3 - Brain Localisation + Lateralisation Flashcards
What is localisation?
The theory that different areas of the brain are responsible for specific behaviours, processes or activities
What is another term for brain localisation?
Cortical specialisation
What was the belief about brain function before the localisation theory?
Holistic theory (all parts of the brain work together to cause processes/behaviours)
What will damage to a certain area of the brain cause?
The loss/impairment of the certain function associated with that area
What are the three concentric layers that make up the brain?
- The central core
- The limbic system
- The cerebrum
Which concentric layer do we look at predominantly regarding brain localisation + lateralisation?
The cerebrum
Outline the features + function of the central core
Features…
- Bottom layer of brain
- Includes: brain stem, cerebellum, hypothalamus
Functions…
- Regulates primitive functions (eating, sleeping, etc)
- Helps with homeostasis (maintaining constant bodily state)
Outline the features + functions of the limbic system
Features…
- Middle layer of brain
- Includes: connection to hypothalamus, hippocampus
Functions…
- Regulates emotions
Outline the features + functions of the cerebrum
Features:
- Made of left + right hemispheres
- Hemispheres connected by corpus callosum
Functions:
- Regulating higher intellectual processing
- Lateralisation suggests left + right side have differently functions
What is lateralisation?
Theory that the two hemispheres of the brain (of the cerebrum) are functionally different + responsible for different mental processes + behaviours
What is the right hemisphere’s function?
- Controls left side of body
- The ‘synthesiser’ (holistic)
- Specifically important for: emotion, holistic thought, creativity, face recognition
What is the left hemisphere’s function?
- Controls right side of body
- The ‘analyser’ (breaks down + analyses)
- Specifically important for: language, analytical thought, logic + sequencing
What is the corpus callosum
The bundle of fibres that connects the two cerebral hemispheres
- Enables communication between hemispheres
How many lobes is each hemisphere divided into?
4
What are the names of the hemispheres’ lobes + their basic function?
- Frontal lobe (movement, thinking, emotions)
- Parietal lobe (senses, attention)
- Temporal lobe (hearing)
- Occipital lobe (vision)
What are the lobes of the cerebral hemisphere covered in?
Cerebral cortex (grey, 3mm thick, divided into multiple cortices)
What are the cerebral cortex’s cortices?
- Motor cortex
- Somatosensory cortex
- Auditory cortex
- Visual cortex
Motor cortex - location? Function? Effect of damage?
Location: back of frontal lobes
Function: conscious movement (control opposite sides of body)
Effect of damage: loss of control over fine movements
Somatosensory cortex - location? Function? Effect of damage?
Location: front of parietal lobes
Function: representation of sensory info, e.g. feeling pain, heat, etc
Effect of damage: issues processing sensory info
Auditory cortex - location? Function? Effect of damage?
Location: temporal lobe (by ears)
Function: receiving + processing auditory info (hearing)
Effect of damage: loss of hearing
Visual cortex - location? Function? Effect of damage?
Location: back of occipital lobes
Function: sending visual info from visual field to opposite visual cortex (sight)
Effect of damage: loss of vision (blindness)
Which side of the brain is language lateralised to?
Left
What are the two language centres of the brain?
- Broca’s area
- Wernicke’s area
Broca’s area - location? Function? Effect of damage? Discovered by?
Location: left frontal lobe
Function: language production (speech)
Effect of damage: Broca’s aphasia - cannot produce speech properly (slow + broken)
Discovered by: Looking at Patient Tan (could understand language heard but could only say one syllable: ‘Tan’)
Wernicke’s area - location? Function? Effect of damage? Discovered by?
Location: left temporal lobe
Function: language comprehension (understanding)
Effect of damage: Wernicke’s aphasia - can only produce neologisms (nonsense speech) that isn’t understandable
Discovered by: Looking at patients with damaged left temporal lobes
Give 2 positive evaluation points for localisation of brain function
Evidence from brain scans
- Brain scans show brain activity in certain areas when completing certain tasks
- E.g. Peterson et al used scans to show Broca’s area activity during a reading task + Wernicke’s area activity during a listening task - supporting localisation of language to these two areas
- So, scans have produced objective, reliable, scientific evidence for localisation, allowing the formulation of general laws
- BUT - involves inferences (that activity means controlling behaviour)
Success of neurosurgery
- By treating an area where a mental disorder has said to be localised, the mental disorders have reduced
- E.g. Cingulotomy - OCD said to be localised in the cingulate gyrus region + by isolating it in 44 OCD patients Doughtery found 30% success in treating their OCD
- Success in treating certain mental disorders by focusing on certain areas supports theory that function is localised
Give 2 negative evaluation points for localisation of brain function
Gender bias in localisation research
- Localisation has been criticised for beta bias, as research was only on men + assumed womens’ brains the same
- Since, research has shown women have a larger Broca’s area + superior language skills
- So, localisation theory is based on androcentric research + may not be generalisable to everybody (ie. Women)
Alt. theories of equipotentiality + plasticity
- Equipotentiality = basic motor + sensory functions are localised, but higher cognitive functions are spread across the brain
- Supported by Lashley - removed 10-15% of rats’ brains + found their ability to learn a route round a maze wasn’t affected by the removal of certain areas, but by the total amount removed
- Plasticity = after brain damage, functions can be relocated to non-damaged areas
- Supported by stroke victims
- So, there is support for the idea that some localisation exists, but it isn’t such a set theory and the brain is able to adapt
What does contralateral refer to?
The idea that the hemispheres of the brain are ‘cross-wired’ (control the opposite sides of the body)
Are all functions lateralised?
No
- E.g. sensory representation (somatosensory cortex in both hemispheres)
What is split brain research?
A series of studies which began in the 1960s and are ongoing, involving people with epilepsy who had experienced treatment involving the surgical separation of their cerebral hemisphere
What does split brain surgery do?
Severs the corpus callosum
What are the effects of split brain surgery?
- Stops large epileptic seizures (severs the connection between the hemispheres so an ‘electrical storm’ cant flow between and cause a seizure)
- Stops the two hemispheres being able to communicate
Who was the most important psychologist who did split brain research?
Sperry (1968)
What was Sperry’s aim?
To test hemispheric lateralisation (extent to which behaviours are controlled by one side of the brain)
What was Sperry’s sample?
- 11 ppts (10 men + 1 woman)
- All had split brains after previous epilepsy problems
How was Sperry’s split brain research controlled?
- In a lab
- Any images used only shown for less than 1/10 sec so eyes cant move + one hemisphere is definitely tested at a time
- Used a control group to compare experimental groups’ performance with (11 people with no epilepsy + ‘normal’ connected brains)
Outline Test 1 completed by Sperry + the findings
1) Describe what you see
- Images shown to right visual field for <1/10 sec
- Processed by left hemisphere
- Could describe it with words (language in left)
- Images shown to left visual field for <1/10 sec
- Processed by right hemisphere
- Couldn’t describe it with words or said they didn’t see it
- Could draw it (so did actually see it but can’t use language)
Findings: Language lateralised to left hemisphere
Outline Test 2 completed by Sperry + the findings
2) Recognition by touch
- Object placed in right hand
- Processed by left hemisphere
- Could describe it with words (language in left)
- Could select it from a grab bag
- Object placed in left hand
- Processed by right hemisphere
- Couldn’t describe it with words
- Could select it from a grab bag
Findings:
- Language lateralised to left hemisphere
- Some capabilities aren’t lateralised (somatosensory)
Give 2 evaluation points for hemispheric lateralisation
NEG: Plasticity
- Neural plasticity suggests functions aren’t so fixed (challenges hemispheric lateralisation)
- Research on patients with damage to one hemisphere has shown functions can be taken over by the other healthy hemisphere
- E.g. speckles of language in right hem of left stroke patients
- So, brains may be able to adapt to damage, meaning lateralisation is more fluid than was thought
NEG: Pop psychology
- Pop psychology has over simplified the theory of lateralisation
- E.g. quizzes about what ‘sided brain’ you have
- Although left side is more analytical + right more holistic, they are both important + normally in constant communication
- So, pop psychology skews the validity of the the theory that is available to the public
Give 2 evaluation points for Sperry’s split brain research
POS: Some forms of control
- Standardised + controlled his procedures
- E.g. lab, images shown for <1/10 sec, control group
- Increased internal validity (testing hemispheres we want to test) + reliability (easily repeated)
- Control allows for repetition + formulation of general laws
NEG: Methodological flaws
- Despite control, some flaws did lower the internal + external validity
- E.g. lowering internal - control group didn’t have epilepsy too (hard to establish cause-effect with multiple differences between groups)
- E.g. lowering external - small sample (11) so may not represent whole population
- These issues lower the validity of the laws formulated
Define plasticity
The brain’s ability to change and adapt as a result of experience + new learning. This involves the growth of new neural connections.
When is the brain most ‘plastic’?
During infancy
- Rapid brain development, making lots of synaptic connections
- Number of synaptic connections peaks at age 2-3 yrs
What was originally believed about neural plasticity in adulthood?
Brain fixed by then - no plasticity
What is now believed about neural plasticity in adulthood?
Brain continues to change
Cognitive pruning - existing connections deleted + strengthened depending on use
Some new connections made - due to new learning + experiences
What are pros of having neural plasticity?
- Ability to learn new things
- Ability to enhance existing cognitive capabilities
- Ability to maintain functionality after damage (functional recovery)
What is a con of having neural plasticity?
- Changes in brain can be bad (e.g. prolonged drug use weakens connections via cognitive pruning, causing poorer cognitive functioning)
What research supports plasticity?
Maguire - London Taxi Drivers
Outline the research + findings completed to support plasticity
Maguire - London Taxi Drivers
Research:
- Used MRIs to compare volume of grey matter in the posterior hippocampus of London taxi drivers to a matched pairs control group.
Findings:
- Taxi driver group had on average much higher vol of grey matter in their posterior hippocampus than control group
- The longer their time as a taxi driver, the larger the hippocampus
Conclusions:
- Taxi drivers’ hippocampi enlargen (plasticity) to adapt to their training (for ‘the knowledge’ of streets + routes)
What is the posterior hippocampus associated with?
Development of spatial + navigational skills
Give 3 evaluation points for Maguire’s research on plasticity
GOOD - Real world example, high external validity
GOOD - Controlled, objective design increased internal validity (matched control group - reduced individual differences) (used MRI - objective and replicable)
BAD - Can’t confirm cause + effect, didn’t measure hippocampus before, people born with a larger hippocampus may be more likely to be taxi drivers
Give a positive evaluation point for plasticity
Helpful throughout life
- Greatest during infancy but doesn’t stop completely
- Benefits of adapting + changing our brains are gained throughout life
- E.g. Bezzola - used fMRIs to measure increased motor cortex activity in an experimental group (aged 40-60) who did 40hrs golf training, compared to control group who didn’t
- Research supports the helpful role of plasticity throughout life
Give a negative evaluation point for plasticity
Brain can change in a negative way
- The bran can adapt + change for the worse
- E.g. Medina et al find brain’s adaption to drug use caused loss of connections, poorer cognitive functioning, higher dementia risk
- E.g. Phantom limb syndrome - 60-80% of amputees feel pain in lost limb due to remapping of connections in somatosensory cortex
- Brain’s ability to change + adapt isn’t always positive
Define functional recovery
A form of plasticity that occurs after brain damage.
The brain adapts + redistributed functions to undamaged areas.
What is the difference between plasticity + functional recovery?
Plasticity - general ability of brain to change + adapt
Functional recovery - specific change AFTER DAMAGE
When does functional recovery occur most quickly?
Straight after trauma, then slows
When should individuals with brain damage seek rehabilitative therapy?
Straight away - recovery is easier then, with more spontaneous recovering happening naturally at this time
What happens in functional recovery?
Brain forms new synaptic connections
- ‘Unmasks’ secondary, dormant neural pathways in non-damaged areas capable of completing the damaged function
Brain undergoes structural changes
- Axon sprouting
- Reformation of blood vessels
- Recruitment of homologous (similar) areas in opposite hemisphere
What is axon sprouting?
When new nerve endings grow and connect with undamaged areas to form new pathways
Give a positive evaluation point for functional recovery
Real-world application
- Understanding processes involved in functional recovery has helped improve neurorehabilitation
- E.g. understanding axonal growth has helped with new treatments such as constrained-induced movement therapy (stroke patients encouraged to move affected part + keep other areas still to promote axon sprouting)
- Also known to start rehabilitation strait away (brain most plastic)
- So, research into functional recovery has helped medical professionals improve treatment in the real world
What is a piece of research that supports plasticity, not done on humans?
Lashley’s Rats
- Removed 10-50% brains
- Could still navigate maze because undamaged areas compensated
Give a negative evaluation point for functional recovery
Cognitive reserve
- Cognitive reserve suggests that the ability of functional recovery is limited by level of education
- Suggests some uneducated people are less able to recover from brain damage
- E.g Schneider - 16+yrs education: 40% had disability-free recovery
- <12 yrs education: 10% had disability-free recovery - Suggests education level (linked to socio-economic status) limits success of functional recovery (socially sensitive)
