Localisation of function + Hemispheric lateralisation

• Localisation of function is the idea that different parts of the brain are responsible for different functions. This is supported by recent neuroimaging but also earlier via case studies.
• 4 Brain Lobes

  1. frontal = thinking, memory, behaviour, movement
  2. temporal = hearing, learning and feelings
  3. parietal = language and touch
  4. occipital = sight

  Cerebellum = balance and co-ordination

  Brain stem = breathing, heartrate and temperature
• Both hemispheres = motor cortex, somatosensory cortex, visual cortex, auditory cortex

  Left hemisphere only = Broca's area + Wernicke's

  Contra-lateral control = left hemisphere controls right side of the body and vice versa.
• • Motor area, frontal lobe, responsible for voluntary by sending signals to muscles in the body
  • Somatosensory area, parietal lobe, receives sensory info from skin to produce pressure, pain and temperature.
  • Visual area, occipital lobe, receives and processes visual info, colour and shape.
  • Auditory area, temporal lobe, analyses and processes acoustic info
  • Broca's area, left frontal lobe, responsible for speech production, Broca's aphasia slow + incoherent 'broken' speech
  • Wernicke's area, left temporal lobe, language processing/comprehension. Wernicke's aphasia speech is fluent but meaningless.
• AO3 Localisation of Function -

  • Individual differences not taken into account. Herasty found women have a proportionally larger Broca's and Wernicke's area than men. This may mean the concept has beta bias.
  • Case studies e.g. Phineas Gage are idiographic and cannot be generalised to everyone as they lack population validity. Although many case studies support the idea of Broca's aphasia - Patient Tan, Phineas Gage, Clive Wearing.
• AO3 - Localisation of Function

  • Biologically reductionist, reduces complex human behaviour and cognitive processes to one area. Too simplistic.
  • Use of neuroimaging supports the scientific method and uses empirical methodology to establish causal relationships.
• Plasticity + Functional Recovery -

  Plasticity = ability to change and adapt physically and functionally due to learning and experience. The younger we are the more plastic. As we age synaptic pruning takes place. This process keeps frequently used connections but rarely used connections are deleted. New connections can be made and these neural connections can change at any time - brain plasticity.
• Functional Recovery of the brain after trauma - transfers functions from a damaged area of the brain after trauma to other undamaged areas = neural plasticity.

  • Lashley's Equipotentiality Theory (1950)

  Rats were trained to run through a maze. An area of the brain was destroyed and rats were tested again but they found that one area was not associated with memory. Basic sensory and motor functions are localised but not higher order mental functions. Intact areas of the cortex could take over for specific cognitive functions.

  • Although you can't extrapolate from animals.
• Neuroscientists suggest the process can occur quickly after trauma = spontaneous recovery and then slow down after week or months. These individuals may require rehabilitative therapy.

  Neural unmasking = brain is able to to rewire and reorganise by itself by forming new synaptic connections close to the area of damage or dormant synapses are 'unmasked' to enable functioning to continue.

  Axon spouting = if axons are damaged the connections with the neuron will be too. Other axons in contact with the neuron will grow new nerve endings and connect with undamaged areas.
• Recruitment of homologous areas = opposite hemisphere takes over to perform specific tasks e.g. Broca's area damaged on the left, right side equivalent will take over and carry out it's functions.
• AO3 - Plasticity and Functional Recovery -

  • Localisation of function (contradictory theory)
  • Lashley (1950) Equipotentiality Theory (strength) higher order mental functions aren't localised and the rats could run the maze. (Functional Recovery)
  • Maguire et al found that the posterior hippocampus of London taxi drivers' brains was greater than the control (male non-taxi drivers). The longer they had been a taxi driver the more pronounced the structural differences were. (Plasticity)

  fMRI scans used, empirical methodology

  beta bias as only men were used as part of the sample
• AO3 - Plasticity and Functional Recovery -

  • Tajiri et al (2013) found that stem cells provided to rats after brain trauma showed a clear development of neuron-like cells in an area of injury. Demonstrates the ability of the brain to create new connections using neurons manufactured by stem cells.

  cannot extrapolate findings

  • RLA - neurorehabilitation, understanding led to uses of motor therapy and electrical stimulation of the brain to counter negative motor and cognitive functions following incidents. Helps improve cognitive functioning.
• Hemispheric Lateralisation (Split Brain)

  2 hemispheres of the brain are responsible for different functions.

  Left hemisphere is responsible for language.

  Right hemisphere is responsible for visual and motor skills.

  Corpus Callosum = nerve fibres that facilitate interhemispheric communication.

  Split-brain patient = someone who has had a commissurotomy operation so their corpus callosum has been cut in half. This means no interhemispheric communication they are now 2 separate streams of consciousness.
• Split-brain research: Sperry + Gazzaniga (1967) -

  Study involved case studies & experiments. 11pps had undergone split-brain surgery as a result of epilepsy. A control group not undergone commissurotomy. An image or word was presented to the patients left visual field (processed by right hemisphere) or vice versa. When info is presented to 1 side it couldn't be transferred to the other hemisphere due to a lack of interhemispheric communication. Given tasks to do -

  1. visual task
  2. drawing task
  3. auditory task

  The tasks they were given were only processed via the side given.
• AO3 Split-brain

  • Rare sample as commissurotomies are rarely carried out, procedure is also outdated, research lacks temporal & population validity as it can't be generalised to todays population.
  • Quasi, highly controlled follows standardised procedures which can be replicated, high reliability.
  • Research evidence - Sperry
  • Some pps still had a little interhemispheric communication, greater in some than others which reduces internal validity. Discredits the key principle of 2 separate streams on consciousness after commissurotomies.
• • Localisation of functions in the brain such as the somatosensory cortex, motor cortex, primary visual cortex, primary auditory cortex, Broca’s area and Wernicke’s area and research supporting these functional divisions.
  • hemispheric lateralisation refers to the notion that certain functions are principally governed by one side of the brain
• AO3 LOF -

  • functions such as language are too complex to be assigned to just one area and instead involve networks of brain regions (Bio reductionism)
  • equipotentiality theory – Lashley 1930 ~ issues with generalising from non-human animals to humans in lesion studies
  • issues generalising from case studies or from ‘abnormal’ patients, e.g. pps in the split brain research
  • discussion of patient J.W. who could speak about information presented to the left or right brain (Turk et al, 2002)
  • issues with generalising from studies with small participant numbers.
• Outline split-brain research -

  • 11 ‘split-brain’ patients have had their corpus callosum severed -no interhemispheric communication as a result of a commisurotomy
  • 2 separate streams of consciousness as there was no interhemispheric communication
  • Patients given visual & tactile tasks such as describe what you see in LVF that image would be processed by the right due to contra-lateral control whereas RVF would be processed by the left. Left - language dominant. Right - visual + motor skills
• AO3


  Split-brain research
• Turk et al (2002) study


  • Studied J.W. who had damage to their left hemisphere so couldn't speak
  • J.W. eventually learned how to speak with their right side equivalent
  • Contradicts the conclusions made about the right being only used for visual + motor skills
• Limitations of the study

  • Lacks replicability due to the nature of the sample as commisurotomies are rarely carried out
  • Rare sample with epilepsy so lacks population validity
  • The degrees of interhemispheric communication varied (some had their corpus callosum severed to a smaller degree = confounding variable)
  • Some patients had experienced drug therapy for much longer than others
• Outline the difference in function between Broca’s area and Wernicke’s area.

  • Broca’s area is responsible for speech production whereas Wernicke’s area is responsible for language comprehension
  • Broca’s area enables speech to be fluent whereas Wernicke’s area enables speech to be meaningful
• Localisation of function in the brain -

  • concept of functional localisation
  • concepts of hemispheric lateralisation and contralateral organisation
  • localisation of the motor, somatosensory, visual, auditory and language centres
  • outline of functions assigned to motor, somatosensory, visual, auditory and language centres
• AO3 -

  • research evidence to support localisation of function, e.g Phineas Gage + Tan
  • challenges to localisation of function equipotentiality theory – Lashley’s work with rats, discussion of individual differences
  • issue of reductionism
  • methodological critique of evidence – issues of generalisation from animal research