Cortical Plasticity

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Kennard did what?
Extensive research on both adult and child monkeys to investigate how the brain can recover from insult or lesion
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What is the young age plasticity?
The Younger the age or immaturity of the organism the greater the brain plasticity
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What was the Kennard 1936 study?
At 40 days old, a monkey had a bilateral lesion to the motor cortex. She declared that at the end of the first week after the operation it could walk and climb and feed itslef by approximating its mouth to the food rather than by using its hands
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Kennard 1936: what was reported to be the problem with children as well as adults?
Children had similar problems in releasing grasp as adults did 1 month after the lesion. Both groups would be unable to release grip from the roof bars and often hand there until down
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What did Kennard further highlight?
Dennis (2009): Kennard highlighted that while children could make a full or incomplete recovery it was also possible for adults to make full recoveries
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What did Kennard (1936) go on to suggest?
several factors that predicted outcome after early brain lesions such as; o Size of lesion o Time of injury/after injury o Site of lesion o Number of brain lesions
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What is age not?
A mechanism to explain plasticity but rather describe the outcomes of neurodevelopmental disorders or brain lesions
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Kramer (2004)
Neural plasticity does occur over the life span, although outcomes are demonstrated to decrease with age
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What is plasticity ?
An intrinsic property of the CNS, reflecting its capacity to respond in a dynamic manner to the environment and experience via modification of neural circuitry
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What is this phenomenon linked to?
Processes of brain development and function across the lifespan (Mosch et al, 2005)
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What does this suggest?
Children have greater sensitivity to plasticity within a critical to recover from a brain lesion. Adults recover less well after insult and therefore have less sensitive plasticity
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What do clinical observations suggest?
great variability in outcome from early brain insult highlighting that while children may indeed have great capacity for plasticity, but they can also experience poor recovery.
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For example (Anderson and Moore, 1995)
Children sustaining generalised cerebral insult were noted to experience slower recovery and poorer outcomes than adults
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What are the two stages suggested after recovery of a brain llesion?
Restitution and substitution
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What is restitution?
As the damaged brain heals, neural pathways are reactivated and functions are restored.
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What is substitution?
Recovery via transfer/reorganisation of functions from damaged brain tissue to healthy sites
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What do both of these tend to support?
BOTH of these tend to support the early vulunerability hypothesis rather than early plasticity hypothesis.
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What is the support for second recovery process?
Interhemispheric reorganisation: functions transfer to the analogous site in the non- damaged hemisphere
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Potential for intrahemispheric transfer is well illustrated by what?
a recent functional MRI study of children born pre-term identified to have diffuse cerebral pathology
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At 12 years, these children demonstrated different patterns of what?
functional connectivity within the left hemisphere to those of same aged healthy peers, with discrepancies reflecting frontal and temporal pathology identified on structural scans
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Hamilton (1999)
In blind individuals visual cortex is associated with braille reading, case of Braille Alexia, 63 year old woman, blind since birth, braille reader since 7, bilateral stroke, the lesion was at the back of the brain, not damaged somasematic section
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What was found about the pateint?
Normal neurological exam, including somatosensation  But unable to read Braille after stroke
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Therefore what was suggested?
The function had been substituted to the occipital cortex at an early period.
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Merabet et al (2008)
Inevestigated the effect of sudden, complete and prolonged visual deprivation (five days) in normally sighted adult individuals while they were immersed in an intensive tactile training program
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Following the five day period, how did pps perform?
blindfolded subjects performed better on a Braille character discrimination task
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What was found in the blind fold group after an fMRI?
fMRI scans revealed an increase in BOLD signal within the occipital cortex in response to tactile stimulation after five days of complete visual deprivation.
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What was found on the fifth day?
reversible disruption of occipital cortex function on the fifth day (by repetitive transcranial magnetic stimulation; rTMS) impaired Braille character recognition ability in the blindfold group but not in non-blindfolded controls
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When was this effect no longer evident?
After 24 hours
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From this evidence it would seem logical to conclude what?
both immature and late brains have similar plastic adaptability to substitute function
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Why is this not the complete picture?
studies that have specifically focused on assessing if early blind/ <16 years old at sight loss) show different structural changes compared to late blind and sighted controls
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If they did it would provide evidence of what?
a range of tactile processing tasks that early or congenitally blind patients show activation in the occipital lobe all the way up to V8 and the Mt area.
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Burton (2002)
Late blind only show recruitment up to V4
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Evidence of a critical period in vision can be observed in studies showing what?
studies showing congenitally blind patients performing better than sighted or late blind subjects when body representation cues are put in conflict (I.e. tasks where pps cross arms).
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What does the adult brain have?
also susceptible to maladaptive plasticity, Phantom Limb and Phantom Limb pain
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Dennis (2003)
He argued that a fully plastic brain maintains an equilibrium (with a homeostatic unchanging stable brain
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What are maladaptive outcomes the result of?
disequilibrium
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In relation to the question he would argue what?
immature brain is vulunerable to increased maladptive plasticity because of some of the mechanisms that drive development
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Patient DR
Hand transplantation: Traumatic amputation of his non dominant left hand at age 23. Allogeneic transplant at age 36.
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What was found?
- He hasn’t had a limb for 13 years, therefore, that is a long time for structural reorganisation of the somatosensory cortex. However, shortly after the transplant he is able to hold and move playing cards
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Grip Test
- 3 different cubes: 1 cm, 2 cm and 3 cm cube - The grip aperture scales to the size of the object - The grip aperture scales before you even make contact with the object
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What was found?
- At post-transplant 26 months, There is more activity in the motor cortex and somatosensory cortex. However in healthy controls, there was activation in the cerebellum - There are much stronger activations in the patient at 41 months
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There is also what?
Cerebellar activation that wasnt there previously. - Within the normal range: Dr’s grasp related activity is similar to that of healthy controls
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The reattached hand won't what?
have all the nerves and blood vessels that were originally connected before the accident.
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What is swallowing?
critical to human survival because it involves the regulation of airway protection and oral nutrition
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What does dysphagia refer to?
disordered swallowing associated with central and peripheral sensorimotor deficits associated with stroke, neurodegenerative disease, tumours of the head and neck, infection or trauma
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Kleim et al (2002)
Cortical loss can occur without training as the movements formerly represented in the lesioned zone do not reappear in adjacent cortical regions. Failure to drive specific brain function through training can lead to further degradation of a functio
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How are patients with dysphagia fed?
Through a feeding tube and even expectorate their own saliva rather than swallow
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What does disuse of the swallowing mechanism may diminish?
- Disuse of the swallowing mechanism may diminish its cortical representation and poses a threat to functional recovery in the long term
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PAtients with oropharyngeal dysphagia and life threatening shoudl be offered what?
systematic swallowing drills but without using a bolus
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The goal would be to improve their swallowing skill, how?
Repetition: will help preserve cortical and subcortical representation and make the patients return to oral nutrition easier and faster.
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Hamdy et al
conducted a 3-month follow-up study of patients after their first-ever unilateral hemispheric stroke and dysphagia
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They showed what?
those patients who spontaneously recovered swallowing function had increased cortical representation of pharyngeal musculature in the intact (contralateral) hemisphere
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Patients who continued to be dysphagic showed what?
correspondingly displayed no change in their cortical representation patterns
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What did these findings show?
functional recovery was associated with permanent reorganisation of the contralateral unaffected cortex
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Where no recovery of swallowing showed?
Enlargement of representation did not occur
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Other cards in this set

Card 2

Front

What is the young age plasticity?

Back

The Younger the age or immaturity of the organism the greater the brain plasticity

Card 3

Front

What was the Kennard 1936 study?

Back

Preview of the front of card 3

Card 4

Front

Kennard 1936: what was reported to be the problem with children as well as adults?

Back

Preview of the front of card 4

Card 5

Front

What did Kennard further highlight?

Back

Preview of the front of card 5
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