Biopsychology

Question 1

Outline the features of the nervous system (6 marks)

Answer 1

1. Human Nervous system = body wide system of nerve cells, directs body organs and muscles via the transmission of electro chemical messages, and collects and responds to information from the environment
2. Central Nervous System = includes brain and spinal cord
   - Brain - all conscious and most unconscious processing, includes cerebral cortex (gives us higher functioning than other animals)
   - The spinal cord which receives and transmits information and some reflex processing
3. Peripheral nervous system = relays and receive messages to the CNS through neurones to transmit messages
4. Somatic nervous system = controls voluntary movement and deals with the external environment
5. Autonomic nervous system = controls involuntary body responses and deals with internal environment
6. Parasympathetic nervous system = controls homeostasis and body at rest and is responsible for bodys ‘rest and digest’ function
7. Sympathetic nervous system = controls the body’s responses to a perceived threat and is responsible for the ‘fight or flight’ response

Question 2

Outline the function of 2 or more glands in the endocrine system (6 marks)

Answer 2

1. Pituitary gland (ACTH) (master gland) controls the release of hormones from other glands
2. Hypothalamus (CRH) = links nervous system to endocrine system
3. Pineal gland (Melatonin) = modulates sleep pattern, keep body to a day/night rhythm
4. Thyroid gland (Thyroxine) = modulates metabolism
5. Thymus gland (Thymosin) = stimulates development of T cells in the immune system
6. Pancreas (Insulin) = regulates blood sugar levels
7. Adrenal gland (Adrenaline) = regulates fight or flight

Question 3

What is the stress response?

Answer 3

Physical and psychological response when a person cannot cope with a stressor.

Uses endocrine and nervous system - adaptive as it aids survival

Uses sympathetic nervous system - shuts down non essential body actions + enhances essential ones

Afterwards the parasympathetic nervous system restores body levels to normal

Acute stress is dealt with by the Sympathetic adrenal medullary system (SAM system)

Question 4

What is the fight or flight mechanism?

Answer 4

1. Stressor detected by Hypothalamus
2. Sympathetic nervous system
3. Activates Adrenal Medulla
4. Produces adrenaline
5. At the same time the pituitary gland releases ACTH which stimulated the adrenal cortex to release cortisol
6. Stimulates changes throughout body - ‘fight or flight’ response
7. Parasympathetic nervous system restores body to normal resting when stressor subsides

Question 5

Outline the structure and function of three neurons (6 marks)

Answer 5

1. Sensory = detect sensations at sensory receptors, electrical signal converted into chemical signal to cross the synapse
2. Relay = action potential forms in dendrites (neurone is in the spine), sends signal to CNS and along axon to motor neurone
3. Motor = detects signal from relay neurone via synaptic transmission and passes signal along own mye

Sensory Neurons:
Structure:
Sensory neurons have long, thin dendrites that are highly sensitive to specific stimuli (e.g., light, sound, touch) and a relatively short axon that carries the signal to the CNS.

Function:
They receive sensory information from the environment and relay it to the brain and spinal cord, where it is processed and interpreted as sensations.

Relay Neurons:
Structure:
Relay neurons, also known as interneurons, are found in the CNS and have shorter dendrites and axons compared to sensory or motor neurons.

Function:
They act as a link between sensory neurons and motor neurons, facilitating communication and enabling reflexes and more complex neural pathways.

Motor Neurons:
Structure:
Motor neurons have short dendrites and long, thick axons that extend from the CNS to muscles.

Function:
They carry motor commands from the CNS to muscles, causing them to contract or relax, thus enabling voluntary and involuntary movements.

Question 6

Outline the process of synaptic transmission (6 marks)

Answer 6

1. Nerve impulse travels down an axon of a pre synaptic neurone
2. Nerve impulse reaches a synaptic terminal at the end of the pre-synaptic neurone
3. the neurotransmitters travel across the synapse
4. this triggers the neurotransmitters to move to the edge of the membrane of the pre-synaptic neurone
5. the neurotransmitters are released into the synaptic gap/cleft
6. the neurotransmitter then binds to receptors on the post synaptic neuron
7. this triggers the electrical signal to be sent down the post synaptic neurone
8. the neurotransmitters left in the synapse are then taken back by the presynaptic neuron
9. the vesicles in the pre-synaptic neuron will be refilled with neurotransmitter ready for the next electrical signal to occur

Neurotransmitters are excitatory = stimulate/make more likely, or inhibitory (make less likely)

Excitation = increase the likeyhood of a new action potential forming in the post synaptic cell - when detected by receptors the electrical charge inside becomes more positive and likely to fire - depolarisation

Inhibition = decrease the likleyhod of a new action potential forming in the post synaptic cell - when detected by receptors the electrical charge becomes negative and less likely to fire - hyper polarisation

Summation = combined effect of all inhibitory and all excitatory influences resulting in a new action potential forming or not

Uni-directional = information can only be passed between the pre and post synaptic neurone in one direction - this is due to the structure of the synapse such as the location of neurotransmitters (pre) and receptors (post)

Question 7

Discuss localisation of function in the brain (16 marks)

Answer 7

A01:
Localisation of function = The idea that different parts of the brain perform different tasks

Contralateral:
Left hemisphere = Activity on the right side of the body
Right hemisphere = Activity on the left side of the body

What does the frontal lobe do?
Front of brain
Deals with logic, planning, decision making, emotions, problem solving, impulse control

What does the parietal lobe do?
Top of the head
Deals with orientation, recognition, processing sensory information

What does the temporal lobe do?
Side of the head
Deals with hearing, processing auditory information, turns words into sounds, damage to area can lead to hearing loss or problems with language comprehension, contains auditory area which analyses speech

What does the occipital lobe do?
Back of the head
Deals with visual processing - ipsilateral and contralateral (right goes to left side of both eyes and left goes to right side of each eye

What does the motor area do?
Strip down back of frontal lobe in both hemispheres
Deals with controlling voluntary movement in opposite side of the body, damage to area may result in a loss of fine motor movements

What does the somatosensory area do?
Strip in the front of both parietal lobes
Deals with sensory information from the skin E.g touch, heat, pressure is represented

Broca’s area = Main centre of speech production (Left hemisphere)
Broca’s aphasia = cannot produce fluent speech but can comprehend speech

Wernicke’s area = Main centre of speech comprehension (Left hemisphere)
Patients with damage to Wernickes area can produce fluent speech but cannot comprehend speech

A03:
- Lashleys rats = removed 10-50% of the brain, then taught them to learn a maze, found no area was was more or less important in ability to learn maze, learning uses every part of the cortex, rather than being confined to a specific area - supports the holistic theory as it shows learning is too complex to put it down to one specific part - higher cognitive function

+ brain scan evidence showed Broca’s area was active during reading, Wernickes area active during listening = high internal validity
Also found semantic and episodic memories reside in different parts of the pre-frontal cortex

+ Phineas Gage - trauma to frontal lobe due to rail road spike through cheek and out of head = became angry and fitful. Supports localisation of function as he could still perform basic functions - movements and speech

• Plasticity - functions of area damaged can be recovered by different parts of brain = suggests more holistic approach rather than each part having individual function

Question 8

Discuss research into hemispheric lateralisation (16 marks)

Answer 8

A01:
Hemispheric lateralisation = The idea that the two halves of the brain are functionally different - certain functions are controlled by one hemisphere

Language = left (lateralised)

Motor area = not lateralised but cross wired/contralateral wiring

Vision = Vision is not lateralised
Contralateral and Ipsilateral (opposite and same sided)
each eye gets information from both the right visual field (RVF) and left visual field (LVF)
All information in the RVF goes to the left hemisphere and all information from the LVF goes to the right hemisphere

Who is Roger Sperry?
Nobel prize for work 1981
conducted studies on individuals who had undergone the same surgical procedure - a cerebral commissurotomy/Corpus Callosotomy (tissues which connect two sides of brain were cut down the middle)
individuals had two separate brains
procedure done to control severe epileptic seizures - stops shocks passing between the two hemispheres
Allowed Sperry to see the extent to which the two hemispheres were specialised for certain functions

Study:
- Image or word projected to patients right visual field and a different one to left visual field
- patient fixate on cross in middle of screen
- tested procedure on 11 patients who had already had their corpus collosum cut

1. Patients had to describe what they saw = RVF patient could describe as left hemisphere responsible for language, LVF patient said nothing there as they could not describe it
2. Recognition by touch = although they could not say what they saw, they could select the correct object using their left hand (controlled by right hemisphere) from behind a screen
   Therefore could not verbally identify the word but could still understand what it was using Right hemisphere
   Could also pick closely matching objects E.g pick ashtray when shown picture of cigarette to LVF
3. Draw what they saw

Findings:
Left hemisphere is verbal, right is non-verbal
right hemisphere can process images and match up objects (non-verbally)
When shown racy image to LVF person would giggle/blush (emotional reaction) showing that the RH processes emotion even when the person says they saw nothing

A03:
+ Fink’s brain scans (PET) show different areas are active during a visual task = when participants looked at whole picture the RH is more active, but when asked to focus on specific detail the LH was more dominant
Shows the LH and RH have different functions even in connected brains

+ adaptive advantages to split/lateralised brain = Gazzaniga found split brain patients performed better on certain tasks - E.g identifying odd one out due to LH having better cognitive abilities, and in split brain patients it is not interfered with by the RH

+ Roger found lateralised chickens could find food whilst watching for predators but normal chickens couldn’t
Shows it can be an advantage in animals as well as humans

+ Sperry’s work was standardised and scientific = participants given a ‘fixation point’ to stare at during the task and also the image only flashed up for a tenth of a second, Sperry could make sure it was only being received/processed by one hemisphere rather than it being share by both
This is a strength because it has high internal validity and replicability

• Lack of generalisability with Sperry’s work = split brain patients are rare (just 11 males tested, small sample size), all had epilepsy so potential underlying damage in brains caused by the shocks, control group were non-epileptic so comparison is different
  Limitation as it is not representative of normal brains, therefore not generalisable to wider population, ultimately doesn’t tell us a lot about hemispheric lateralisation

Question 9

Discuss plasticity and functional recovery in the brain (16 marks)

Answer 9

A01:
Plasticity = The brains ability to change and adapt based on experience and new learning

Functional recovery = A form of plasticity which occurs after trauma or damage to the brain. The brain can redistribute or transfer functions that are usually performed by the damaged area to other undamaged areas. Healthy brain areas or tissues appear to be able to take over the functions of areas that are destroyed or missing.

What happens during brain recovery?
1. Brain rewires/reorganises itself by forming new synaptic connections close to the area of damage
2. secondary neural pathways are activated or ‘unmasked’ that enable functioning to occur similar to before = Doidge

other structural changes in the brain include:
1. Axonal sprouting: Brain grows new nerve endings which connect to form new neural pathways
2. Denervation super sensitivity: axons that do a similar job become aroused to a higher level to compensate for lost ones = can result in pain
3. Recruitment of homologous areas: this is where similar areas on opposite sides of the brain are recruited to perform tasks E.g Broca’s area may move to the right

Example:
Jody
Had epileptic seizures
had surgery, half brain taken out (right side)
within in 10 days she could walk again (LH made new connections)
slight paralysis in left hand but functions

Study: Maguire
Studied brains of taxi drivers using MRI scanners
Found they had more matter in their posterior hippocampus than a control group
Part of their brain was involved in spatial navigation
London cabbies test called ‘the knowledge’
Longer they had been doing the job = more pronounced structural difference - positive correlation

However, does not test the size of their posterior hippocampus before becoming a taxi driver, therefore can’t be sure the difference is due to ‘the knowledge’. Could have been taxi drivers due to already existing difference

Other supporting study
Draganski = imaged brains of medical students 3 months before and after their medical exams and found learning induced changes (larger and more connections) in the posterior hippocampus and parietal cortex
Mechelli found a larger parietal cortex in the brains of people who were bi-lingual in comparison to mono-lingual matched controls

This shows when we experience learning, out brain adapts and changes as a result of new experiences and new learned content/knowledge - makes new connections

A03:
P - Not all plasticity and functional recovery is a good thing. There are sometimes negative consequences to the brain re-wiring itself
E - 60-80% of amputees may suffer from phantom limb syndrome - where a person continues to experience sensations in a missing limb
E - May be due to cortical reorganisation in the somatosensory cortex that occurs as a result of limb loss
L - Can cause lifetime pain/unhappiness and suffering

P - Good practical application
E - neurohabilitation - techniques such as physical and movement therapy and electrical stimulation of the brain may help the brain to ‘fix itself’
E - ‘constraint movement therapy’ - stroke patients = repeatedly try and use affected part of body E.g lift arm whilst unaffected arm is restrained
L - This is a strength because it has positive effects that can help people recover from injuries

P - plasticity can occur throughout your whole life time
E - Bezzola conducted study on novice golfers = gave people aged 40-60 who had never played golf 40 hours of training and scanned their brains using FMRI scanner both before and after the training
E - Found increased motor cortex activity compared to long term golfers
L - supports idea of plasticity and shows it is not limited to young developing brains, but that learning and experiences which occur throughout a lifetime can affect the structure of the brain

P - There is animal evidence of plasticity and functional recovery
E - Hubel and Wiesel sewed one eye of a kitten shut and analysed the brains cortical responses
E - The side of the visual cortex associated with the shut eye would process information from the other eye
L - This shows us that, at least in animals, inactive brain areas can change and adapt to take on new functions after damage

P - The greater your ‘cognitive reserve ‘ the better your brain will recover from brain injury
E - study found that the longer brain injury patients had spent in education, the better chance of recovery. 40% of the patients who recovered fully from their brain injury had spent more than 16 years in education. In comparison just 10% of the patients who recovered fully had spent 12 years in education
E - This shows that the more the brain is practising plasticity the better it can recover later in life
L - Highlights how factors such as education may impact the chances of successful recovery. We can also question whether there might be other factors such as gender, health or activity levels which also impact the likelihood of functional recovery

Question 10

Discuss two or more ways of studying the brain (16 marks)

Answer 10

1. FMRI (Functional magnetic resonance imaging)

• Measures changes in brain activity while a person performs a task
• Does this by measuring changes in blood flow in particular areas of the brain which indicates neural activity in these areas - measures blood flow using radio waves and a magnetic field,
• if part of brain is active, there is an increased demand for oxygen in that area
• so increased blood flow and delivery of oxygen in the red blood cells
• researchers can produce maps showing which areas of the brain are involved in a particular mental activity
• The resulting FMRI data can then be used to identify the brain areas where there is a matching pattern of change. As a result of this data it can be conducted that these areas have been activated by the stimulus in question

FMRI:
Strengths
+ unlike other scans (such as PET scans) it doesn’t rely on the use of a radioactive tracer. Therefore, it is risk free and non - invasive.
+ it produces high resolution images that are accurate to the millimetre so it provides psychologists with a clear image of where functions are located
- The machines are expensive (over 1 mill to buy) compared to other imaging techniques - requires equipment and trained experts. Very costly for the NHS to use and run
- It requires patient to stay still for a clear image which wouldn’t be easy for patients with some conditions (E.G children, elderly, those with disabilities)
- FMRI is an indirect measure of functioning. It is studying blood flow rather than the actual firing of neurones. As such there is a 5 second delay between the neurone firing and activity being detected (due to the time it takes oxygen to reach the brain. This means that what you’re seeing isn’t quite real time (it has poor temporal resolution.

2. EEG (Electroencephalogram)
   - measures electrical activity in the brain through electrodes placed on scalp which detect small electrical charges resulting from the activity of brain cells. When electrical signals from the different electrodes are graphed over a period of time, the resulting representation is called an EEG
   - the data can be used to detect various types of brain disorders or to diagnose other disorders that influence brain activity such as Alzheimers disease
   - EEG is often used by clinicians as a diagnostic tool to look for unusual patterns of activity which may suggest neurological abnormalities such as tumours

EEG:
Strengths
+ has been extremely useful in investigating a wide range of issues including epilepsy and sleep disorders/patterns
+high temporal resolution (as it can detect electrical activity in under one millisecond)
- It is a general measure 0 it can only show groups of neurons firing, it is not strong enough to pick up small signals from individual neurons
- It does not allow researchers to differentiate when different but adjacent (next to) areas are firing

3. ERP (Event related potentials)
   - Too crude and general in raw form
   - uses same technique as EEG but presents a stimulus many times
   - creating a smooth curve of activation by combining the data in a process called statistical averaging
   - This removes background electrical noise unrelated to the stimulus, all that is left is event related potentials
   - The waveform’s peaks and dips show exactly when cognitive processes in the Brian happen after the stimulus is presented

ERP’s
Strengths
+ more specific than raw EEG readings
+ ERP’s are derived from EEG data so they also have excellent temporal resolution
- Differing procedures have been adopted across different research institutions (not standardised, so it is difficult to compare and replicate the findings of studies using this technique)
- To be successful all extraneous interference needs to be eliminated and this is hard to achieve

4. Post Mortem Examinations
   - used to establish the underlying neurobiology of a particular behaviour
   - researchers may study a person who displays an interesting behaviour while they’re alive that might suggest underlying brain damage
   - Subsequently, when a person dies, unusual brains are dissected such as brains that suffered trauma, or from individuals with mental illness
   - researchers can look for abnormalities that might explain that behaviour and which are not found in control individuals
   - Early example of this was Broca’s work with Tan, who displayed speech problems (could only say Tan due to expressive aphasia)
   - He found that there was damage/a lesion in an area of the frontal lobe after Tan’s death - which is now known as the ‘Broca’s area’; an important area for speech production

Post Mortems:
Strengths
+ vital during the early days of psychology before technology was developed E.G Broca and Wernicke
+ Post - mortems improve medical knowledge and help generate hypothesis for further study
- Cause and effect is a problem - the differences observed in a dead brain may be unrelated to the behavioural symptom a person showed when they were alive. We have to infer causality
- Informed consent - some patients lose the ability to consent during their lifetime due to the issues that make them of interest (HM) to but even those that don’t have these issues are problematic because consent is needed from relatives (and needed quickly)

Question 11

Discuss two or more biological rhythms (16 marks)

Answer 11

A01:
1. Circadian = sleep/wake, once a day/24 hours

Pattern of changes in body activity that conform to cyclical time periods

Influenced by internal body clocks (endogenous pacemakers) or external changes in/to the environment (exogenous zeitgebers)

Sleep/wake cycle = Alert during day due to sunlight (exogenous zeitgeber) and due to internal body clock (endogenous pacemaker) /(suprachiasmatic nucleus (SCN)) - lies above optic chasm so provides info from eye about light (light can reset the SCN)

Study: Siffre
Spent 2 months in cave in Alps and 6 months in cave in Texas
Found his natural ‘free running’ biological rhythm settled to roughly 24-25 hours - fell asleep and woke up on regular schedule

Tells us endogenous pacemakers control our sleep/wake cycle and naturally 24/25 hours. However, external factors can affect it (daylight/meal times)

Supporting study: Aschoff and Wever
Got participants to spend 4 weeks in a WWII bunker deprived of natural light
Found they all displayed natural rhythm of 24-25 hours
Normal day to day life limits us to just over 24 due to daylight hours and meal times (exogenous zeitgebers)

Another supporting study: Folkard
Participants live in cave for 3 weeks
Go to bed 11:45 and wake 7:45
experimenters sped up clock so 24 hours was 22 hours
participants natural biological rhythms could not adjust and remained on a 24 hour cycle - endogenous pacemaker cannot be altered by environmental changes

Core body temp = Varies 2 degrees in the day
lowest around 4am (36 degrees)
Warmest around 6pm (38 degrees)

Evidence suggests body temp has effect on mental abilities = warmer we are, the better our cognitive abilities

Folkard found = Children read stories at 3pm showed greater recall and comprehension compared to those who read stories at 9am

A03:
+ Allows us to understand negative consequences of night work
night workers have reduced concentration = more accidents at 6am
night workers are 3x more likely to develop heart disease (only fast food open)
Therefore, research helps us to understand the economic implications of how best to manage shift work

• Not generalisable as Siffre study is small sample size and unrepresentative of wider population - found his internal clock was slower at 60 than when he was younger
• individual differences = some people go to bed early and rise early some people go to bed late and wake late, as well as age differences in need for sleep, can only create averages based on this data which may be potentially meaningless

2. Infradian = menstrual cycle, less than once a day

Example = Menstrual cycle

Process:
28 days
oestrogen levels rise cause the ovary to release an egg
progesterone helps to thicken womb lining - readying for pregnancy
If pregnancy does not occur, egg is absorbed and womb lining comes away (menstrual flow)

There is considerable variation - some women 23 day cycle, some 36 day cycle

Study: McClintock
Test if menstrual cycle is affected by other women’s pheromones (exogenous factors)

29 women participants with irregular periods
9 gave pheromone samples at various stages of the menstrual cycle through wearing cotton pad placed in armpit for 8 hours
Pads then rubbed on lips of 20 other women
Each day the 9 ‘donor’ women gave another sweat pad which was the rubbed on lip of other women
Found that students who spent extended time together tended to sychronise their menstrual cycles

68% women experienced changes in their cycles - brought them closer to cycle of ‘donor’, Shows menstrual cycle is affected by exogenous zeitgebers

Seasonal affective disorder (SAD) = Seasonal variation in mood

Depressed in winter due to daylight hours shorter

Infradian rhythm called a circannual rhythm (yearly cycle)
could be circadian rhythm as it may be due to lack of sleep/wake cycle due to long periods of darkness during winter

Melatonin which is secreted by pineal gland at night is partly responsible - lack of light during winter results in more melatonin secretion

This has a knock on affect on the production of serotonin in the brain - a chemical which has been linked to the onset of depressive symptoms

A03:
- as menstrual cycles vary in length, women can appear to synchronise just due to their variability in their cycles - something not taken into consideration during studies showing positive results

• study showed lesbian couples did not synchronise, countering McClintock’s theory

+ McClintock found women who lived in the same university dorm appeared to synchronise their cycles with their friendship groups - suggesting menstrual cycle infradian rhythm synchronises

• humans cannot detect pheromones, only a common messaging system in animals - not accepted among scientists

3. Ultradian = light and deep sleep, more than
   once every 24 hours

Example = The stages of sleep

1. Light sleep = can be easily woken, brain waves high frequency, short amplitude (Alpha)
2. Light/half sleep = sleep spindles - random changes in pattern of alpha waves, breathing/hearth rate slow, body temp decrease (Alpha)

3/4. Deep sleep = breathing/HR slow, limited muscle activity, difficult to wake someone, low frequency high amplitude
waves (Delta)

5. REM sleep = body paralysed, brain activity resembles awake brain, eyes occasionally move around, brain produces theta waves thus rapid eye movement (REM), dreams most experienced in REM sleep but may also occur in deep sleep (Theta)

One cycle takes about 90 minutes

Groundbreaking research by Dement & Kleitman (1957) made the link between REM sleep and dreams
A sample of five participants were studied intensively
The participants were taken to a sleep lab
They had been told not to drink alcohol or caffeine before the experiment
An EEG machine was used to track their brainwaves during sleep
They were woken at specific intervals during their sleep and asked if they were dreaming and if so, what was the dream about
The findings showed a positive correlation between REM sleep and dreaming
The nature of the dreams was matched by their eye movements e.g.
vertical eye movements occurred with dreams of climbing ladders, watching climbers, and throwing basketballs in the air
horizontal eye movements occurred with dreams of watching people throw tomatoes at each other

A03:
+ Dement & Kleitman conducted a well-controlled study with extra care taken to eliminate possible confounding variables of alcohol or caffeine intake before the study

+ This means that their research is high in reliability
Subsequent replications of their sleep study have supported Dement & Kleitman’s findings
This gives good validity to the idea that REM sleep is associated strongly with dreaming

• A sample of five participants means that the findings are difficult to generalise
  This means that the findings lack external validity
  A larger sample would also increase the robustness of the data
• Dement & Kleitman carried out their research in the 1950s which means that it may lack temporal validity
  The use of digital technology such as smartphones, which did not exist at the time of the research, may interfere with people’s ultradian rhythms
  This means that new research should be conducted to investigate the extent to which REM and dreaming are linked

+ pratical applications in the development of technology and devices tracking and supporting individuals with sleep - leads to happier, healthier and more economically productive population

• individual differences of REM sleep - babies = 80% REM whilst adults = 20-25%
  Suggests stages of sleep isn’t simple process but adapts to the developmental needs of the individual

+ patients recovering from drug overdose showed increased REM sleep, suggesting REM is for mental recover

+ evolutionary advantage = ancestor females menstrual cycle sync = pregnant same time, allows babies who lose mother to have access to breast milk, improve chances of survival - supports synchronisation as an adaptive strategy

• Synchronisation is by chance due to factors such as stress, change in diet, exercise etc - act as confounding variables - might not learn anything from it (low internal validity

+- SAD treated with phototherapy - strong light in morning and evening = reset melatonin levels, relieved 60% of sufferers but study also recorded 30% placebo affect - low validity but potential treatment for SAD

Question 12

Discuss the role of endogenous pacemakers and exogenous zeitgebers in controlling biological rhythms (16 marks)

Answer 12

Internal body clocks = endogenous pacemakers
external changes in/to the environment = exogenous zeitgebers - reset biological clocks through entrainment

SCN = A type of endogenous pacemaker
Lies above Optic Chiasm
When it detects light it sends signal to pineal gland which stops production of melatonin which results in a sleep response

The SCN passes the information on day length and light that is received to the pineal gland ( a pea like structure in the brain). During the night the pineal gland increases production of melatonin (induces sleep) and is inhibited during periods of wakefulness.

Suprachiasmatic nucleus - biological clock, circadian pacemaker
Melatonin - only produced in the dark, light is detected by the SCN, SCN stops the pineal gland from producing melatonin

Study:
DeCoursey’s (2000) Chipmunks:
- Destroyed the SCN connection of 30 chipmunks
- They were then returned to the wild for 80 days
- Sleep wake cycle disappeared so by the end of the study most of them had been eaten as they were asleep at the wrong times

Ralph’s (1990) Hamsters:
- Bred mutant hamsters with a 20 hour sleep wake cycle
- When the SCN of the mutant hamsters was transplanted into 24 hour cycle hamsters, the cycle of the normal hamsters changed to 22 hours

Morgan (1995):
the researcher bred hamsters so that their circadian rhythms were 20 hours, rather than the usual 24-hour cycle
SCN neurons from the 20-hour hamsters were transplanted into the brains of normal hamsters,
the hamsters with transplanted SCN neurons went on to follow the same irregular 20-hour circadian rhythm as the original 20-hour cycle hamsters
thus, the transplanted SCN had imposed its irregular pattern onto the hamsters

the researcher concluded that the SCN is a significant endogenous pacemaker which is crucial to the proper functioning of circadian rhythms
these findings also demonstrate the importance of exogenous zeitgebers to the sleep-wake cycle (endogenous pacemakers and exogenous zeitgebers work hand-in-hand)

A03:
- Numerous circadian rhythms which can act independently = Limitation - this suggests that there may be many other complex influences on the sleep/wake cycle, aside from the master clock (the SCN)

• Siffre used artificial light which could have reset his biological clock = Limitation - this suggest the more researchers attempt to isolate the influence of internal pacemakers and exogenous zeitgebers = the lower the validity of the research, in everyday life IP and EZ interact
• Generalisability and Ethical harm caused to animals during testing = Limitation - whether what we learn from investigations such as these justifies the aversive procedures involved is a matter of debate
• People who live in the artic circle (little darkness in winter and light in summer) have similar sleep patterns all year round, despite spending around six months in almost total darkness = Limitation - this suggests that the sleep wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light

Miles found a blind man had rhythm of 24.9 hours, despite exposure to social cues his sleep/wake cycle could not be adjusted, had to take sedatives at night and stimulants in the morning to keep pace with the 24-hour world= Limitation - this suggests that social cues alone are not effective in resetting the biological rhythm