Biopsychology

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  • Created on: 24-10-17 13:09

THE NERVOUS SYSTEM

The nervous system is a specialised network of cells in the human body & is our primary internal communication system. 2 main functions: 1) To collect, process and respond to info in the environment. 2) To co-ordinate the working of different organs and cells in the body.

THE CENTRAL NERVOUS SYSTEM - Made up of the brain and spinal cord ( the origin of all complex commands and desicions). The brain is the centre of all conscious aqareness. The brains outer layer( cerebral cortex) is highyl developed in humans and is what distinguishes our higher mental functions from those of animals.

The spinal cord is an extension of the brain. Responsible for reflex actions. It passes messages to and from the brain and connects nerves to the PNS.

THE PERIPHERAL NERVOUS SYSTEM - Transmits messages via millions of neurons to and from the CNS. Further subdivided into 2: 1) Autonomic nervous system - Governs vital functions in the body e.g. breathing, heart rate, digestion. 2) Somatic nervous system - Controls muscle movement and recievs info from the sensory receptors.

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THE ENDOCRINE SYSTEM

The endocrine system instructs glands to release and produce hormones directly into the bloodstream. The hormone (chemical substance) affects any cell in the body that has a receptor for that particular hormone. Most hormones affect several organs or throughout the entire body, leading to many diverse and powerful responses. e.g. the thyroid gland produces the hormone thyroxine which affects cells in the heart by increasing heart rate and also affects your metabloic rate which affects growth.

The pituitary gland is often called the 'master gland' because it controls the release of hormones of all the othe endocrin glands in the body. The pituitary gland is controlled by the hypothlamus.

When a stressor is pervieved tha ANS changes from its normal resting state (parasympathetic state) to the phsiologically aroused sympathetic state. The stress hormone adrenaline is released from the adrena medulla into the bloodstream. Adrenaline triggers physiological changes in the body (increased heart rate, inhibiting digestion, inhibits saliva production etc.) which creates an arousal necesary for the fight or flight response. All this happens for acute stresors (short- lived stressors). Once the threat has passed, the parasympathetic nervous system returns the body to its resting state.

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THE STURCTURE AND FUNCTIONS OF NEURONS

Neurons - nerve cells that process and transmit messages through electical and chemical signals.

Types of neruons: 1) Motor neurons - Connect the CNS to effectors such as musles and glands. They have short dendrites and long axons. 2) Sensory neurons - Carry messages from the PNS to the CNS. They have long dendrites and short axons. 3) Relay neurons - Connect the sensory neurons to the motor or other relay neurons. Short dendrites and short axons.

The structure of a neuron - Neuron vary in size form less than 1 mm 1m.  

The cell body includes a nuclues which contains the genetic material of the cell. Dendrites carry nerve impulses from neighbouring neurons to the cell body. The axon carries impulses away from the cell body down the length of the neuron. The axon is covered in a fatty layer of myelin sheath that protects the axon and speeds up electrical transmission of the impulse. At the end there is the axon terminal which communicate with the next neuron in the chain acorss a gap known as the synapse.

Electrical transmission - When a neuron is activated by a stimulus, the inside of the cell becomes postively charged for a split second causing an action potential to occur. This creates and electrical impulse that travels down the axon towards the end of the neuron.

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SYNAPTIC TRANSMISSION

Signals within neurons are transmitted electrically but between neurons they are transmitted chemically by synaptic transmission.

1) The nerve impulses travel down an axon of a pre-synaptic neuron.

2)  When the electrical nerve impulse reahes the end of the pre-synaptic neuron it triggers the release of neurotransmitters from tiny sacs called synaptic vesicles.

3)Neurotransmitters then carry the signal across the synaptic gap. They bind to receptor sites on the post-synaptic cell that then become activated. Once the receptors have been activated, they either produce excitatory or inhibitory effects on the post-synaptic cell.

Excitatory neurotransmitters (e.g. noradrenaline) make the post-synaptic cell more likely to fire the message onto the next neuron because it increaes the positive charge of the post synaptic neuron, whereas inhibitory neurotransmitters (e.g. serotonin) make them less likely to fire because it makes the charge more negative.

The neurotransmitters left in the synpase are taken back into the pre synaptic neuron or broken down by enzymes.

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LOCALISATION OF FUNCTION IN THE BRAIN

Scientists such as Broca and Wernicke discovered that specific areas of the brin are associated with particular physical and psychological functions. Before these investigations, scientists generally supported the holistic theory (all parts of the brain were involved in the processing of thought and action). They also argued for localisation of function  which is that different parts of the brain perform different tasks and so if a certain area of the brain becomes damaged, the function  assoicated with that area will also be affected.

Activity on the left- hand side of the body is controlled by the right hemisphere and activity on the right hand side by the left hemisphere. The outer layers of both hemispheres is the cerebral cortex which covers the inner parts of the brain (3mm thick) - is what seperates us from animals because the human cortex is much more developed.

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CONTINUED

The cortex of both hemispheres is further divided into 4 lobes. Each lobe is associated with diffrent functions.

  • At the back of the frontal lobe is the motor cortex which is invloved in regulating movement, damage to this area will result in loss of control over movement or paralysation. 
  • Parietal lobes is the somatosensory (which is seperated from the motor cortex by a valley called the central sulcus. This area processes sesnsory info e.g. touch, heat, pressure. The amount of somatosensory area devoted to a particular body part denotes its sensitivity.
  • The visual area is in the occipital lobe. Info sent from right visual field to left visual cortex. So damage to the left hemisphere could produce blindless in the right visual field.
  • The temporal lobes house the auditory area. Which analyses speech absed info. Damage may produce partial hearing loss.

Language is restircted to the left side of the brain in most people. Broca, a surgeon, identified a small area in the left frontal lobe respponsible for speech production. Damage to Brocas area will cause Brocas aphasia and result in speech that is slow and lacks fluency. Werncike identified a region, Wernickes area in the left temporal lobe as being responsible for language comprehension -  so the speech they produced was fluent but meaningless.

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EVALUATION OF LOCALISATION

Brain scan evidence  - Peterson 1988 used brain scans to demonstrate how Wernickes area was active during a listening task and Brocas area was active during a reading task suggesting the areas have diffrent functions.  A long-term memory study by Tulving 1994 revelaed that semantic and episodic memories reside in diffrent parts of the prefrontal cortex. 

Neurosurgical evidence -  Dougherty reported 44 OCD patients who has undergone a cingultomy -  a neurosurgical procedure that involved lesioning of the cingulate gyrus. After 32 weeks, 1/3 had met the criteia for a successful response to the surgery and 14% for a apartial response.                                                                                                                          Case study evidence - Phineas Gage worked on a rail road. he dropped his tamping iron ontot he rock causing the explosives to ignite. The explosion hurled the 1m length pole through Gages left cheeck, passing behind his left eye and into the left frontal lobe. He turned from someone who was calm and rserved to someone who was quick-temepered and rude. So suggests frontal lobr may be responsible for regulating mood.

Lashleys research - He suggested that high cognitve functions such as learning are not localised but distributed in a more holistic way in the brian. Lashley removed areas of the cortex (between 10 and 50%) in rats that were learning a maze. No area was proven to be more important than any other when the rats were trying to learn the maze.  The processs seemed to require every part of the cortex. Which suggests that learning is too complex and requires the involvment of the whole brain.                                                                                                                                                                             Plasticity - Another argument against localisation is platicity. When the brain is dmaged a paricular function is lost, the rest of the brain appears to be able to recognise itself in ana attempt to recover the lost function. Lashley describes this as the law of equipotentially whereby surving brain circuits chip in so the same seurological function can be achieved.

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PLASTICITY AND FUNCTIONAL RECOVERY

Plasticity describes the brains tendency to change and adapt as a result of experience and new learning.

During infancy, hte brain experiences a rapid growth in the number of synaptic connections it has (approx 15,000 at age 2-3 years). As weage, rarely used connections are deleted and frqeuntly used connections are strenghtened ( synaptic pruning). It was originally thought that such changes were restricted to the developing brain within the childhood. However research has shown that in anytime in life existing neural connections can change or new neural connections can be formed, as a result of learning and experience. 

Maguire studied the brains of taxi driver and found significantly more volume of grey matter in the posterio hippocampus than in a control group. That part of the brain is associated with the development of spatial and navigational skills. Taxi drivers must complete 'The knowldge' test as part of training, which assess' their knowledge of possible routes. Tis learning experince alters the structure of the brain . Draganski imaged the brain of medical students 3 months before and after thier exams . Learning- induced changes were seen to have occured in the posterior hippocampus and the parietal cortex probs as a result of the exam.

The functional recovery that may occur in the brain after trauma is another example of plasticity. Healthy brain areas will takeover areas that are damaged. Neuroscientists suggest that this process can occur quickly after trauma and then slow down. 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 to enabling functioning to continue. This process is supported by the number of strcutural chnags in the brain including : Axonal sprouting - The growth ofnew nerve endings which connect with other undamaged nerve cells to form new neuronal pathways. Reformation of blood vessels. Recruitment of homologous area on the opposite side of the brain to perform specific tasks.

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EVALUATION OF PLASTICITY

Practical application - Contributed to the field of neurohabilitation.  Following an injury, spontaneous recovery tends to slow down after a number of weeks so forms of physical therapy maybe required to mantain improvements in functioning. Techniques may include movement therapy and electrical stimulation of the brain to counter the deficits in the motor and cognitive functioning.                                                                                                             Negative plasticity - The brains ability to rewire itself can have negative consequences e.g. drug use has been shown to result in poorer cognitive functioning as well as an increased risk of dementia in later life (Medina). Also 60-80% of amputees have been known to develop phantom limb syndrome (they think their missing limb is still there), this is unpleasent, painful and is thought to be due to cortical reorganisation in the somatosensory cortex that occurs as a result of limb loss. Ramachandran and Hirstein.

Age and plasticity - Functional plasticity tends to reduce with age. Bezzola demonstrted how 40 hours of golf training produced changes in the neural represenation of movement in participants aged 40-60. Using fMRI, the reserachers obsereved reduced motor cortex activity in golfers compared to the control group, suggesting more efficient neural represenations after training.

Support from animal studies - Hubel and Wiesel, sewed one eye of a kitten shut and analysed the brains cortical responses. It was found that the area of the visual cortex associated with the shut eye idle but continued to process info from the open eye.                                                                                                                                                 Evidence suggets persons education level may influence how well the brain functionally adapts after injury. Schneirder discovered that the more time brain injury patients spent in education - the greater their chances of a disability-free recovery (DFR). 2/5s of patients who achieved DFR had more than 16 years of education compared to 10% who had less than 12 years.

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SPLIT- BRAIN AND LATERALISATION

Hemispheric lateralisaton - The idea that the 2 hemispheres are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other e.g. language.  

Sperry's studied individuals with eplipsy who had undergone an opertaion called a commissurotomy - in which the corpus callosum which connects the 2 hemispheres is cut so communcation between the 2 hemispheres is removed. Sperry projected and image or word to the patients right visual field (left hemisphere) and same for the left visual field.

When a picture was shown to a patients right visual field, the patient could easily describe what was seen, however if the image was seen the the left visual field the patient could not desbribe it and normally said they saw nothing. This is because language is in the left-hemisphere so the right hemipshere cannot process language info.

The objects saw through the left visual field could be identified by touch using the left hand.

The right hemisphere processes visual spatial relations and the left processes language.

If 2 words were presented simultaneously, one of either side of the visual field e.g key on the left and ring on the right. the patient would writ ekey with their left handand say the word ring. The right hemisphere is also dominant in terms of recognising faces.

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EVALUATION OF SPLIT BRAIN

Demonstrated lateralised brain functions - Sperrys work into split brain has produced alot of reserach findings, the main conclusion being the left hemisphere is is more geraed towards analytical and verbal tasks and the right is spatial taks and music.  The left is the analyser whilst the right is the synthesiser.                                                                         Strengths of the methodology - The experiemnt made us of highly specialised and standardised procedures. Partcipants were asked to stare at a given point (fixation point), whilst one eye was blindfolded. The image projected would be shown for 1/10 th of a second meanin the split brain patient would not have time to move their eye across the image and so spread the info across both sides of the visual field and subsequently both sides of the brain. This allowed Sperry to ensure only one side of the brain was recieving info. Thus he developed a well controled procedure.                                                                                                                                                          Theoretical basis - Pucetti suggested that the 2 hemispheres are so functionally different that they represent a form of duality in the brain -  that in effect we are all in 2 minds ( and this situation is only emphasised in split brain patient). In contrats othe researchers have said the 2 hemispheres form a highyl intergrated system.                                                           Issues with generalisation - There were only 11 who took part in all variations of the basic procedure, all of whom had a history of epileptic seizures. It has been argued that this may have caused unique changes in the brain that may have influenced the findings. Also some particpants experienced more disconnection of the 2 hemispheres as part of their surgical procedure than tohers. Finally the control group mad eup of 11 people with no history of epilipsy may have been innappropriate.                                                                                                                                                          Differences in the function may be overstated - Modern neuroscientsist said the differences between the 2 hemispheres is less clear cut and more messy than what Sperry suggets.  In a normal brain the 2 hemisphere sare in constant communcation when performing everyday taks  and many of the behaviours associated with one hemipshere can be effectively performed by the other when the situation reuqires it. (plasticity).

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WAYS OF INVESTIGATING THE BRAIN

Functional magnetic resonance imaging  (fMRI) - It  works by detecting changes in blood oxygenation in specific parts of the brain. When a brain area is  more active it consumes more oxygen and to meet this demand blood  flow is directed to the active area (haemodynamic  response). It produces 3D  images showing which parts of the brain are involved in a particular process and this is important for our understanding of localistion of function.

Electroencephalogram (EEG) - Measures electrical activity within the brain via electrodes that are fixed to an individuals scalp using a skull  cap. The scan represents the brainwave patterns that are generated from the action of millions of neurons, providing an overall account of brain activity. EEG is ofetn used by clinicians as a diagnostic tool as unusual arythmic patterns of activity may indicate abonormalitie such as epilepsy.

Event-related potentials (ERP's) - EEG is a over general measure of brain activity, howver within EEG data contains all the neural responses associated with specific sensory, cognitive an motor events.  So researchers have developed have developed a way of teasing out and isolating these responses. Using a statistical averaging technique, all extraneous brain activity is  filtered out, leaving only the responses that relate to a specific stimulus.What remains are ERP's - types of brainwave that  are triggered by particular events.

Post-mortem examination - Analysis of a persons brain after their death. Normally to people who have rare disorders and have experienced unusual deficits in mental processes or behaviour during their lifetime. Areas of danage within the brain are examined after death to find a likely  cause of affliction.

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EVALUATION OF INVESTIGATING THE BRAIN

fMRI - Stengths- fMRI  doesnt rely on the use of radiation, and if administered correctly it is virtually risk free and straight foward to use.  It also  produces images that have a very high spatial resolution and provides a clear picture. Weakness - It is expensive and can  only capture a clear image if the person stays extreemly still. It has poor temporal resolution because there is a 5 second lag time behind the image on the screen and the firing of neuronal activity. 

EEG - Strengths - Provided the diagnosis of conditons such as epilipsy. It has contributed to much of our undertsanding of stages involved in sleep. It has high temporal resolution. Weakness -  It is overly general. It isnt useful forpinpointing the exact source of neural activity.

ERP - Strengths - This is much more specific and also have excellent temporal resolution, ecpsecially when comapred to fMRI, this has led to the precise measurement of cognitive functions.  Researchers have been able to identify many different types of ERP and describe its precise role e.g. P300 is thought to be involved in the allocation of attentional resources and the maintenance of the working memory. Weakness -  There is a lack of standardised methods which makes it difficult to confirm findings.  Also to establish pure data in ERP studies, backgroound noise  and extraneuous variables must be completely eliminated.

Post-mortems -  Strengths - Vital  in providing info for early understanding for processes in the brain e.g. Brocas area and Weknickes. Improves medical knowledge. Weakness - Causation is an issue because observed damage to the brain may  not be linked to the deficits under review but some other unrealte dtrauma. It also raises ethical issues such as constent e.g.HM wasnt able to  provide consent but research has been conducted on his brain.

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CIRCADIAN RHYTHMS

Biological rhythms are patterns of changes in body activity that conform to cyclical time periods.  Theyare influenced by internal body clocks  (endogenous pacemakers) as well as external changes to the environment ( exogeneous zeitgebers). Some of these rythms occurs many times during the day (ultradian rhythm). Others take longer than a day to complete  (infradian rhythms). Circadian rhythms are those which last for 24 hours e.g. sleep/wake cycle and core body temp.

The fact that we feel drowsy during the night and alert during the day demonstartes the effect of daylight (exogeneous zeitgebers).If we had no idea if it was day or nigth would we still fall asleep and wake up at regular times. Siffre spent extended periods underground to study effects on his own biological rhythms. Deprived of  exposure to natural light and sound. After 2 months in the caves of Southern Alps and then after in a Texan cave. His biologicl system settled down to one that was just beyond the usual 24 hours (about 25 hours) - he did continue to fall asleep and wake up on a regular schedule.

Aschoff and Wever convinced particpants to spend 4 weeks in ww2 bunkers deprived of natural light. All but one participant displayed a circadian rhythm between 24 and 25 hours. Both these studies suggests that the natural sleep/wake cycle is slightly longer than 24 hours but that  is entrained by exogenous zeitgebers associated with our 24 hours ( number of daylight hours, typical meal times etc). Fardolk studied a group of 12 people who lived in a dark cave for 3 weeks, going tobed when it was 11:45 and getting up at 7:45. Over the course of the study researchers sped up the clock so a 24 hour day only lasted 22 hours.This would suggest the existence of a strong free running circadian rhythm that cannot easily be overidden by changes in the environment.

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EVALUATION OF CIRCADIAN RHYTHMS

Practical application -  Given researchersa better understanding of the adverse consequences that occur as a resultof their disruption. e.g. night workers experienced a period of reduced concentration around 6 in the morning meaning mistakes and accidents are more likely (Boivin). Reserahc also suggests a relationship  between shift work and poor healt, shift workers are 3 times more likely to develop heart disease (Knutsson).  Thus research may have economic implication in terms of how to best manage productivity.

Drug  treatments - Circadian rhytyms coordinate a numbe rof the bodys processes e.g. heart rate, digestion.  This in turn has an effect on the action of drugs in the body and how well they are abosrbed. Research showed that there are certain peak times to when drugs are likely to be most effective. This has led to development of guidlines to do with timing of drugs (Baraldo).

Use of case studies and small samples-    Studies of  sleep/wake cycle  involved a small group of particpants. This  sint represnetative of the wider population and limits the extent to which generalisations can be made.  Siffre at age 60 observed that his internal clock ticked mych slowly than when he was younger.

Poor control in studies - Particpants still had acess to artificial light. e.g. Sriffe turned on a lamp everytime he woke up which remianed on until he went to bed. Czeisler was able to adjust participants circaidan rhythms from 22 to 28 hours using dim lighting.

Individual differences - Jeanne revealed that some people display a natural preference of going to bed early and waking up early and others going late and waking up late.  There  are also age differences in sleep and wake patterns.

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INFRADIAN AND ULTRADIAN RHYTHMS

The menstural cycle is an example of infradian rhythms, the cycle refers to the time between the first day of a womens period to the day before her next one.  Take approx 28 days to  complete this cycle.During each cycle, a rise in the level  of oestrogen causes the ovary to develop  an egg and release it (ovulation). After ovulation, progesterone helps the womb lining to grow thicker, readying the body for pregnancy, if pregnancy does not occur, the egg is absorbed into the body, the womb lining comes away and leaves the body ( menstural  flow).

Althought the mesntural cycle is an endogenous system, evidence suggests that it may be influenced by exogenous factors such as the cycles of others.  McClinktock involved 29 women with irregular periods. Samples ofpheromones were gathered from 9 of the women at different stages of their cyclevia cotton pads in their armpits. The pads were treated with alcohola nd frozen, to be rubbed on the upper lip of other particpants.  Found that 68% of women experienced changes to thier cycle which brought them colser to their odour donor.

Seasonal affective disorer  (SAD) -  A  mental disorder, main sysmtoms are low mood, lack of activity.  Symtptoms are triggered in the winter motnhs when number of daylight hours become shorter. SAD is a particular type  of infradian rhythms called a circannual rhythm as it is a yearly cycle.

Ultradian rhytyms (multiple times in 1 hour) stages of sleep. 5 distinct stages which span 90 minutes , a cycle that continues throughtout the night. Monitered usingEEG, Stage 1 and 2 -  a light sleep, brainwave patterns beome more slower and rhytmic (alpha waves). Satge 3 and 4 - Involve   delta waves which are slower . This is deep sleep. Stage 5 - REM sleep, the body is paralysedyet brain activity speeds up  significantly in a manner that assesmbles the awake brain, dreaming usually occurs in this stage.  Cycle is stage 1,2,3,4,3,3 and then REM. The closer you get to morning the less time spent in slow wave sleep(stage 3 and 4) and more time in REM.  Research uses EEG -brain wave. EOG - eye movement and EMG - muscle movement,  this helps us know what stage of sleep you are in. 

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EVALUATION OF INFRADIANA DN ULTRADIAN

Evolutionary psychologists claim that the synchronised menstrual cycle provides an evolutionary advantage for groups of women, as the synchronisation of pregnancies means that childcare can be shared among multiple mothers who have children at the same time.

Methodological limitations - Many factors which effect change in a womens menstrual cycle including stress, exercise - cofounding variables. This means that any supposed pattern of synchronisation is no more than would have been expected by chance. Research typically involves small samples and relies on particpants self- reporting. Trevathan failed to find any evidence of menstural synchrony in all female samples.

Evidence for stages in sleep - Dement and Kleitman monitered sleeping patterns in 9 partipcnats in a sleep lab. Brainwave activity was recorded on an EEG and the resulst were  highly controlled. REM activity in the brain was highly correlated with the experience of dreaming.

Practical apllication SAD - Effective treatment is phototherapy. Which is a lightbox that stimulates very strong light in the morning and evening, it is thought to reset melatonin levels. This  releives sysptoms in upto 6o% of sufferers  (Eastman). Howver the same study recorded a placebo effect of 30% using a sham-ion generator. This cats doubts on the chemical influence of phototherapy.

The EEG, EOG and EMG are objective measures, less vunerable to researcher bias and subjectivity. Self report measure is when the particpant says if they are dreaming or not, this is subjective because they could say it because of demand charcteristics. Research is conducted in sleep laboratorys, this is artificial also because the particpants are wired up to machines and this may affect sleeping patterns so low external validity. The individual differences because there are variations since some people do not sleep as well as others.

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ENDOGENOUS AND EXOGENOUS

Endogenous - The SCN is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere, it is influential in mantaining circadian rhythms such as the sleep/wake cycle. Nerve fibers are connected to the eye in an area called the optic chiasm on thier way to the the visual area of the cerebral cortex. The SCN lies just above the optic chiasm. The SCN passes the info on light that it receives to the pineal gland, this increases the production of a hormone called melantonin (a chemical that induces sleep) so slowly our brain activity falls  and then we go into a sleep.

Animal studies and the SCN - DeCoursey destroyed the SCN connections in the brain of 30 chipmunks who were then reurned to thier natural habitat and observed for 80 days. The sleep wake cycle of the chipmunks disappeared and by the end of the study a sig proportion of them had been killed by predators. Ralph bred hamsters with a 20 hour sleep wake cycle. When SCN

Exogenous zeitgebers are external factors in the environment.  Light - Light can reset the SCN and thus plays a role in the mantenance of the sleep wake cycle. Light also has an indrect influence on key processes in the body such as functions as hormone secretion and blood circulation. Campbell and Murphy demonstarted that light may be detecyted by skin receptor sites on the body even when the saem info is not recieved by the eyes. 15 participants were woken at varius times and a light was shone on the back of their knees. The researchers managed to produce a deviation in the participants usual sleep/wake cycle of up to 3 hours.

Social cues - At about 6 weeks the circadian rhythm begins . The schedule impose by parents are a key influence because of the determined meal times and bedtimes. Researchers also suggets that adpting to local times of eating and sleeping rather than responding to ones own feelings of hunger and fatigue, is an effective way of entraining the circadian rhythm and beating jet lag.

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EVALUATION

Ethics in animals studies - You cannot generalise the findings of these animal studies to humans. The DeCoursey study, involved the animals being exposed to considerable harm and subsequent risk when they returned to their natural habitat.

Influence of exogenous zeitgebers may be overstated - Miles recouned the story of a young man who was blind from birth and had a circaidan rhythm of 24.9 hours. Despite exposure to social cues, his cycle could not be adjusted and then had to take sedatives at night and stimulants in the morning to keep up with the 24 hour world. Also in artic region (where the sun does not set in summer) shows normal sleep patterns despite the prolonged exposure to light.

Methodological issues - The findings from Cambell and Murphy study has not been replicated. Other psyhcologists have suggested that there may have been some limited light exposure to the participants eyes (cofounding variable). Also just isolating light in this way does not give us insight into the many other zeitgerbers that influence the sleep wake cycle.

Interactionist system - Only in some circumstances are endogenous unaffected by the influence of exogenous. Total isolation studies such as Siffres cave study, are extremely rare and could be judged as lacking validity.

Beyond the master clock - There are many circadian systems in many organs and cells of the body - called peripheral oscillators - are found in the adrenal gland, oesophagus, lungs, liver, pancreas, spleen, thymus and skin. Although these peripheral clocks are highly influenced by the actions of the SCN, they act independently. Damiola demonstarted how changing feeing patterns of mice could alter their circadian rtyhtm by up to 12 hours, whilst leaving the rhythms of the SCN unaffected. Suggest their are other influences on sleep/wake cycle apart from SCN.

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