Functional lateralisation

what is lateralisation?
two hemispheres have distinct functions - but doesnt mean that one hemisphere does everything, but one is dominant (relative)
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what is cerebral site?
where in the brain/hemisphere
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what is cerebral side?
what side of the brain
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what is laterality affected by?
environmental and genetic factors - e.g. left-handers and women appear to have more integrated cerebral organisation - differences in functionality
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what did Hughlings-Jackson and Gratiolet do in 1960's?
first observed that the cortical convolutions on the left-hemisphere (LH) mature more rapidly than those on the right
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how are babies brains when they are born?
almost with a flat surface - isnt fully developed, but develops and generates more neurons as we go through childhood/adolescence and then stops maturing
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how many major anatomical differences are there between the 2 cerebral hemispheres?
8 - they reflect the functional asymmetries
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what is the first asymmetry?
RH is slightly larger and heavier, but LH has more grey matter
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what is the second asymmetry?
marked structural asymmetry between the temporal lobes
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what is the third asymmetry?
midbrain asymmetry in thalamus - correlated with the asymmetry in cortex of temporal lobes
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what is the fourth asymmetry?
slope of lateral fissure gentler in LH - temporoparietal cortex lying ventral to lateral fissure is larger on RH (bigger)
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what is the fifth asymmetry?
frontal operculum is organised differently/more varied in LH and RH - visible area is 1/3 larger on RH, area buried in sulci is larger in LH
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what is the sixth asymmetry?
RH extends further anteriorly, LH extends further posteriorly
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what is the seventh asymmetry?
distribution of various neurotransmitters is asymmetrical in cortical and subcortical regions
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what is the eighth asymmetry?
details of anatomical asymmetry affected both by sex and handedness
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?what type of asymmetries do we have?
structural and functional
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where did the first indication of asymmetry come from?
neurological patients that have diseases affecting a hemisphere (e.g. epilepsy) and concluded that if a cortical area has a special/lateralised function, we need to show that lesions in other areas dont produce the same deficit
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what is double dissociation?
two areas of the neocortex are functionally dissociated by two behavioural tests - each test being affected by a lesion in one area but not another - e.g. LH lesions = deficit in language functions, RH = deficit in spatial tasks
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what is the Wada test? (carotid sodium amobarbital (SA) injection)
pioneered the technique of injecting SA into carotid artery to produce a brief period of anaesthesia of the ipsilateral hemisphere - typically used in epileptics before surgery to establish language dominant hemisphere
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outline the process of the SA injection
left carotid injected --> LH anaesthetised --> patient cant speak or move right arm (RVF)
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what did Brenda Milner demonstrate?
98% right handers and 70% left handers have LH language dominance - 2% right-hand and 15% left-hand have RH language dominance --> 15% left-hand have bilateral language dominance
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why are split brain studies used?
to understand what each hemisphere is dominant at
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what is split-brain?
corpus callosum cut/severed - introduced in 1940's - suffered intractable epileptic seizures and low quality of life, but once split-brain they had no severe deficits so didnt know what its function was
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what did Sperry do in the 1950's? (split brain)
experiments with cats and monkeys to study split brain - severed corpus callosum, anterior commissure, and optic chiasm - taught animals visual discrimination and tested with one eye closed - found info never crossed to the other hemisphere
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what did Sperry conclude from experiments?
corpus callosum allows cortical areas to communicate and transfer info between the two hemispheres
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what did Vogel and Bogen do in the 1960's? (split brain)
same surgery with epileptic patients - due to anatomy of the visual system, stimuli presented in right visual field reflects LH processing (+ vice versa)
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example of language studies on split brain patients?
flash word BANANA to RVF/LH - split brain can say word but if flash to LVF/RH unable to say word - but can if able to choose object with left hand -- can do language comprehension not production
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example of spatial organisation studies on split brain patients?
flash 3D line drawing to RVF/LH and ask right-handed pps with right hand they cant do it - if you flash cube to LVF/RH and ask same pps to do it with left hand they can -- spatial organisation must be done by RH
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example of perception studies?
illusionary contours reveal the RH can process some things LH cant - LH cant see the difference in illusions, but RH can
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example of synthesis studies?
how much lang each H can do and whether we can synthesis across - shown words that when put together create an object (e.g. bow and arrow) and compound words - if the words went together they could synthesise, but couldnt for compound
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what conclusions are drawn from synthesis studies?
split brain patients cant synthesise across hemispheres (because LH is about language) - but can synthesis within a hemisphere (RH)
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behavioural asymmetry using tachistoscopic presentation?
LH advantages for words, RH advantage for faces/visuospatial
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behavioural asymmetry using dichotic listening?
LH advantage for words/digits/morse code/difficult rhythm/tone used in linguistic decisions (dominant for language) -- RH advantage for melodies/musical chords/environmental sounds/tone independent of linguistics
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what is there no ear advantage for in dichotic listening tasks?
vowels, rhythms, and non-melodic hums
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what two groups do lateralisation theories fall into?
specialisation theories (propose unique functions for each hemisphere) and interaction theories (cooperation between the hemispheres - so less competition)
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what do the specialisation models suggest?
1 hemisphere facilitates a specific process - LH operates in logical/analytic fashion, analyses input sequentially, verbal labels, & abstract relevant details - RH primarily synthesiser, overall stimulus configuration, organising/processing whole
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what do the interaction models suggest?
both hemispheres capacity to perform all functions but dont
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what are the 3 versions as to why hemispheres dont perform all functions all the time?
1. hemispheres function simultaneously but work on diff aspects (complimentary processing) - 2. they may inhibit/compete with each others activity - 3. both receive info preferentially but these analyses are different
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evaluation of theories?
little evidence - provide behavioural complement to anatomical study of neurological patients - individual differences? - little disagreement about asymmetry - but considerable disagreement about why the 2 hemispheres are asymmetrical
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what did Gazzaniga (1967) say about the brain?
the human brain is actually two brains -when cerebellum divided surgically its as if the cranium contained 2 separate spheres of consciousness
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where do false memories originate?
in the Left hemisphere - fMRI image: false = yellow, true = red
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what is symmetrical in the brain?
many functions of the cerebral hemisphere
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Card 2


what is cerebral site?


where in the brain/hemisphere

Card 3


what is cerebral side?


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Card 4


what is laterality affected by?


Preview of the front of card 4

Card 5


what did Hughlings-Jackson and Gratiolet do in 1960's?


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