Functional Lateralization Flashcards
What is laterality?
there are two cerebral hemispheres with separate functions
Laterality is…
relative, not absolute
Hemispheres play a role in…
all behaviours but one is more dominant
What affects laterality?
Environmental and genetic factors
In 1860 who made the first observations?
Hughlings-Jackson and Pierre Gratiolet
What were Hughlings-Jackson’s and Gratiolet’s findings?
cortical convultions on the LH mature more rapidly than those on the RH
Observations were largely ignored until…
1960’s when Geschwind and Levitsky renewed interest
How many anatomical differences have been confirmed?
8
The first anatomical differences is…
RH slightly larger/heavier, LH has more grey matter
The second anatomical difference is…
marked structural asymmetry between temporal lobes
The third anatomical difference is…
asymmetry in the cortex of temporal lobes correlates to midbrain asymmetry in the thalamus
the fourth anatomical difference is…
slope of lateral fissure gentler in LH
the fifth anatomical difference is…
Frontal Operculum organised differently in LH
The sixth anatomical difference is…
distribution of various neurotransmitters asymmetrical both in cortical and subcortical regions
The seventh anatomical difference is…
RH extends farther anteriorly, LH extends farther posteriorly. Five times more likely that the occipital horns of the lateral ventricles are longer on the RH
The eighth anatomical difference is…
details of anatomical asymmetry affected both by sex and handedness
Cerebral asymmetry was first established how?
studying patients with neurological disease lateralised to one hemisphere e.g. epilepsy
How do we conclude a cortical area is specialised?
Demonstrate lesions in other areas don’t produce a similar deficit.
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 the other
Examples of double dissociation are…
LH lesions result in deficits in language functions
RH lesions result in deficits in spatial tasks
What is Jun Wada credited with?
Injecting sodium amobarbital into the carotid artery creating anaesthesia of the ipsilateral hemisphere - the Wada test
When is the Wada test typically used?
before surgery in epileptic patients to establish language dominant hemisphere
Brenda Milner demonstrated…
98% right handers are LH language dominant
70% of left handers are LH language dominant
2% of right handers are RH language dominant
15% of left handers are RH language dominant
15% of left handers are bilateral language dominant
What are commissurotomy studies?
Split brain studies
In the 1940s a common procedure to treat epileptic seizures was…
cutting the Corpus Callosum or the Anterior Commissure - with no severe deficits
In the 1950s who severed the Corpus Callosum of cats and monkeys?
Sperry
What did Sperry do in the 1950s?
Using visual discrimination found that information never crossed to the other hemisphere.
What’s the role of the Corpus Callosum?
allows cortical areas from one hemisphere to communicate with cortical areas of the other hemisphere
In the 1960s what technique did Vogel and Bogen use?
tachistoscopic presentation
What have language studies shown?
Flashing a word to the RVF split-brain patients can say it, but not when it is flashed to the LVF, but can collect the right object using the left hand
What can be concluded from language studies?
LH is responsible for language, RH has reasonable comprehension ability
What are spatial organisation studies?
Flash a 3D drawing to the RVF (in split-brain patients) and right hand cannot replicate the drawing, but flashed to the LVF, right hand can.
What can we conclude from spatial organisation studies?
RH is responsible for spatial organisation
What are perception studies?
illusory contours reveal that human RH can process some things the LH cannot
What do synthesis studies show?
there is no synthesis across hemispheres, but each hemisphere is capable of synthesis
What has techistoscopic presentation shown in the intact brain?
LH/RVF has an advantage for words
RH/LVF has an advantage for faces and other visuospatial stimuli
Using dichotic listening in the auditory system we have found…
LH has an advantage for words and linguistic decisions
RH has an advantage for melodies
there’s no ear advantage for vowels
What are the two types of theories?
Specialisation theories and interaction theories
What do specialisation models say?
only one hemisphere facilitates a given psychological process
LH = more logical
RH = primarily a synthesizer
What do interaction models say?
both hemispheres have the capacity to perform all functions but do not
According to interaction models, what versions exist>
1 - hemispheres function simultaneously but work on different aspects of processing
2- they inhibit or suppress each other’s activity
3- they receive information preferentially and perform analyses simultaneously
