electrical impulse
structure of a neuron
- vary in size from mm<x<m
share same basic structure
CELL BODY (SOMA) INCLUDES
- nucleus
contains the genetic material of cell
- dendrites
branch like structures that carry nerve impulses from neighbouring neurons towards the body
- axon
carries impulses away from cell body down the length of the neuron
- myelin sheath
covers axon
protects axon and speeds up electrical transmission
–> segmented by gaps- nodes of ranvier
speed up transmission by forcing impulse to ‘jump’ across gap
- terminal buttons
communicate with the next neuron in the chain across synapse
role of neurons
100bn in human nervous system
80% of which in brain
by transmitting signals electrically and chemically, provide the nervous system with its primary means of communication
location of neurons
- cell bodies of motor neurons may be in CNS
–> long axons are part of PNS - sensory neurons = outside the CNS, in the PNS as clusters- GANGLIA
- relay neurons- make up 97% neurons- mostly found in brain and visual systems
electric transmission- firing a neuron
- when a neuron is in a resting state, the inside of a cell is negatively charged compared to outside
- when a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a split second, causing an ACTION POTENTIAL to occur
- this creates an electrical impulse that travels down the axon towards the end of the neuron
chemical transmission- synapses
- neurons communicate with each other within groups- NEURAL NETWORKS
- each neuron is separated by the next by a tiny gap - SYNAPSE
- signals WITHIN neurons are transmitted electrically
- signals BETWEEN neurons are transmitted chemically across the synapse
- when the electrical impulse reaches the end of the neuron
–> PRESYNAPTIC TERMINAL
it triggers the release of NEUROTRANSMITTERS from SYNAPTIC VESSELS
summation
- whether a postsynaptic neuron fires is decided by summation
–> the excitatory and inhibitory effects are summed
if the net effect of the postsynaptic neuron is inhibitory, the postsynaptic neuron is less likely to fire
if the net effect is excitatory, more likely to fire
once the electrical impulse is created, it travels down the neuron
therefore, the action potential of the postsynaptic neuron is only triggered if the sum of the excitatory and inibitory signals at one time reaches the threshold
localisation of function in the brain
the theory that different areas of the brain are responsible for specific behaviours, processes, or activities
motor area
a region of the frontal lobe regulating movement
stomasensory area
an area in the parietal lobe that processes sensory information e.g. touch
visual area
a part of the occipital lobe that recieves and processes visual information
auditory area
located in the temporal lobe and concerned with the analysis of speech-based information
broca’s area
an area of the frontal lobe in the LH responsible for speech production
wernicke’s area
an area of the temporal lobe (encircling auditory cortex) in the LH responsible for language comprehension
localisation vs hollism
- during 19c, scientists e.g. Broca and Wernicke discovered that specific areas of the brain are associated with particular physical and psychological functions
before these investigations, scientists generally supported the hollistic theory of the brain- that all parts of the brain were involved in the processing of thoughts and action
- in contrast, B and W argued for localisation of function
–> CORTICAL SPECIALISATION
this is the idea that different parts of the brain perform different tasks and are involved with different parts of the body
–> it follows then, that if a certain area of the brain becomes damaged through illness or injury, the function of that area will also be affected,
action potential
- impulses sent along the axons
an action potential is a rapid rise and subsequent fall in voltage/ membrane potential across a cellular membrane with a characteristic pattern
sufficient current is required to initiate a voltage response in a cell membrane
when an impulse is sent from the cell body, this electrical charge sends the signal down the axon- an action potential
resting state
when membrane potential returns to the resting voltage that occurred before the stimulus occurred
hemispheres of the brain
the main part of the brain (cerebrum) is divided into two symmetrical halves- LH RH
activity on one side of our body is controlled with the opposite hemisphere
LH: speech + language
RH: visual tasks
–> lateralisation
lobes of the brain
the cerebral cortex = divided into 4 lobes
- frontal
- parietal
- occipital
- temporal
–> a lobe is part of an organ that is in some way separate from the rest
- each lobe of the brain is associated with different functions
frontal lobe
at the back of the frontal lobe (in both hemispheres) is the motor area, which controls voluntary movement in the opposite side of the body
–> damage to this area may result in a loss of control over fine movements
parietal lobes
at the front of both parietal lobes = STOMASENSORY area
– separated from motor area by CENTRAL SULCUS
the stomasensory area is where sensory information from the skin e.g. related to touch, heat, pressure, is represented
the amount of stomasensory area devoted to a particular body part denotes its sensitivity
occipital lobe
- at the back of the brain
- visual cortex
- each eye sends information from the RVF to the LVC and vice versa
–> so damage to the LH can produce blindness in part of the RVF of both eyes
temporal lobes
- auditory area
–> analyses speech- based information - damage may produce partial hearing loss
+ damage to wernicke’s area (in temporal lobe) may affect ability to COMPREHEND language
language centres of the brain
broca’s area
- unlike the frontal/parietal/occipital/temporal,
language = restricted to LH - in 1861, Broca identified an area (through post mortem) in the left frontal lobe responsible for speech production
- damage to Broca’s area causes Broca’s aphasia
–> characterised by speech that is slow, laborious, lacks fluency
–> also have difficulty with prepositions anad conjuntions
DOES NOT affect intelligence or other ways of communicating- only speech - broca’s most famous patient was Tan (only word he could say)
language centres of the brain
wernicke’s area
around same time as Broca, Wernicke was describing people who had no problem producing language but severe difficulties understanding it
–> such that their speech was fluent but meaningless
- wernicke discovered a region in the left temporal lobe as being responsible for language understanding
- damage to wernicke’s area causes wernicke’s aphasia
–> often produce nonsense words (neologisms)
evaulation of localisation of function
- EVIDENCE FROM NEUROSURGERY
- EVIDENCE FROM BRAIN SCANS
- COUNTERPOINT
- QUESTIONING LANGUAGE LOCALISATION
- REAL LIFE APPLICATION
- POST MORTEM
strengths
EVIDENCE FROM NEUROSURGERY
- one strength of localisation theory is that damage to areas of the brain has been linked to mental disorders
- CINGULOTOMY- isolating a region, the CINGULATE GYRUS, which has been implicated with OCD
DOUGHERTY ET AL
reported on 44 people with OCD who had undergone a cingulotomy
- at post surgical follow up after 32 weeks
–> 30% met criteria for successful response to surgery
–> 14% partial response
the success of these procedures suggests that behaviours associated with serious mental disorders may be localised
EVIDENCE FROM BRAIN SCANS
TULVING ET AL
- injected radioactive isotope into 6 participants
- to identify different memory stores
–> semantic and episodic memory = stored in diff parts of prefrontal cortex
PETERSEN ET AL
- used brain scans to demonstrate how Wernicke’s area was active during listening tasks and Broca’s area was active during a reading task
–> confirm localised areas for everyday behaviours
- therefore objective methods for measuring brain activity have provided scientific evidence that many brain functions are localised
—> not just based on post mortems
COUNTERPOINT
KARL LASHLEY
- removed areas of the cortex (10-50%) in rats that were learning the route through a maze
- no area was proven to me more useful than any other in terms of their ability to learn the route
- the process of learning seemed to require every part of the cortex
–> suggests that higher cognitive processes e.g. learning, are not localised but distributed in a more holistic way in brain.
QUESTIONING LANGUAGE LOCALISATION
DICK AND TREMBLAY
- 2% modern researchers think that language in the brain = completely controlled by Broca’s/Wernicke’s areas
- advances in brain imaging techniques e.g. fMRI, mean that neural processes can be clearly studied
- language seems to be distributed more hollistically
‘language streams,’ across the cortex inc RH
–> suggests that, rather than being confined to key areas, language may be organised more hollistically
REAL LIFE APPLICATION
- can target therapy to specific areas
–> positive effect on patients
–> good real life application
POST MORTEMS
- brain deteriorates
- EV possible
- cannot see cause + effect
Phineas Gage + evaluation
- Whilst working on a railroad in 1848, 25-year-old Phineas Gage was preparing to blast a section of rock with explosives to create a new railway line
- During the process, a premature explosion drove a tamping iron, 1.1m long, 6mm in diameter, weighing 6 kg, through his left cheek and out of his skull, with such force that it threw him on his back several metres behind.
- Despite his injuries, he remained conscious
- The event rendered him blind in his left eye, and left facial weakness- but no neurological deficits, such as paralysis or tremors.
- However, what was remarkable was the change in Gage’s personality
- Although his memory and cognition had not been altered, his once gentle personality degraded.
- He became rude, disrespectful, angry and unable to accept advice
- This change stemmed from the damage caused to his frontal lobe, which is now considered to be the part of the brain associated with behavioural and emotional responses.
Evaluation
Strengths
- This is a real life example of localisation of the brain.
One part (frontal lobe) was severely damaged, and a change was seen in Gage’s behaviour.
Therefore the frontal lobe can be considered partly responsible for behaviour and emotion
- Predictions can now be made about people’s behaviour when they have experienced injuries to specific areas of the brain
this can help in treating patients, in targeting therapy to specific areas of the brain, and helping patients adjust to new lifestyles.
Therefore this study provides useful real-life application
Weaknesses
- Information about the change in Gage’s personality was taken from details written more than a century ago, so its accuracy is questionable
- As this was a case study, it is difficult to generalise the findings to a wider population so predictions about possible changes in behaviour may not be applicable to everyone.
- As Gage’s accident was so severe, it isn’t possible to determine whether his change in personality was solely due to damage to his frontal lobe- other areas of his brain may have been affected.
an object is presented in the LVF and the split brain patient is asked to pick it up with their rh
- cannot do it without moving head
–> crossing visual field - LVF= interpreted by RH
- have to pick up w rh
- rh = controlled by LH
connection between RH + LH lost so cannot communicate
an object is placed in the lh and split brain patient asked to name it
cannot name
lh –> processed by RH
LH= responsible for speech
connection lost
a word is presented to the RVF and split brain patient asked to name it
can name + select smth similar
RVF –> LH
LH = language centre
an object is placed in RH and split brain patient is asked to find object with same hand
can find object
- not crossing vf
- diff hemisphere
rh = LH
using rh uses LH so stays in LH
object placed in lh and split brain patient is asked to find object with rh
cannot locate
- crosses vf
- diff hemisphere
rh = LH
lh = RH
LH required
no communication between
lh- key
rh- ring
objects hidden within other objects
split brain patient asked to say/find in each hand
could not say ‘key’ but could find it
could say ‘ring’ but couldnt find it
- visual tasks : RH
so can’t say but can find - language: LH
so can say ring
a split brain patient was shown an object in LVF and asked to draw with rh
not able to draw w rh
LVF- RH
RH controls lh so easier w/ lh
a split brain patient shown an object to RVF and asked to draw with lh
able to do it!!!
- all rh participants
- however, all could draw better w lh as being processed by LH
RVF- LH processed
lh draw easier as processed by LH
–> info along optic nerve
two different words are shown to the left (ball) and right (pen) visual field
split brain patients are asked to name one and pick the other up
- processed indepedently
-> find ball, not name
-> name pen not find
RVF- LH
lH = responsible for language
split brain patient shown a face with left half being man and right being woman
- could say there is a woman- could not draw
- could draw man- not say there is one
LVF- man RH processed
RVF = woman LH processed
hemispheric lateralisation
the idea that the two hemispheres of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere
e.g. language = localised and lateralised
split brain research
a series of studies involving people with epilepsy who had experienced surgical separation of the 2 hemispheres to reduce severity
lateralisation vs localisation
lateralisation- there are 2 hemispheres
- for some functions, the localised areas appear in both hemispheres e.g. vision in l/r occipital lobe
localisation: some functions = governed by specific areas of the brain
language in the LH and RH
the two main language centres = in LH
- BROCA’S: left frontal lobe
- WERNICKE’S : left temporal lobe
so language = lateralised + localised
the RH can only produce rudimentary phrases, but contributes to emotion of what’s being said
LH= analyser
RH = synthesiser
motor functions + lateralisation
the brain is cross-wired (contralateral wiring)
visual functions + lateralisation
+ auditory
vision is both CONTRALATERAL, IPSILATERAL
- opposite + same sided
LVF of both eyes connected to RH
RVF of both eyes connected to LH
- enables visual areas to compare the slightly different perspective from each eye- aids depth perception
similar arrangement for auditory input to the auditory area
- the disparity from the 2 outputs helps us locate the source of sounds
SPERRY’S SPLIT BRAIN RESEARCH
evaluation
devised a system to study how two separate hemispheres deal w e.g. speech and vision
Procedure
- 11 people who had a split-brain operation were studied using a special set up in which an image could be projected into a participants RFV (processed by the LH) and the same/ different image could be projected to the LFV (processed by the RH)
- In the normal brain, the corpus callosum would immediately share the information between both hemispheres, giving a complete picture of the visual world.
- However, presenting the image to one hemisphere of a split-brain participant meant that the info cannot be conveyed from that H to the other.
Findings
- When a picture of an object was shown to a participants RFV (linked to LH), the participant could describe what was seen
- But they could not do this if the object was shown to the LFV (RH) – they said there was ‘nothing there,’
- This is because, in the connected brain, messages from the RH are relayed to the language centres in the LH, but this is not possible in the split brain
- Although participants could not give verbal labels to objects projected into the LFV , they could select a matching object out of sight using their left hand (linked to RH)
- The left hand was able to select an object that was most closely associated with an object presented in the LVF
- If a pinup picture was shown to the LVF there was an emotional reaction e.g. giggle, but the participants usually reported seeing nothing or just a flash of light.
Conclusion
- These observations show how certain functions are lateralised in the brain and support the view that the LH is verbal and the RH is ‘silent’ but emotional.
EVALUATION
- quasi experiment- made use of unusual circumstances
–> BUT cannot control EV so lacks internal validity - standardised procedure
- low ecological validity
–> could normally just turn head to change visual field - small sample zide
–> less generalisable - very specific sample
–> epileptic, severed c.c, right handed
hemispheric lateralisation evaluation
RESEARCH EVIDENCE W CONNECTED BRAIN
– fink et al
NO DOMINANT SIDE
– nielsen et al
LATERALISATION VS PLASTICITY
– rogers et al, holland
GENERALISATION ISSUES
SPLIT BRAIN RESEARCH SUPPORT
*RESEARCH EVIDENCE W CONNECTED BRAIN
FINK ET AL
used PET scans to identify which brain areas were active during a visual processing task
- when attending to global elements of an image, RH dominant
- when looking at finer detail, LH dominant
suggests that, at least for visual processing, hemispheric lateralisation is a feature of the connected brain as well as the split brain
*NO DOMINANT SIDE
- limitation = LH analyser and RH synthesiser may be wrong
–> still may have different functions but likely that people don’t have a dominant side that creates a different personality
NIELSEN ET AL
analysed brain scans from over 1000 people 7-29 and did find that people used certain hemispheres for certain tasks (evidence for lateralisation)
–> however no evidence of dominant side
–> suggests left/right brain notion is wrong
*LATERALISATION VS PLASTICITY
- lateralisation is adaptive as it enables tasks to be performed simultaneously with greater efficiency
ROGERS ET AL
- showed that lateralised chickens could find food whilst watching for predators, whilst ‘normal’ chickens couldnt.
- neural plasticity could be seen as adaptive
–> following damage through illness/trauma, some functions can be taken over by non-specialised areas in the opposite hemisphere
HOLLAND
- the language function can ‘switch sides’
GENERALISATION ISSUES
- limitation of Sperry’s research: causal relationships = hard to establish
- the behaviour of Sperry’s split brain participants was compared to a neurotypical control group
- an issue is that none of the control had epilepsy
- major confounding variable
- any differences that were observed may be the result of the epilepsy rather than the split brain
- this means that some of the unique features of the split brain participants’ cognitive abilities may have been due to epilepsy
HOWEVER, FINK’s research supports SPERRY’S conclusions
*SPLIT BRAIN RESEARCH SUPPORT
LUCK ET AL
- showed that split brain participants can perform better than ‘normal’ for certain tasks
e.g. faster at identifying the odd one out from an array of similar objects than normal controls
– supports SPERRY’S findings that the L and R brain = distinct.
*ETHICS
- the split brain operation was not performed for the purpose of the research
- so Sperry’s participants were not deliberately harmed
- full informed consent also contained
- however, the trauma of the operation might mean that the participants did not fully understand the implications of what they agreed to
–> subjected to testing over many years- may have been stressful
plasticity
the brain’s ability to change and adapt as a result of experience and new learning
this generally involves the growth of new connections
functional recovery
a form of plasticity
following damage through trauma, the brain’s ability to redistribute/ transfer functions usually performed by a damaged are(s) to other undamaged area(s)
brain plasticity + synaptic pruning (infancy–>adulthood)
- during infancy, the brain experiences rapid growth in the number of synaptic connections it has
(around 2x as many as adult) - as we age, rarely used connections are deleted and frequently used connections are are strengthened
—> synaptic pruning
synaptic pruning
- enables lifelong plasticity where new neural connections are formed in response to new demands of the brain
research into plasticity
MAGUIRE
DRAGANSKI ET AL
MAGUIRE ET AL
- London taxi drivers
- found significantly larger volume of grey matter in the posterior hippocampus than in matched control group
–> this part of the brain is associated with the development of spatial and navigation skills in animals
- as part of training, taxi drivers must take a test to assess their recall of streets
- this learning experience alters the structure of their brains
–> longer been in job, more pronounced it was
DRAGANSKI ET AL
- learning induced changes to medical student’s brains 3 months after their final exams compared to 3 months before
- brain imaging detected changes to posterior hippocampus and parietal cortex- as a result from learning
plasticity evaluation
NEGATIVE PLASTICITY
medina et al
+ phantom limb syndrome
AGE AND PLASTICITY
bezzola et al
SEASONAL BRAIN CHANGES
tramontin and brenowiz
*NEGATIVE PLASTICITY
- limitation of plasticity = may have negative behavioural consequences
MEDINA ET AL
- the brains adaption to prolonged drug use leads to poorer cognitive functioning in later life+ increased risk of dementia
phantom limb syndrome
- 60-80% amputees have continued sensation in the missing limb as if it were still there
- usually unpleasant, painful
- thought to be due to cortical reorganisation in the stomasensory cortex that occurs as a result of limb loss
suggests that the brain’s ability to adapt to damage is nor always beneficial
*AGE AND PLASTICITY
- strength- plasticity may be a lifelong ability
- in general, plasticity reduces with age
BEZZOLA ET AL
- demonstrated how 40 hours of golf training produced changes in the neural representations of movement in participants 40-60
- using fmri, researcher observed reduced motor cortex
activity in the golfers compared to a control group
—> suggests more efficient neural representations after training
this shows that neural plasticity can occur throughout life
SEASONAL BRAIN CHANGES
- there may be seasonal plasticity in the brain in response to environmental changes
- e.g. the suprachiasmatic nucleus SCN, which regulates the sleep/wake cycle
TRAMONTIN AND BRENOWITZ
–> evidence it shrinks in all animals during spring and expands throughout autumn
however, much work on seasonal plasticity has been done on animals, human behaviour may be different
functional recovery
- after brain trauma
- what happens to the brain during recovery
axonal sprouting
denervation supersensitivity
recruitment of homologous areas on opposite sides of the brain
after brain trauma
- following a physical injury, or other forms of trauma e.g. stroke, unaffected areas adapt and compensate for those that are damaged
- the functional recovery that may occur in the brain after trauma is an example of neural plasticity
- healthy brain areas may take over the functions of those that are damaged, destroyed or missing
- neurocientists suggest that this occurs quickly after trauma (spontaneous recovery) and then slows down after several weeks/ months
- at this point, the indiviual may require rehabilitative therapy to further their recovery
what happens to the brain during recovery
- the brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage
- secondary neural pathways that would not be typically used to carry out certain functions are activated (unmasked) to enable functioning to continue, often in the same way as before
this process is supported by a number of structural changes in the brain:
- axonal sprouting
the growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways - denervation supersensitivity
occurs when axons that do a similar job become aroused to a higher level to compensate for the ones that are lost
— however, can have the negative effect of oversensitivity to messages e.g. pain - recruitment of homologous areas on opposite sides of the brain
specific tasks can still be performed e.g. brocas area being damaged on the LH may mean function shifts temporarily to the right.
evaluation of functional recovery
REAL WORLD APPLICATION- constraint-induced movement therapy
COGNITIVE RESERVE so EV
SMALL SAMPLES
and
NATURAL EXPERIMENT/OBSERVATIONS
OBJECTIVITY
ETHICS
*REAL WORLD APPLICATION
- strength of functional recovery
- understanding processes involved in plasticity has contributed to neurorehabillitation
- understanding that axonal growth is possible encourages new therapies to be tried
—> e.g. constraint- induced movement therapy
shows that research into functional recovery is useful as it helps medical professionals know where interventions should be made
*COGNITIVE RESERVE
- limitation- levels of education may influence recovery rates
- time spent in education = cognitive reserve- as this increases, their chance of disability free recovery increases
- 40% of those who achieved DFR>16 yrs
- 10%<12 yrs
implies that people with brain damage who have insufficient DFR are less likely to achieve full recovery
SO lots of E.V- effectiveness of plasticity is not determined by the individual but many factors.
*SMALL SAMPLES
- functional recovery research normally uses very small samples and no control group
- this leads to low levels of generalisability
NATURAL OBSERVATION/EXPERIMENT
- limited control of variables
- participants have suffered multiple injuries. usually in trauma
–> many EV to contribute to the recovery process
*OBJECTIVITY
- using fmri = objective
–> allows drug therapies to be developed
*ETHICS
- forcing someone into therapy after a traumatic event
why are brain scanning techniques used in medicine/research
- for medical purposes in diagnosis of illness
- in psychological research, to investigate localisation + functions of diff parts of the brain
fMRI
- how it works
- evaluation
- works by detecting the changes in blood oxygenation and flow that occur as a result of neural activity in specific parts of the brain
- when a brain area is more active, it consumes more oxygen so blood flow is directed to that area
a HAEMODYNAMIC response - detects radio waves from changing magnetic fields
- fMRI produces 3D images (ACTIVATION MAPS) showing which parts of the brain are involved in particular mental processes
- this has important implications for our understanding of localisation of function
*
strengths
- unlike scanning techniques e.g. PET, does not rely on the use of radiation
—> virtually risk-free, non-invasive, straightforward
- produces images with high spatial resolution, depicting detail by the mm
—> provides clear picture of how brain activity is localised
—> fMRI can safely provide a clear picture of brain activity
*
limitations
- fMRI is expensive compared to other neuroimaging techniques
- has poor temporal resolution- around a 5-second time lag behind the image on screen and initial firing of neuron activity
—> means that fMRI may not truly represent moment-to-moment brain activity
Electroencelephalogram EEG
- how it works
- evaluation
- EEG measures electrical activity within the brain via electrodes fixed onto scalp using skull cap
- a scan recording represents brainwave patterns from the action of thousands of neurons, providing an overall account of brain activity
- EEG is often used by clinicians as a diagnostic tool and unusual arrhythmic patterns of activity mat indicate neurological abnormalities e.g. epilepsy, tumors, or some sleep disorders
*
strengths
- has been useful in studying the stages of sleep and in diagnosing conditions e.g. epilepsy, a disorder characterised by random bursts of activity in the brain that can easily be detected on screen
- unlike fMRI, has extremely high temporal resolution
–> can accurately detect activity at the resolution of 1ms
–> shows real world usefullness
*
limitations
- main drawback = generalised nature of information recieved (from many thousands of neurons)
- EEG signal = not useful for pinpointing the exact source of neural activity
—> therefore does not allow researchers to distinguish between activities originating in different but adjacent locations - although EEG has many scientific applications, it is overall a general measure of brain activity
- however, within EEG data are contained all the neural responses associated with specific sensory, cognitive and motor effects
- as such, we can isolate these responses
- using a statistical averaging technique, all extraneous brain activity from original EEG is filtered out, leaving only those responses that relate to a specific stimulus
—> WHAT REMAINS ARE EVENT RELATED POTENTIALS (ERP)
event-related potential ERPs
- how it works
- evaluation
- although EEG has many scientific applications, it is overall a general measure of brain activity
- however, within EEG data are contained all the neural responses associated with specific sensory, cognitive and motor effects
- as such, we can isolate these responses
- using a statistical averaging technique, all extraneous brain activity from original EEG is filtered out, leaving only those responses that relate to a specific stimulus
—> WHAT REMAINS ARE EVENT RELATED POTENTIALS (ERP) - types of brainwave triggered by particular events
- research has revealed many different forms of ERP and how they’re linked to cognitive processes e.g. attention and perception
*
strengths
- limitations of EEG= addressed through use of ERP
i.e. can isolate and pinpoint the specific effect of certain stimuli
- bring much more specificity to the measurement of neural processes than raw EEG data
- as ERPs are derived from EEGs, they have excellent temporal resolution, esp compared to fMRI
–> so are frequently used to measure cognitive functions and deficits e.g. allocation of attentional resources and maintenance of working memory
*
limitations
- lack of standardisation in ERP methodology
–> difficult to confirm findings between studies
- in order to establish pure data, background ‘noise’ and EV must be completely eliminated
–> difficult to achieve
post mortem examination
- how it works
- evaluation
- a technique involving the analysis of a person’s brain following their death
- in psych. research, post mortem brains are likely those with a rare disorder and have experienced unusual deficits in cognitive processes/ behaviour
- areas of damage are examined after death to establish the likely cause
- compare with neurotypical brains to ascertain extent of difference
*
strengths
- pm evidence was essential in providing a foundation for early understanding of key processes in the brain
–> Broca and Wernicke relied on post-mortem studies in establishing links between language, brain and behaviour decades before neuroimaging
- pm was used to study HM’s brain to identify the areas of damage, which could then be associated with his memory deficits
—> post mortems continue to provide useful information
*
limitations
- causation is difficult to establish
–> observed damage may be linked to unrelated trauma/ decay
- pm studies raise ethical issues of consent from the individual before death
–> may not be able to give informed consent
e.g. HM couldnt form new memories so could not give consent
–> challenges usefulness of pm
methods of investigating the brain
- brain scans
- twin, adoption, family studies
- selective breeding
- neurotransmitter… urine/blood test
temporal resolution
activity of scanner in relation to time
i.e. length of the delay between brain activity + scanner
increased delay, decreases resolution
spatial resolution
the smallest feature of the brain that is visible when performing a task
—> differentiates different brain regions
longitudinal study
research taking place over a long period of time, using the same sample
SIFFRE’S CAVE STUDY 1962
+ evaluation
IV: his environment- cave/normal life over duration of study
DV: his natural circadian rhythm— duration of his sleep/wake cycle
EV: natural light- no access, health- constantly monitored, social interaction- alone
experimental method: lab- controlled setting + variables
experimental design: repeated measures
- spent several extended periods underground to study the effects of his own biological rhythms
- deprived of exposure to natural light and sound, but with access to adequate food and drink, Siffre spent 2 months in the caves
no exogenous zeitgebers, only relied on endogenous pacemakers - left mid-september, believing it to be mid-august
- a decade later he repeated the experiment but for 6 months
- in each case, his ‘free running’ biological rhythm settled down to around 25 hours, though he did sleep/wake in a regular cycle
*
strengths
- same sample –> limited ppt variables
- lab experiment –> high control of variables inc EV, high internal validity
- real-world benefits
–> medical treatments- understanding levels of hormones @ any one time allows us to diagnose drugs when they will be most effective
- longitudinal study–> lots of data collected
- standardised procedure –> can repeat
*
weaknesses
- studies like these have a high drop out rate so incomplete research obtained
- Siffre as the researcher and participant –> researcher bias
–> very small samples
- there = individual differences in sleep/wake cycles so cannot generalise
- lab experiment –> low mundane realism, low ecological validity
- lacks generalisability
—> we cannot free- run
however, within 6 months, circadian re-balances itself and is still close to our natural day
- ethics
—> protection from harm
- there is still light
–> artificial lights so not completely natural
not completely influenced by social factors
biological rhythm
distinct patterns of changes in body activity that conform to cyclical time periods.
are influenced by:
- internal body clocks- endogenous pacemakers
- external changes to environment- exogenous zeitgebers
circadian rhythms
biological rhythms subject to 24hr cycle, which regulate a number of body processes e.g. sleep/wake cycle and changes in core body temperature
biological rhythms that occur many times throughout the day
ultradian rhythms
biological rhythms that take longer than a day to complete
infradian rhythms
biological rhythms that take MUCH longer than a day to complete
circannual rhythms
the sleep/ wake cycle
- exogenous involved
- endogenous involved
- daylight is an important exogenous zeitgeber on our sleep/wake cycle
—> it is the reason we feel alert during the day and sleepy at night
however, the sleep/wake cycle is also governed by an endogenous pacemaker- the suprachiasmatic nucleus SCN
- the SCN lies just above the optic chiasm, which provides information to the eye about light
- exogenous zeitgebers (light) can reset the SCN
- melatonin production (makes us feel sleepy) increases in absence of light
core body temperature - circadian rhythm
FOLKARD ET AL
GUPTA
- varies by about 2degress in 24hrs
- lowest (36) around 4am
- highest (38) around 6pm
- evidence suggests that body temperature may have an effect on cognitive performance- the warmer we are internally, the better the performance is
*
FOLKARD ET AL
- children who had stories read to them at 3pm had superior recall and comprehension after a week compared to children who heard the same stories at 9am
GUPTA
- improved performance on IQ tests when participants were assessed at 7pm compared to 9am and 2pm
circadian rhythms evaluation
*SHIFT WORK
- strength of research into circadian rhythms = provides understanding of adverse consequences when they are disrupted
—> DESYNCHRONISATION
e.g. night shift workers experienced a period of reduced concentration around 6am (a CIRCADIAN TROUGH) so accidents are more likely
ASCHOFF AND WEVER
FOLKARD ET AL
–> other sleep/wake cycle studies
ASCHOFF AND WEVER
- a group of participants spent 4 weeks in a WWII bunker, deprived of natural light
- all but one (29) ppt displayed a circadian rhythm 24-25 hrs
—> both siffre’s and this bunker study suggest that the ‘natural’ sleep/wake cycle may be longer than 24hrs
- but it is entrained by exogenous zeitgebers associated with our 24 hour day e.g. daylight hours, mealtimes
despite this, we should not overestimate the power of exogenous zeitgebers on our internal body clock
*
FOLKARD ET AL
- 12 people lived in a dark cave for 3 weeks, going to bed when a clock said 11:45pm and waking when it said 7:15am
- over the course of the study, the researchers gradually speeded up the clock so an apparent 24hr day lasted 22 hrs
- only 1 ppt could comfortably adjust
—> this suggests the existence of a strong free-running circadian rhythm that cannot be easily overridden by exogenous zeitgebers
evaluation of circadian rhythms
SHIFT WORK- REAL LIFE APP
boivin
knutsson
COUNTERPOINT- CORRELATIONS: OTHER FACTORS
solomon
MEDICAL TREATMENT
bonton et al
INDIVIDUAL DIFFERENCES
czeisler, duffy, siffre
SHIFT WORK
- strength of research into circadian rhythms- provides understanding of the adverse consequences when they are disrupted- DESYNCHRONISATION
- e.g. night shift workers experienced a period of reduced concentration around 6 in the morning- CIRCADIAN TROUGH–> accidents/mistakes more likely *BOIVIN
- research has also linked shift work to poor health- shift workers = 3x more likely to develop heart disease than people with typical work patterns *KNUTSSON
—> shows that research into the sleep/wake cycle may have real-world economic implications in terms of how to manage worker productivity
*
COUNTERPOINT
- studies investigating the effects of shift work tend to use correlational methods
- this means it’s difficult to establish whether desynchronisation of the sleep/wake cycle is actually having an effect
— there may be other factors
*SOLOMON
high divorce rates in shift workers may be due to the strain of deprived sleep and other influences, e.g. missing out on important family events
–> suggests that it may not be biological factors that create the adverse consequences affected with shift work.
*
MEDICAL TREATMENT
- strength: circadian rhythm research has been used to improve medical treatments
- circadian rhythms co-ordinate a number of the body’s basic processes e.g. heart rate, digestion, hormone levels
–> rise and fall during 24hrs –> led to chronotherapeutics- how medical treatment can be administered in a way that corresponds to a person’s biological rhythm
e.g. aspirin as a treatment for heart attacks is best taken at night (heart attacks = most likely in morning)
*BONTEN ET AL
–> shows that circadian rhythm research can help increase the effectiveness of drug treatments
*
INDIVIDUAL DIFFERENCES
- limitation of research = generalisation = difficult
ASCHOFF + WEVER AND SIFFRE’S research uses very small samples, even though it seems that people’s skeep/wake cycles vary greatly
- CZEISLER: individual differences 13-65hrs
- DUFFY: some have a natural preferences for going to bed and rising early (larks) or the opposite (owls)
- SIFFRE: his own sleep/wake cycle has slowed as he aged
—> difficult to use research data to discuss anything more than averages
infradian rhythm
type of biological rhythm with a frequency of less than 1 cycle every 24 hrs e.g. menstruation, seasonal effective disorder
ultradian rhythm
a type of biological rhythm with a frequency of more than 1 cycle in 24h
infradian rhythms: the menstrual cycle
- what happens
- governed by monthly changes in hormone levels which regulate ovulation
- the cycle refers to the time between the first day of a period, when womb lining is shed, to the day before the next
- typical cycle = approx. 28 days
- during each cycle, rising levels of oestrogen cause the ovary to develop an egg and release it (ovulation)
- after ovulation, progesterone helps the womb lining grow thicker, ready for pregnancy
- if pregnancy does not occur, the egg is reabsorbed and the womb lining leaves the body
synchronising the menstrual cycle
STEM AND MCCLINTOK
- although the cycle is an endogenous system, evidence suggests that it may be influenced by exogenous factors e.g. cycles of other women
–> demonstrated how menstrual cycles may synchronise due to pheromones
*
- studied 29 women with a history of irregular periods
- samples of pheromones were gathered from 9 of them at different stages of their cycles, via a cotton pad under their armpit
- the pads were worn for at least 8 hours- ensure pheromones picked up
- sterilized, then rubbed on other ppt’s upper lip
- ppt given pad for corresponding day of each sample
–> found that 68% women experienced changes totheri cycle which brought them closer to their ‘odour donor’
—-> QUASI EXPERIMENT LACKS CONTROL
seasonal affective disorder SAD
+ melatonin
- a depressive disorder with a seasonal pattern of onset
- similar to depression, main symptoms = persistent low mood, general lack of activity
- symptoms = triggered during winter when no. daylight hours is reduced
SAD is a type of circadian rhythm- circannual rhythm- yearly cycle
- however, also classed as circadian as the experience of SAD may be due to the disruption of the sleep/wake cycle which can be attributed to prolonged periods of daily darkness during winter
the hormone melatonin may also contribure to SAD
- during the night, the pineal gland secretes melatonin until dawn when there is an increase in light
- during winter, lack of light in the morning means that this process continues for longer
- this is thought to affect the production of seretonin in the brain, a hormone linked to the onset of depressive symptoms
infradian rhythms- evaluation
EVOLUTIONARY BASIS
METHODOLOGICAL LIMITATIONS
–> hard to generalise as confounding variables
REAL WORLD APPLICATION
EVOLUTIONARY BASIS
a strength of menstrual synchrony research = it may be explained by natural selection
- synchronisation of the menstrual cycle maybe was advantageous for our ancestors- it may have been advantageous for women to menstruate together and become pregnant at the same time
- in a social group, this would allow babies who had lost their mothers to have access to breastmilk, improving their survival chances
—> so synchronisation may be an adaptive strategy
METHODOLOGICAL LIMITATIONS
- there are many factors that affect menstrual cycles e.g. change in diet, stress
–> may act as confounding variables
- so any pattern of synchronisation could just be chance
- these studies are therefore difficult to replicate
REAL WORLD APPLICATION
- one of the most effective treatments for SAD is light therapy, a box which stimulates a very strong light to reset the body’s internal clock
–> worked in around 80% people
- also preferred over antidepressants to treat SAD - safer
HOWEVER, light therapy can produce headache and eye strain
- also a relapse rate of 46% over successive winters, compared to 27% in a control group recieving CBT
ultradian rhythms- the sleep cycle
+ stages
- the sleep cycle is a prominent ultradian rhythm
- 5 distinct stages that altogether span 90 minutes- continues throughout the night
–> each stage = characterised by a different level of brainwave activity which can be monitored on an EEG- measuring the change in neural activity during sleep
STAGE 1 and 2
- light sleep, easily woken
– stage 1: brain waves have a high frequency and short amplitude - alpha waves
– stage 2: alpha waves continue, with occassional random changes in pattern- SLEEP SPINDLES
STAGES 3 AND 4
- deep sleep/ slow wave sleep SWS
- brain waves= delta waves with lower frequency and higher amplitude
- difficult to wake
STAGE 5
- REM sleep
- the body is paralysed, yet brain activity resembles an awake one
- brain produces theta waves
- eyes move around
- dreams most often occur in REM, but can occur in deep sleep
ultradian rhythms, evaluation
IMPROVED UNDERSTANDING- PRACTICAL VALUE
INDIVIDUAL DIFFERENCES
THE SLEEP LAB
IMPROVED UNDERSTANDING
- has improved understanding of age-related changes in sleep
- SWS reduces with age
- growth hormone = mostly produced during SWS and is therefore reduced in older people
- the resulting sleep deficit may explain various issues with old age e.g. decreased alertness
- to increase SWS, relaxation and medication = used
—> so knowledge of ultradian rhythms has practical value
INDIVIDUAL DIFFERENCES
- limitation- significant variation between people
- research has shown large differences between the durations of stages 3 and 4- likely to be biologically determined
- so difficult to describe ‘normal sleep’ in a meaningful way
THE SLEEP LAB
- one of the benefits of conducting studies of sleep in lab settings is the control of EV
- this means that researchers can exclude temporary variables e.g. noise or temperature, that may affect sleep
—> objective + reliable
HOWEVER, lab studies involve being attached to complicated machinery, leading to participants sleeping in an environment unlike ordinary sleep, so low internal validity
RANDY GARNER SLEEP DEPRIVATION EXPERIMENT
+ evaluation
In 1964, 17 year old Gardner broke the record for the longest time a human had gone without sleep
- The main aim of this study was to investigate the effect of prolonged sleep deprivation on human cognitive and physiological function.
- He stayed awake for 11 days and 24 minutes
- He was monitored by a team of researchers in a hospital
- As the days progressed, he experienced a range of psychological and physiological effects due to sleep deprivation
- By the end of the experiment he was reported to have significant cognitive impairments, including difficulty with simple tasks, and a decline in motor skills
- After the experiment, he was able to sleep for 14 hours, and reportedly recovered without any lasting negative effects
He experienced:
- Mood changes, notably increased irritability
- Impaired judgement
- Physical symptoms such as headaches, bodily discomfort
- Altered perception- visual and auditory distortions, so difficult to perceive his own environment
- Difficulty with motor skills- coordination and reaction times were impaired
- Disorientation- sometimes felt confused about time and place and experienced hallucinations
Independent variable: amount of sleep deprivation- manipulated by keeping Gardner awake for an extended period of time
dependent variables:
- Cognitive performance- memory, concentration,
decision making
- Emotional state- mood changes, irritability
- Physical health- fatigue, headaches
- Perceptual changes- hallucinations, altered
perception
- Motor skills- coordination, reaction times
Controlled variables
- The environment in which he was monitored
- The tasks he was engaged in during his awake period (tasks that assessed his cognitive function)
*
strengths
- real life study/ scenario
- wide range of data across many different tasks- cognitive, emotional, physical = HOLLISTIC APPROACH
- long duration, measured short and long term effects of sleep deprivation
*
weaknesses
- single subject- limits generalisability, as individual responses vary significantly
- lack of control group- no comparison, so difficult to determine how his experience compares to those who are not sleep deprived
- subjective reporting as some self-report used
endogenous pacemakers
internal body clocks that regulate many of our biological rhythms
e.g. the influence of the suprachiasmatic nucleus on sleep/wake cycke
exogenous zeitgebers
external factors that affect/ entrain our biological rhythms e.g. influence of light on sleep/wake cycle
sleep/wake cycle
a daily cycle of biological activity based on 24hr period that is influenced by regular variations in the environment e.g. alterations of night/day
the suprachiasmatic nucleus
- tiny bundle of nerve cells in hypothalamus of each hemisphere
- one of the primary endogenous pacemakers in mammalian species
- influential in maintaining circadian rhythms e.g. sleep/wake cycle
- nerve fibres connected to the eye cross in the optic chasm on their way to the left and right visual area of the cerebral cortex
- SCN lies just above the optic chasm
- it recieves information about light directly from this structure
- continues even with out eyes closed, enabling the biological clock to adjust to changing patterns of daylight whilst we’re asleep
animal studies and the SCN
DECOURSEY ET AL
RALPH ET AL
DECOURSEY ET AL
- destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days
- the sleep/wake cycle disappeared and by the end of the study, a significant proportion had been killed by predators (awake and active when meant to be sleeping)
*
RALPH ET AL
- bred ‘mutant’ hamsters with a 20hr sleep/wake cycle
- when SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the s/w cycle of the 2nd group defaulted to 20hrs
the pineal gland and melatonin
the SCN passes the information on day length and light that it recieves to the pineal gland, behind the hypothalamus
–> an endogenous mechanism governing sleep’wake cycle
- during the night, the pineal gland increases production of melatonin, a chemical that induces sleep and is inhibited in periods of wakefulness
- melatonin has also been suggested as a causal factor of SAD.
endogenous pacemakers evaluation
BEYOND SCN
DAMIOLA ET AL
INTERACTIONIST SYSTEM
ETHICS
BEYOND THE SCN
- One limitation of SCN research is that it may obscure other body clocks
-There are numerous circadian rhythms in many organs and cells in the body
o Peripheral oscillators
-They are influenced by the actions of the SCN, but also act independently
DAMIOLA ET AL
-Changing the feeding patterns of mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected
—> This suggests other complex influences on the sleep/wake cycle
*
INTERACTIONIST SYSTEM
Another limitation: endogenous pacemakers cannot be studied in isolation
- Total isolation studies e.g. Siffre’s are rare
Siffre used artificial light which could have reset his biological clock
-In everyday life, pacemakers and zeitgebers interact, and it may make little sense to isolate them for research
*
ETHICS
- Animal studies of the sleep/wake cycle are justified because there are very similar mechanisms at work across species
- The existence of SCN and a pineal gland in the brains of e.g. chipmunks mean that generalisations can be made to the human brain, as the mammalian brain has similar structures.
- However, e.g. in DeCoursey’s study, the animals were treated unethically, exposed to risk when returned to their natural habitat and most died.
exogenous zeitgebers and the sleep/wake cycle
LIGHT
CAMPBELL AND MURPHY
SOCIAL CUES
External factors in the environment that reset our biological clocks through entrainment
- In the absence of external cues, the free running biological clock that controls the sleep/wake cycle continues in a distinct cyclic pattern (Siffre’s study)
- This free-running cycle is ‘brought into line’/ entrained by environmental cues
–> So there is an interaction between internal and external factors
*
*
LIGHT
- Light is a key zeitgeber in humans
- It can reset the body’s main endogenous pacemaker, the SCN and so is important in the sleep/wake cycle
- Light also has an indirect influence on key bodily processes that control functions like hormone secretion and blood circulation
CAMPBELL AND MURPHY
Demonstrated that light may be detected by skin receptor sites on the body, even when the same information is not received by the eyes
- Fifteen participants were woken up at various times and a light pad was shone on the back of their knee
- the researches managed to produce a deviation in their usual sleep/wake cycle by up to 3 hours
- this suggests that light is a powerful exogenous zeitgeber that may not need to rely on the eyes to exert its influence on the brain
*
*
SOCIAL CUES
- at about 6 weeks old, the circadian rhythms begin and, by about 16 weeks, babies’ rhythms have been entrained by the schedules imposed by parents, inc mealtimes and bedtimes
- research on jet lag suggests that adapting to local times for eating and sleeping (rather than responding to your own hunger/ fatigue) is effective in entraining circadian rhythms.
exogenous zeitgebers evaluation
Environmental observations
- limitation: exogenous zeitgebers do not have the same effect in all environments
- the experience of people who live in places with very little light/darkness
- e.g. people who live in the arctic circle have similar sleep patterns all year round, despite spending around 6 months in almost total darkness
—-> this suggests that the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light
*
Case study evidence
- evidence challenges the role of exogenous zeitgebers
MILES ET AL
- recount the study of a man, blind from birth, who had an abnormal circadian rhythm of 24.9 hours
- despite exposure to social cues, such as regular mealtimes, his sleep/wake cycle could not be adjusted
- this suggests that social cues alone are not effective in resetting the biological rhythm
**
AGE-RELATED INSOMNIA
- evidence suggests that people have poorer quality sleep as they age
- this may be due to natural changes in the circadian rhythm –> falling asleep earlier
- however, studies have suggested that exogenous factors maybe more responsible
*
HOOD ET AL
found that management of insomnia was improved if elderly people were generally more active and had more exposure to natural light.
