Lecture 17: Corpus callosum continued

effect of age

- callosotomies done in younger individuals:

> disconnection syndromes observed in split-brain adults not observed

> some deficits at first but they improve with time

> immature brain has great potential of adaptation after surgeries:

-> plasticity leading to cerebral reorganization

development anterior commissure

10th week of gestation

corpus callosum development

in utero from week 12 to 6/7th month

rostra-caudal development (genu first)

myelinization process continues after birth

agenesis of corpus callosum

- defect in neuronal migration

> before week 10: no AC and no CC

> between week 10 and 12: no CC (AgCC)

> between week 12 and 20: partial agenesis of CC

what happens when you are born without corpus callosum

> sometimes nothing

> split brain/disconnection syndrome not observed

> precocious plasticity mechanism

> normal IQ in 2/3 of cases

Kim peek

> agenesis of corpus callosum + other brain abnormalities

> autism

> low IQ

> incredible memory abilities

> able to read left and right page of book simultaneously

deficits

- motor coordination

- emotional

- social

- pragmatic language

possible adaptation mechanism

> bilateral language functions, some amytal sodium studies say it is not case

> residual commissures

residual commissures

-> anterior commissure, sub-cortical structures

-> compensation, especially to transfer visual information

-> ipsilateral tactile information

- normally eliminated in normal development

- each hemisphere has bilateral representation

case of Kim peek

> agenesis of corpus callosum + other brain abnormalities

> autism

> low IQ

> incredible memory abilities

> able to read left and right page of book simultaneously

agenesis of CC and autism

- motor, language, emotional and social deficits similar to characteristics of individuals on autism spectrum

- one of most consensual neuroanatomical characteristic observed in

autism-> volumetric and macrostructural reductions of CC

- between 10-30% of cases of Agenesis of CC have autism spectrum disorder diagnostic or marked autistic traits

anatomical connectivity and corpus callosum

white matter differences (frontal temporal and parietal)

- link between white matter alteration and function

> processing speed of brain

> motor deficits

> sensori-motor integration

- corpus callosum in autism

> reductions in volume & macrostructural alterations

altered inter hemispheric communication

objectives

- relate corpus callosum structure (microstructure and volume): MRI-> with function

> measure inter hemispheric transfer time: visuomotor task (Poffenberger)

> measure bimanual coordination: Purdue pegboard test

poffenberger paradigm

- Measures inter hemispheric transfer time (IHTT)

poffenberger paradigm question

> where does transfer occur in CC?

-> at visual level (dotted line)

-> at motor level (full line)

poffenberger paradigm answer

> manipulate motor and visual aspects in turn and see which affects transfer time

> localized CC lesions

-> transfer faster at motor level

corpus callosum structure

- results:

> size: AUT<TYP forntal and parietal

behavioral results

- no difference in terms of inter hemispheric communication:

> IHTT (poffenberger)

> bimanual coordination

structure-function relationship

- Correlations between behavioral measures and CC

- IHTT and bimanual coordination associated with different parts of corpus callosum in each group

corpus callosum study results

- despite structural reductions in corpus callosum:

> intact information transfer (behavioral measures)

- transfer at visual level rather than at motor level

- consistent with literature

> occipital (visual) over activations

- modified structure-function relationship associated with equal performance-> rellocation-> different neuronal trajectories

autistic motor deficits

- looking more closely at motor tasks

- Autistics:

> slower for unimanual conditions

-> reaction time: execution speed, anticipation, preparation of movement

intra-hemispheric connectivity deficits

> using spatial representation and integration of visual information essential to plan and execute movements

> role of parietal lobe: visuomotor integration, directed actions, imitation, plan and control of actions

intra-hemispheric connectivity

- importance of visual integration n motor defictis

- agrees with reduced intrahemispheric connectivity between frontal and parietal areas in autism

- atypical visual input and integration during motor action have been related with atypical connectivity between parietal and motor areas

apraxia

- first to describe this syndrome: Hugo Liepmann

- disorder of learned movement

- problem in organization of actions

- difficulty with movement is not caused by paralysis, weakness, or incoordination of muscles

- cannot be accounted for by sensory loss, comprehension deficits, or inattention to commands

ideomotor apraxia

difficult to imitate or act in response to verbal command

deficits in elementary gestures and production of movements

lesion disconnecting left auditory/visual from motor areas

damage too orpus callosum

- can carry commands with right arm

> comprehension intact

- with left arm… incorrect

- can do tasks in normal life or imitate gestures

geschwind apraxia

2 possible trajectories after command to Wernicke’s area

geschwind apraxia pathway (prefer)

W→L premotor area→CC→R premotor area→R precentral motor cortex = L hand moves

• goes through motor area of CC

• anterior lesion of CC causes apraxia

• only when examiner verbally commands, if they mime the patient can imitate, no need for verbal comprehension

geschwind apraxia pathway

L W→ R W → R premotor → R motor

• not preferred way

• goes through different part of CC

Case 1

damage to CC, Wernicke not damage but transmissions to R brain is

if verbal commands can be carried out with R arm→ comprehension intact

if patient tries with L arm, can’t do it

can do tasks in normal life or imitate gestures with no verbal commands

can do face movements if asked

Purdue pegboard test

measures bimanual coordination

peg two holes at same time

sequence of pegs