Lecture 14/15/16: Corpus Callosum and Apraxia Flashcards
What is the corspus callosum and what is its function?
Large white matter bundle (a lot of axons that start from 1 hemisphere and go to the other hemisphere), over 200 millions axons. Bilateral connectivity!
Function:
→ Transfer and integration of information between the two hemispheres.
→ between homologous brain regions.
→ Interhemispheric communication (send information from one hemisphere to another)
Other commisural fibres
Corpus callosum (biggest one)
Anterior commissure
Posterior commissure
Hippocampus commissure
These 3 are not as useful for interhemispheric communication.
What are the different techniques you can use to see the corpus callosum?
- Structural MRI
- Diffusion MRI: Corpus callosum is uniformly red in diffusion imaging (CC is white matter tract)
The CC is almost the only thing attaching the two hemispheres.
What are the different ways to study the corpus callosum?
The corpus callosum can be divided into subsections and each subsection connects specific homologous areas of the brain. This parcellation is usually referred to as the Witelson Parcellation (7 regions).
In order to study the different sections and what their role is, they parcellated the CC into the 7 sections. Mathematical separation, not based on function or cytoarchitecture.
How did they go about the division of the corpus callosum?
Parcellation
- This parcellation and association between each part of the CC and what brain areas they connect comes from experimental work with monkeys (ablation/sectioning and tracing).
- And clinical work with humans (study patients with lesions in the CC and see where their deficits are)
- These callosal regions may be associated roughly with various cortical regions, although there is considerable overlap” Witelson
- Separated in half and then first third, last third, first fifth and last fifth. Gradual passing from one section to the next.
Diffusion imaging
Put a seed or region of interest in one section of the corpus skeleton, you can see with diffusion imaging where those fibres go roughly.
What is the function of each part of the corpus callosum, what parts of the brain do they connect??
Genu: connects the very anterior part of the frontal lobe and orbitofrontal areas
Rostral body: Connects premotor areas and also go on top of the supplementary motor areas.
Anterior mid body: connects sensori-motor areas (around the central sulcus)
Posterior midbody: connects the more anterior parietal areas
Isthmus: connects posterior parietal areas
Splenium: connects the occipital areas of the brain and they go to some parts of the anterior temporal lobe.
Parcellated the CC into 25 equal sections to be able to see how gradual connectivity was. It is not complete one to one mapping with the Witelson Parcellated area and the region they connect.
How do the results from the tracing in monkeys compare to the results with the diffusion imaging in humans?
Study that related diffusion imaging in human results with the little table from tracing studies in the monkeys and the correspondence is very similar. The diffusion imaging studies support what is found with the monkey tracing research.
What is the microstructure in the CC??
-Microstructural organization of axons vary along the CC (axon properties will vary from one area to another).
Things that can vary: circumference of the axon (size), myelination and density of the axons in one space) . These will all affect the transmission of the information from one region to another.
Bigger axons, more myelinated or just more axons will make the transfer faster between one area to another. Measure the speed of info transfer between the 2 hemispheres.
- Properties such as fiber density and axon diameter affect the conduction of information.
- It is possible to measure the speed of information transfer by the CC.
Visual field and CC
If you present something quickly in the left visual field, it will I only be perceive by the right visual cortex. If your corpus callosum is intact, the information will be transferred right away.
MEG/ EEG very goof for temporal resolution. Could see that the right hemisphere receives the info a little bit before the left hemisphere.
FMRI: Temporal imaging is not so good. You cannot se the CC.
The crossing that happens from the motor cortex to the hand. If you want to use the left hand, the right motor cortex controls the left hand.
Poffenberger Paradigm
1912
- Measures InterHemispheric transfer time (IHTT)
Used light projection and varied whether it was flashed in the right or left visual field and also varied the instruction to the participants (use right hand, use left hand). Experiment to understand the crossing between the motor and visual areas of the CC to measure the interhemispheric transfer time. Light flashes very fast to make sure that it is perceived first by one visual hemifield. Participant click a button every time they see a square
Question: Where does the transfer occur in the corpus callosum?
at the visual level (dotted line)
at the motor level (full line)
To answer:
1) Manipulate motor and visual aspects in turn and see which affects the transfer time (placed it further or closer in the visual fied, darker or lighter).
2) Localised CC lesions –> the fastest way for neuronal transfeer of infor was from occipital to motor and then between the homologous motor areas.
Answer –> transfer is faster at the motor level.
Crossed trials are slower!! by a few milliseconds
if i use right hand and the light is in the right visual fied –> info can stay in one hemisphere to produce a task. Flashed in right visual field, left occipital areas receive info, sent to left motor areas to control right hand.
If stimulus in left visual field –> right occipital areas receive info, right hand to click in response the info needs to cross to other hemisphere.
Left visual fied and need to press with left: no crossing necessary.
Why is the corpus callosum useful??
Two hemispheres working together
* Motor coordination - if you want to move at the same time or in a sequence.
* Language (LH is dominant)
- Pragmatic (use of language in social circumstances)
- Understand non-literal expressions, affective prosody (intenations)
* Emotion processing
- Facial expression
- Regulation/managing emotions
- Verbal expression
Corpus callosum differences and
abnormalities
1) Normal variations in the population
- Sex: some subregions of the CC are larger in women
- Manual preference: CC larger in left handed individuals
2) Acquired abnormalities
- Callosotomies (surgical sectioning of the callosoomy)
- Traumatic brain injuries
- Strokes…
3) Developmental abnormalities
- Corpus callosum agenesis (baby born without orwith part missing)
- Variations in developmental disorders: the example of autism
History of corpus callosum
- As early as in the 19th century, Wernicke, Dejerine and others were aware that interhemispheric communication was essential for high-order cerebral functions.
- Later, Split-brain experiments on animals and human patients with section of the CC (cats, monkeys)
- Geschwind, 1965: ‘Disconnection syndrome in animals and man’ based on lesion studies
- Sperry, Bogen and Gazzaniga, 1969: ‘Interhemispheric relationships. Syndromes of hemisphere disconnections
What is th split-brain?
The split brain is when you completely cut the corpus callosum. This allows you to study lateralization of function and what the patient is lacking when the two hemispheres are seperateed.
Roger Sperry (1959-1968)
* Studied the functional specialisation of each hemisphere
* Surgery to cut the corpus callosum in some epileptic patients
* First observation: no apparent cognitive damage! Almost normal
* But… when designing the right experiments, were able find specific deficits and learn about hemispheric specialisation.
Roger Sperry’s Split Brain Experiment
Mainly cats and monkeys
* The main discovery → when you cut the connections between the two brain hemispheres: each hemisphere functions independently as if each was a complete brain (as if the animal has two seperate brains).
* Train one side of the brain: the other side of the brain doesn’t know anything about it. The two hemispheres were working in isolation
* Divide the optic chiasm so the visual information is only presented to one hemisphere
Explain Myers and Sperry’s experiment
→If you cut the CC and the optic chiasm
* Only the information from one eye is transmitted to one hemisphere (right visual fied gives info to right hemisphere)
* Blindfold the other eye
* Can teach a task to one hemisphere only
* Then move the patch to the other eye: no memory or effect of the learning from the other eye (no memory of the task because the this brain hemisphere didnt see anything that was happening)
* Compared to control cats (blindfold technique): learning is transferred to the other hemisphere
Results:
either CC or optic chiasm is sectioned = patch on first eye, learn which to pick to get the result and read 100% success. Move patch to the other eye and still have 100% success
both CC and optic chiasm sectioned = had to relearn it when patch was transferred.
Explain Sperry’s human case example 1
Visual stimulation –> force the information to be seen by one hemisphere only.
In humans, they do not have a section of the CC.
* The patient fixed his gaze on a central point on a board
* Lights are flashed in both the left and right visual hemi field
- Ask the patient: what did you see?
- Answer: ‘’light flashing in the right hemi field’’
* Flash lights in only the left hemifield
- Ask what did you see: they deny having seen any lights. The left hemistphere has to verbalize the answer, there was nothing in the right visual field.
- If you ask them to point where the lights were flashed instead of asking for a verbal answer, they point to the correct side. The information cannot be transfered to the left speaking hemisphere, but the patient can use the right motor cortex to select what theys see.
* Speech is in the left hemisphere!
Sperry human case - Example 2
Tactile stimulation/discrimination test
* Object in the right hand :
- able to name and describe the object
- Object in the left hand:
- not able to name or describe
- able to match it to the same object in a collection of object presented visually.
- would be able to tell that they are holding something.
- Not crossing in the hemisphere
- only some somatosensory ipsilateral crude input
Ex: Presence/absence of stimulationThis proves that the right hemisphere does the perception, its just not able to do the language aspect of naming or describing. It can feel the object and choose a matching object in a collection of objects.
Explain Sperry’s human case example 3
- A picture or written information is flashed in one hemifield
OR - An object is placed out of view in one of the patient’s hand
1) If presented to the left hemisphere (right visual hemifield or right hand):
→ Able to name and describe (verbally and in writing)
2) If presented in left hand or left visual hemifield and asked to name it:
→ wrong guess
Even when they have the object in their hand, still unable to name it (knowledge remains in the right hemisphere)
But able to give a non-verbal answer (find the object with the left hand, identify the pencil by touch, or point)
Sperry and Gazzaniga experiment
In this experiment, they flashed two words or two pictures at the same time. So the patient sees both things at the same time. If they ask the patient to verbally answer what they saw:
* The left hemisphere can verbally say what is in the right visual field: ‘‘Apple’’
If they ask them to show you what they saw with the right hand they would point to the spoon:
Or show with the right hand (not the left hand). They can point at the spoon or chose the spoon.
This experiment showed that the 2 hemisphere worked independently at the same time and don’t have a clue of what the other hemisphere is doing.
- If you present only the word in the left visual hemifield and ask what the word is they don’t know…They will say they didnt see anything.
→ The left hand can point or select the spoon,not the right hand
Dichotic listening task
Normal controls
* Present two different sounds simultaneously in each ear
* When you ask the subject to say what they heard, most frequently they report (verbally) what they heard in the right ear → dominance left hemisphere is dominantt for language so it will naturally report what is presented in the right ear.
If asked to attend specifically to what is presented
to the left ear (or present a sound only in the left ear), can do it
→ Selective auditory attention
Patients with section of the Corpus callosum
→ Deficits to name what is presented to the left ear. Very difficult for them to attend to what is presented in the left ear. Cannot switch their attention to it because the info is not crossing the corpus callosum
Sperry’s human case - Example 4
Patient sees a word that is flashed, hald of the word is in the right visual field and the other half is in the left visual field
Ask split brain patient What is the word? Give a verbal answer of what they saw.
-They answer: “art”
- Ask the patient to point with the left hand–> Point with the left hand one of 2 cards HE or ART on it
-They point the card with: “He”
Conclusion: both hemispheres simultaneously saw a
different portion of the word
Chimeric Face test
Chimeric face: two different faces mixed together.
Flash chimeric face with two half different faces in each hemifield.
→ If you ask the patient to verbally tell you what they saw, the person said that they saw the women (what the left hemisphere saw).
→ If you ask them to point to the face they saw with their left finger, they would point to the man (what the right hemisphere saw).
→ The one hemisphere completes a symmetrical face
so both hemispheres ‘‘think’’ they saw a full face.
Explain Gazzaniga’s concept of the left-hemisphere interpreter
Gazzaniga and the concept of the “left-hemisphere
interpreter”.
* Experiment:
- show two pictures at the same time, one in each hemifield (right visual field = chicken, left visual field = winter scene).
- patient has to point with his two hands at pictures of two objects corresponding
→ left hand is pointing at the card with a picture of
a snow shovel (right hemisphere saw snow scene)
→ right hand is pointing at the card with a picture
of a chicken (left hemisphere saw chicken)
- Ask the patient why his left hand is pointing at the shovel:
‘’you use a shovel to clean out the chicken shed’’
→ the left hemisphere who will produce the answer to this question did not see the winter scene. So the answer of a split brain patient would say is ‘’you use a shovel to clean out the chicken shed’’. Left hemisphere will try and make up a verbal story that matches what is happening.
Generating emotional reactions
The two hemisphere need to be working together for emotional reactions. If you want to verbalize an emotion and the emotion is processed by the right hemisphere and you don’t have have communication between the two hemispheres, it becomes very hard.
Experiment:
* Present a funny picture to the right hemisphere (in left visual field):
Patient said she saw nothing when asked
But they did smile and chuckle.
When asked why you are laughing: ‘‘I don’t know, nothing….’’
→ the right hemisphere can’t describe what was seen but the emotional reaction is there .
What are the positive symptoms of being a split brain patient?
Some split-brain patients can:
* Draw different pictures with each hand simultaneously
* Do visual search tasks faster than controls
→ Experiments indicated that the separated hemispheres
were able to scan their respective hemifields independently
How do we know that the two hemispheres are working stimultaneously?
Working simultaneously
* Helping-hand phenomenon: the right hand that ‘knows’ the answer may try to correct the left hand.
* Cross-cuing: some language abilities in the right hemisphere, some language comprehension. The right hemisphere will try to correct the he answer if it knows the answer.
→Cross-cuing from one hemisphere to the other may also happen
In real life, thye are not forced to use one hand so they would just use the hand that knows the answer. In experimental settings, you will see that the hand that knows the answer will try to correct the other hand.
What experiment determined the cross-cuing.
Experiment
Simple: present a green or red flash to the right hemisphere (left visual field)
* The patient answers at chance level at first but improves when a second guess is allowed.
Why?
- If the answer guessed by chance (by the left ‘speaking’ hemisphere) is the good answer, the patient sticked to the answer
- If the answer is wrong: the right hemisphere hears the left hemisphere’s guess and cues the left hemisphere that it’s wrong by frowning or by a shake of the head (try to demonstrate non verbal cue from right hemisphere)
→ when the answer is said out loud, the right hemisphere (that saw the light) hears the answer and then is able to correct what the left hemisphere said.
Working simultaneously
- Experiments in monkeys
- Present something separately to each hemisphere (eye) at the same time
- Each hemisphere memorizes a different scenario: each hemisphere can learn the two tasks.
Left eye: learns that if press the button with the cross → food
Right eye: learns that if press the button with the circle → food
→Learned those two associations in the same time it takes a normal monkey to learn one
→When CC sectioned: Evidence that each hemisphere acts as an only brain
Lateralisation of functions
These studies have helped us understand the brain specialization and lateralization of function.
- Controlateral motor control (lateralized)
- Left hemisphere: language and speech
- Right hemisphere:
- musicn (prosody)
- spatial processing
- visuo-motor tasks
- emotional processing
The right hemisphere
- Visual-constructional tasks: the right hemisphere is
better - When asked to draw the example, even if the splitbrain patient is right-handed, better with the left hand because if they use their right hand it is the left hemisphere that controls the right hand. The left hemisphere is not good for spatial analysis and spatial construction.
Block design test
Right hemisphere
you need to reproduce either a 2D picture or 3D construction with blocks. It is really a spatial visual task. Segment the picture into squares that you see and visualy match the picture with tthe blocks.
* Spatial awareness
* Block Design task
* Better performance with the left hand because right hand is not as good because it is controlled by the left hemisphere.
What happens when Joe is showed a word on the left side?
Word flashes to left side and his right hemisphere sees nothing. He says that he cannot see anything. When asked to draw it (LH) he realizes that it was a phone, because he draws a phone and then his left hemisphere can see the drawing and say what it is.
The face hemisphere and Joe
The right hemisphere (left field): focusing on the face
The left hemisphere (right field): focusing on the fruits that make the face
Structure-Function relationship
Correlations
-IHTT and bimanual coordination associated with different parts of the corpus callosum in each group.
In typical individuals the faster the intrahemispheric transfer time or the beter their bimanual coordination = the bigger their CC (specifically in the motor areas and parietal areas).
In autistic patients, the correlation between the behavioral measure was with the splenium
Conclusion of Autism study
Despite structural reductions in the corpus callosum:
→Intact information transfer (behavioral measures)
Hypothesis: They compensate by recruiting the fibers of the posterior part of the CC
* Transfer at the visual level rather than at the motor level
* Consistent with the literature
* Occipital (visual) over activations
* Modified structure-function relationship associated with equal performance→reallocation→different neuronal trajectories (they recruit a different brain network that is different than typical individuals)
When autistic people do something, they use their occipital areas more than the typical population. They rely on their sensory processing more than on frontal areas. Ravens processing matrices (reasoning task that uses visual info, resolve a visual puzzle). Autistic individuals are as good as normal individuals at the task but they recruit their visual areas more (recruit different area).
Ideational and conceptual apraxia
- When manipulation of tools is needed (difficulty sequencing their actions or using the tool for the correct purpose).
- Affects both spontaneous and on command
gestures - The basic gestures are ok but the meaning of it is incoherent
- Patient seems like they don’t remember how to use of objects
- Lost the meaning of how to use an object in their every day life.
Caused by lesions generally affecting the parietal temporal junction.
Geschwind’s explanation of the apraxias
Verbal command to Wernicke (left) then 2 possible trajectories:
1) From Wernicke to Left premotor region then CC to Right premotor then R precentral motor cortex – Left hand moves. (to control left and right hand?)
2) From Wernicke to corresponding ‘Wernicke’ in the Right hemisphere, then to R premotor to R motor region. (to contril just the left hand?)
* How do we know #2 is not the preferred way? Because damage to that area (posterior part) of the CC does not lead to apraxia (very rarely)
* But anterior CC lesion (wernicke area) yes, difficulties performing a motor gesture following a verbal command BUT, not when examiner mimes→no need for verbal comprehension as the patient can SEE
* Lesions in the dotted line (2nd picture) to the CC would cause left hand apraxia. BUT researched showed that a lesion to the solid line CC caused left hand apraxia demonstrating that the #1 pathways is the preferred way.
Case #1: Damage to the Corpus Callosum
leands to apraxia
- Lesion in CC, especially in the part of the CC connecting the bilateral motor areas.
- Can carry commands with the right arm (only problems in LH), ex: show me how you comb your hair…
- Comprehension intact - But with the left arm… incorrect (Left hand apraxia - everything is intact in left hemisphere but when it tries to go to right hemisphere (which controls the left hand) issues due to CC lesion).
- Can do those tasks in normal life (ex: use tools, combs, etc) or imitate the gestures — it is just when given a command that they cannot do these.
- Right motor area does not get the instructions from left motor area to perform the gesture.
However..
* Can do face movements if asked, like to blow a candle
* The face area of the motor cortex can control the cranial muscles on both sides of the face
* The left cortical face area does it
Controlled by tthe two hemispheress so its hard to just move one side of the face. The Left motor area controlling the mouth can control both sides of the mouth muscles.
Case #2: damage to the left premotor region
Facial apraxia
* Lesion affecting the motor area and Broca (connectivity). Lesion in the left premotor area (ventral part of the motor cortex. (could alsonhave broca’s aphasia)
→Cannot carry out facial movements
* Information from the left Wernicke’s area cannot reach the left ventral premotor cortex (PMC) because it is destroyed
* The lesion also destroyed the origins of the callosal fibers connecting L premotor cortex from the Right PMC
Case #2: Dmage to the left premotor region.
Sympatehic Apraxia: if the lesion is a little bit bigger and also involved other parts of the motor cortex.
* A type of ideomotor apraxia (of the left hand)
* Posterior language comprehension area is intact
* Lesion around the left frontal areas disconnecting the left posterior areas from the right premotor cortex so that “the instructions” for the left hand cannot reach the hand area of the right frontal lobe
* Right arm paralysed - because the motor area for the hand is essentially lesioned
* Left arm apraxic:
→Right motor cortex is intact so the Left arm can move but the right motor cortex does not receive the command from the Left motor cortex through the CC
→inability of the non pathologic hand to carry out commanded movements
* Left hemisphere dominance for skilled movement (in right handed)
Case 3: lesion to Wernicke’s area
- Patient fail to respond to verbal command (cannot do the gesture/ command)
* Deficit in comprehension
* Not apraxia
Case 4: damage in the connections between Wernicke and the premotor area
- Intrahemispheric
- Also show conduction aphasia (affect the arcuate fasciculus, sentence repetition problems)
- If lesion not near the precentral motor cortex: no paralysis
- Following verbal commands: patient unable to carry movement with the right limbs or the left limbs because if the info does not reach the left motor area and cannot be transferred to the right by the CC
- Also facial apraxia (auditory instructions do not reach the left motor cortex)
The descending tracts
Pyramidal tract
- Corticospinal tract
- Voluntary movement and control of the musculature of the opposite side of the body
- About 90% decussate (cross the midline of the body): control of limbs
→Lateral corticospinal tract
- About 10%: do not decussate at the pyramids, they
continue ipsilateral: control of trunk, neck etc. The ones that stay ipsilateral innervate the axial muscles. N →Anterior corticospinal tract
- Axial muscles also have an input from other cortical areas than the motor cortex→extrapyramidal tract
What is axial control?
- Movements of the body trunk involve both sides of the body.
- The anterior (ventral) corticospinal tract:
- Is responsible for controlling the muscles of the body trunk.
- Is influencing both sides of the body to coordinate postural muscles in broad movements of the body.
- These axons do not decussate in the medulla.
- They remain in an anterior position as they descend the brain stem and enter the spinal cord.
- Upon reaching the appropriate level in the spinal cord, the axons decussate and synapse with their corresponding lower motor neurons.
- The lower motor neurons are located in the medial regions of the ventral horn, because they control the axial muscles of the trunk.
- Coordinating axons that are often considered bilateral, as they are both ipsilateral and contralateral.They can control each side a little bit.
Extrapyramidal System
- Maintaining posture and regulating involuntary motor functions (more for involuntary control).
- Posture, tone, gate (things that are more automatic)
- Control of automatic modifications of tone and movements
- Mostly from brain stem and sometimes the crebellum
- Example of a lesion in lower parietal areas can prevent the information from reaching the pyramidal system: cannot carry limb movement
- But commands for trunk motion can be performed
Ex: to bow, which can be achieved by the non pyramidal system directly from Wernicke’s area and basal ganglia
In some way for those very simple commands, the brainstem and the more subcortical areas, can get input directly from Wernickes area or from motor control areas. This is why some kind of motor aspect of the command can still be performed.
The tracts
all the other tracts make up the extrapyramidal system
Ideomotor apraxia summary
Corpus callosum
* Lesion in anterior corpus callosum (lesions to the posterior part usually do not lead to ideomotor apraxia)
* Can carry verbal commands with right hand but will fail with the left hand
* Can imitate perfectly (disturbance as the result of disconnection of the speech area from the right motor area)
Left frontal
Lesion in Left motor association cortex which also disconnects it from the R motor region:
* Right hemiplegia and Broca’s aphasia
* Failure to carry out verbal commands with the intact left hand (LH is apraxic)
→Sympathetic apraxia
* No comprehension deficits
if the lesion is big enough to reach the hand area, other limbs will be affected.
Parietal
Lesion in Left arcuate:
* Failure to carry out correct motor commands with EITHER left or right limbs
* No elementary motor problem
* Normal comprehension
* both right and left limb apraxia
- A parietal lesion around the arcuate fasciculus can also affect fibres from the visual cortex so both verbal command and imitation would be affected
- Motor pathway is also mostly left lateralised (in right-handed) but some patient seem to make use of the right pathway and still be able to imitate
- Some patients will be less affected at the motor level and more at the imitation level.
Temporo-parieto-occipital junction
- Extensive lesions
- Semantic information
→Ideational apraxiaWith larger lesions, bilateral and involving several regions, leads more to ideational and conceptual apreaxia.
The Rey Osterrieth complex figures
On the left is the template they see what theey have to reproduce.
The Rey Osterrieth complex figures (continued)
Sometimes we see constructional apraxia in the LH
Left Hemisphere region, elements are all there, spatially at the correct location but the motoric aspect is not as good.
Right hemisphere lesions: lack of accurate spatial relations between components of objects and an incoherent, disjointed quality
* Patients do not necessarily fail to notice or copy individual elements and do not have distinctly lateralized impairments as in neglect (but can also have left neglect)
→The correct spatial relationships between items are lost and elements are transposed to different positions or orientations.
Do not forget elements, but place them att the wrong location.
can have hemineglect
Left hemisphere lesions: oversimplified, reduced details, visual cues help them
* Usually no hemineglect
→The right hemisphere posterior parietal area still receives the information by interhemispheric connections and can compensate.
* But can have agraphia etc…
Left→motoric executive aspects
Right→perception of spatial relationship: visuospatial impairment
LESION CASE STUDY
Right parietal lesion
Right parietal lesion
* Very hard time to reproduce images, the more complex = the harder.
* Patient failed specifically at representational tests, which imply the ability to conceptualize complex spatial relationships.
* Independent of elementary visuo-perceptual and executive impairments.
* Supports the idea that, between the visuo- perceptual analysis and the realization of graphic output, some intermediate stages of drawing exist, at which information is processed to prepare and guide motor output –> somehwere in between where the parietal lobe is and before motor output.
Parietal lesion left vs right
Every patient is different - but u can se a general pattern. This is what they concluded by many studies
LPL: better spatial aspect
RLR: woese spatial and reproducong pattern correctly (this case also had hemineglect).
