Lateralisation , Language & Split Brain Flashcards
Aphasia
Deficit in language comprehension or production due to brain damage
Broca
Reported results of post mortem examination of two aphasic patients
-patients with deficits in Lang (not able) general sensory motor or intellectual dysfunction
Both had left hemisphere damage centred in left pre frontal
Lobe
Known as broas area
Apraxia
Difficulty performing movement s with either side of the body when asked to do so
Liepmann discovered associated with left hemisphere damage
Right hemisphere became dominant
More activity in left than right during language
Test of cerebral Laterlisation
95% of right handed participants are left hemisphere dominant for speech
70% of left are also left hemisphere dominant
However damage can cause right to become dominant
Split brain experiment Background
In 1953 Myers and speedy performed experiment on cats
Provided means of comparing the function of two hemispheres
To reveal the function of the corpus callosum- transfers learned info from one hemisphere too other, when cut functions independently
Split brain experiment 4 cats
Corpus callosum severed
Optic chain severed
Corpus and optic severed
Intact controls
Split brain (experiment)
Phase 1 cats learned a lever press pattern discrimination task with a patch over an eye
Phase 2 switched to other eye
Groups 1,2 and 4 performance kept same
In contrast group 3 , the optic chiasm and callosum severed group acted as if the task were completely new to them
Split brain experiment (conclusion)
Has capacity as two separate fore brains , each capable of independent learning and of storing its own memories
Function of corpus callosum is to carry info between hemispheres
Best way to study is to use a method to limit info to one hemisphere
Tests of split brain patients
First serve corpus callosum was 1940 due to epilepsy to help to reduce severity
Is effective and appeased to have few obvious effects
-visual stimuli are flashed to the right or left of fixation point
Also tactual info is presented to one hand under a ledge
Two independent streams of consciousness (L Hemi)
Object presented to the left hemisphere either by touching with right hand
-viewing something in RVF
The patient able to:
-pick out the correct object with right hand
-but could not pick out th correct object with left hand
-could name correct object
Two independent streams of consciousness (R Hemi)
Object presented to right hemisphere -touching something with left hand -Viewing something in left visual field The patients could: -could pick out the correct object with left hand -not not pick correct with right l Claimed nothing was presented
Cross Cuing
Communication between hemisphere by nonneural route
50% guessing chance (red or green light flashes in LVF)
Guy did perfect - Conclusion
The right hemisphere heard incorrect guess from left and signalled it was wrong by shaking head
Learning two things at once
Split brains capable
If split is visually presented two objects at same time , he can reach into two bags and pick the correct item
Helping Hand Phenomenon
Occurs when to two hemispheres are presented with different info about correct choice, then asked to reach out and pick object
Usually right hand will chose what left hemisphere saw , but what right sees is an error and makes left hand grab right and pull it over to other object
Differences in left and right hemispheres
Language is the most lateralised of all abilities;the left hemi is better than the right at most language related tasks
- right hemisphere is able to understand single written and spoken words
- right Hemi better at task involving spatial ability, emotional stimuli and music tasks
Hemispheres engage in different types of memory processing
LH attempts to place it’s experience in larger context
RH attends strictly to the gestalt perceptual characteristics of the stimulus
This is usually termed analytical (LH) versus holistic (RH)
This RH should not be regarded as minor
Three theories of Cerebral Asymmetry
Analytic synthetic theory
Motor theory
Linguistic theory
Analytic-Synthetic theory
Suggest that there are two fundamentally different modes of thinking , an analytic mode (LH) and synthetic mode (RH)
Neural circuitry is fundamentally different for each
-LH operates in logical, sequential, analytic fashion
RH makes immediate, overall synthetic judgements
Motor theory
Suggest LH is specialised for fine motor movement of which speech is but one example - Evidence :
Lesions of the LH disrupt facial movements more than do RH lesions even when they are not related to speech
-Degree of disruption of non verbal facial movements is positively correlated with the degree of aphasia
Linguistic Theory
Primary function of LH is language; based on studies of deaf people who communicate using SL this ability is lost if people suffer damage to LH , even if the are able
To make movements required
Broca’s Area
Inferior left prefrontal love in left hemisphere
Damage leads to deficits primarily speech production but also comprehension
Characterised by inability to initiate well articulated conversational speech
Common cause stroke
Wernickes Area
Left temporal lobe , just posterior to the primary auditory cortex in the superior temporal gyrus
Damage leads to semantic language comprehension
Also speech is incomprehensible , despite having correct grammar , rhythm and intonation
Recovery is possible after stroke
Other disorders of speech production
Transcortical sensory aphasia - repeating words other people say
Transcode rival motor aphasia - individual can’t produce spontaneous speech
Apraxia speech , known as dyspraxia
Verbal auditory Agnosia- pure word deafness, inability to comprehend
Conduction aphasia- comprehension and spontaneous speech are intact but patient not able to repeat words they have just heard
