Brain Structure + Function

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Areas of the Brain

Cerebrum

  • is the largest part of the brain - divided into left + right cerebral hemispheres - which is involved in vision, learning, thinking and emotions
  • has a thin outer layer (cerebral cortex) which has a large surface area so it is highly folded to fit into the skull
  • different parts  are involved in different functions e.g. the back of the cortex is involved in vision and the front is involved in thinking

Cerebellum

  • is underneath the cerebrum and also has a folded cortex
  • is important for coordinating movement and balance
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Areas of the Brain

Hypothalamous

  • is found beneath the middle part of the brain
  • automatically maintains body temperature at its normal temperature (thermoregulation)
  • produces hormones that control the pituitary gland (that sits below the hypothalamous)

Medulla Oblongata

  • is at the base of the brain, at the top of the spinal chord
  • automatically controls breathing rate and heart rate
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Computed Tomography Scans

CT scanners use radiation (x-rays) to produce cross-section images of the brain. Dense structures absorb more radiation than less dense structures, so they show up as a lighter colour on the scan. CT Scans:

  • show the major structures in the brain
  • can be used to work out function - if a scan shows a diseased or damages brain structure and the patient has lost sme function, the function of that part of the brain can be worked out
  • can be used to diagnose medical problems  e.g. bleeding in the brain after a stroke (blood has a different density than brain tissue so it shows up a lighter colour, a scan will show the extent and location of the bleeding, which can be used to work out which blood vessels have been damaged and what brain functions are likely to be affected by the bleeding
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Magnetic Resonance Imaging

MRI scanners use a strong magnetic field and radio waves to produce cross-section images of the brain. MRI scans:

  • show detalied images of brain structure - you can clearly see the difference between normal and abnormal brain tissue
  • can be used to investigate brain structure in the same way as CT scans
  • can be used to diagnose medical problems as they show damages or diseased areas of the brain e.g. brain tumors (tumor cells respond differently to a magnetic field than healthy cells so they show up as a lighter colour, the scan will show the exact size of the tumor and its location in the brain - doctors can use this information to decide the most effective treatment and work out what brain functionsmay be affected by the tumor)
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Functional Magnetic Resonance Imaging

fMRI scanners show changes in brain activity as they happen (more oxygenated blood flows to active areas of the brain to supply the neurones with oxygen and glucose and molecules in oxygenated blood respond differently to a magnetic field than those in deoxygenated blood, meaning more active areas of the brain can be identified). fMRI scans:

  • give a detailed picture of the brain's structure, similar to an MRI scan
  • are used to research the function of the brain - if a function is carried out whilst in the scanner, the part of the brain that's involved will be more active
  • are useful to diagnose medical problems as they show damaged or diseased areas of the brain and allow you to study conditions caused by abnormal brain activity (some conditions don't have an obvious structural cause) e.g. and fMRI scan can be taken of a patient's brain before and during a seizure (this can help pinpoint which part of the brain isn't working properly, and find the cause of the seizure - the patient can receive the most effective treatment)
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Brain Development

  • brain development is how the brain grows, and neurones connect together (measures include the size of the brain, the number of neurones it has, and the level of function - speech/intelligence - a person has)
  • the brain develops the way it does because of genes and the environment
  • nature and nurture are both involved in controlling brain development, but scientists disagree about which influences brain development the most
  • there are five methods used to investigat the effects of nature and nurture on brain development: animal experiments, newborn studies, twin studies, brain damage studies, and cross-cultural studies
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Animal Experiments

  • scientists study the effects of different environments on the brain development of animals of the same species - any differences in their brain development are more likely to be due to nature than nurture 
  • rats raised in a stimulating environment have larger brains and get better scores on problem-solving tasks than rats raised in boring environments, suggesting nurture plays a large role in brain size and evelopment of problem-solving skills. rats reared in isolation have similar brain abnormalities to those found in schizophrenic patients, suggesting nurture plays a lrge role in brain development
  • scientists also study the effects of different genes on the brain development of animals raised in similar environments - they ususally do this by genetically engineering mice to lack a particular gene, any differences between the brain development of the genetically engineered mice and normal mice are more likely to be due to nature than nurture 
  • mice engineered to lack the Lgl1 gene develop enlarged brain regions and fluid builds up in their brains, suggesting nature plays a large role in brain development
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Newborn Studies

  • the brain of a newborn baby hasn't been affected by the outside environment
  • scientists study the brains of newborn babies to see what functions they're born with, and how developed different parts of the brain are - what they're born with is more likely to be due to nature than nurture

newborn studies have shown that:

  • babies are born with a number of abilities (they can cry, feed, recognise a human face) suggesting that nature plays a large role in controlling these abilities
  • newborn babies don't have the ability to speak, suggesting nurture plays a large role in the ability to speak
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Twin Studies

  • identical twins are gentically identical - if they are raied separately, they'll have identical genes but different environments
  • scientists can compare the brain development of separated identical twins - any differences between them are due to nurture, and any similarities are due to nature
  • scientists also study the brain development of identical twins raised together (they are genetically identical and have similar environments) so are compared to non-identical twins (who are genetically different but have similar environments) that act as a control group to cancel out the influence of the environment, so any difference in brain development between identical and non-identical twins are more likely to be due to natre than nurture
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Twin Studies

  • identical twins have very similar IQ scores, sugesting nature plays a large role in intelligence
  • stuttering of both twins is more common in identical twins than in non-identical twins, suggesting nature plays a large role in developing the speech area of the brain
  • there's no difference in reading ability between paris of identical and non-identical twins, suggesting nurture plays a large role in reading ability
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Brain Damage Studies

  • damage to an adult's brain can lead to loss of brain function, it can't repair itself because it is already fullt developed, unlike a child's brain which is still developing - scientists can study the effects of brain damage on their development
  • to do this, scientists compare the development of a chosen function in children with and without brain damage - if the characteristic still develops in children with brian damage, then brain dvelopment is more likely to be due to nurture than nature for that characteristic
  • if the characteristic doesn't devlop in childrne with brain damage, then brain develpment is more likely to be due to nature for that characteristic
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Brain Damage Studies

  • children aged 1-3 who are born with damage to the area of the brain associated with language, show a delay in major language milestones (understanding words, producing sentences etc.) when compared to children born without brain damage
  • by age 5, thier language skills are the same as children with no brain damage - showing that if a young child's brain is damaged, they can still learn language
  • this suggests that nurture plays a large role in language development
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Cross-Cultural Studies

  • children brought up in different cultures have different environmental influences (social practices, beliefs, education, gneder influences etc.)
  • scientists can study the effects of a different upbringing in brain development by comparing large groups of children of the same age from different cultures
  • scientists look for major differences in characteristics - any differences in brain development detween different cultures are more likely to be due to nurutre, and similarities are more liekly to be due to nature
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Cross-Cultural Studies

  • Kenyan children who eat protein-rich foods (providong nutrients such as zinc and iron) have higher IQs than children who have a poor diet and limited protein, suggesting nurture planys a large role in intelligence
  • the mapping abilities (e.g. perspective drawing) of young children are well-developed across cultures, suggesting nature plays a large role in mapping abilities
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Habituation

  • animals (and humans) increase their chances of survival by responding to stimuli - however, if the stimuli is unimportant (neither threatening or rewarding) there's no point responding to it
  • if an unimportant stimulus is repeated over a period of time, an animal learns to ignore it - this reduced response is habituation (meaning animals don't waste time and energy respinding to unimportant stimuli)
  • animals still remain alert to important stimuli (which might threaten their survival)
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Habituation

investigating habituation

  • gently tap a tortoise on its shell - it should withdraw its head, feet and tail into its shell
  • time how longit takes for the tortoise to reappear out if its shell after you've tapped it
  • tap the tortoise's shell at regular intervals (e.g. every minute) and record how long it takes for it to reappear

if habituation has taken place the tortoise should reappear out of its shell quicker the more you repeat the stimulus, if it hasn't occurred the tortoise will take the same lenghth of time to reappear each time

the tortoise should still remain alert to an unfamiliar simulus

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Visual Cortex

  • the visual cortex is an area of the cerebral cortex at the back of the brain, its role is to receive and process visual information
  • neurones in the visual cortex reveive nformation from either the left or right eye, they are grouped together in columns called ocular dominance columns, the left and right ODCs are the same size and are arranged in an alternating pattern

the structure of the visual cortex was discovered by two scientists called Hubel and Wiesel - they used cats and monkeys to study electrical activity of neurones. they found that the left ocular dominance columns were stimulated when an animal used its left eye, and the right ocular dominance columns were stimulated when an animal used its right eye

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Visual Cortex

  • Hubel and Wiesel stitched shut one eye of each kitten so they could only see out of their other eye
  • the kittens were kept like this for several months before their eyes were unstitched
  • they found that the kitten's eye that had been stitched up was blind
  • they also found that ocular dominance columns for the stitched up eye were a lot smaller than normal, and the ODCs for the open eye were a lot bigger than normal - the ODCs for the open eye had expanded to take over the ither columns that weren't being stimulated - when this happens, the neurones in the visual cortex are said to have switched dominance
  • Hubel and Wiesel investigated if the same would happen in an adult's brain
  • they stitched shut one eye of each cat, who were kept like this for several months
  • when their eyes were unstitched, they found that the stitched eyes hadn't gone blind - the cats fully recovered thier vision and their ODCs remained the same
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Visual Cortex

  • Hubel ans Wiesel repeated the experiments on young and adult monkeys -  they saw the same results, which showed that the visual cortex only develops into normal left and right ocular dominant columns if both eyes are visually stimulated in the very early stages of life
  • their experiments on cats show there's a period in early life when it's critical that a kitten is exposed to visual stimuli for its visual cortex to develop properly (the critical 'window')
  • the human visual cortex is similar to cats, so Hubel and Wiesel's experiments provide evidence for a critical window in humans
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Critical Window

Scientists have investigated how the visual system develops in humans, e.g. by looking at cataracts in the eye:

  • a cataract makes the lens in the eye go cloudy, causing blurry vision
  • if a baby has a cataract, it's important to remove the cataract within the first few months of the baby's life - otherwise their visual system won't develop properly and their vision will be damaged for life
  • if an adult has a cataract then it's not as serious - when the cataract is removed, normal vision comes back straight away because the visual system is already developed
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Ethics

  • animals are different form humans, so drugs tested on animals may have different effects in humans
  • experiments can cause pain and distress to animals
  • there are alternatives to using animals in research e.g. using cultures of human cells or using computer models to predict the effects of experiments
  • some people think that animals have the right to not be experimented on e.g. animal rights activists
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Ethics

  • animals are similar to humans, so research has led to many medical breakthroughs e.g. antibiotics, insulin for diabetics, organ transplants
  • animal experiments are only done when it's absolutely necessary and scientists follow strict rules e.g. animals must be properly looked after and anaesthetics must be used to minimise pain
  • using animals is currently the only way to study how a drug affects the whole body - cell cultures and computers aren't a true representation of how cells may react when surrounded by other body tissues. it's also the obly way to study behaviour
  • some people think that humans have a greater right to life than animals because we have more complex brains
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