Plasticity of Language-Related Brain Function During Recovery from Stroke

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Plasticity of Language-Related Brain Function
During Recovery from Stroke

• K.R. Thulborn, P.A. Carpenter, M.A. Just

By Sydney Schnell
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Overview

• Introduction
• Hypothesis
• Procedure
• Results
• Discussion
• Personal Opinion
• Summary for Final

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Language and the Brain

• Development of language involves many areas of
  the brain
• Superior Temporal Gyrus (Wernickes Area)
• Inferior Frontal Gyrus (Brocas Area)
• Aphasia language disorder, inability to
  understand or express speech due to brain damage
• Wernickes Aphasia meaningless, fluent speech
• Brocas Aphasia difficulty articulating words

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Brocas Area Wernickes Area

• Brocas area highlighted in blue, Wernickes area
  highlighted in green

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Language and the Brain

• Left hemisphere dominates language comprehension
• Neuroplasticity during development enables the
  right hemisphere to assume control when the left
  hemisphere is damaged
• PET scans of adult patients have demonstrated
  right hemispheric activation for language
  processing

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Experimental Motivation

• All previous studies were completed well after
  recovery from stroke and clinical symptoms
• Experimental Purpose Map the temporal evolution
  of anatomic and functional changes in
  language-related brain regions during recovery
  from aphasia after stroke

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Hypothesis

• Recovery is associated with a redistribution of
  workload over an existing large-scale network
• Immediate redistribution occurs to allow rapid
  initial recovery within days, followed by a
  consolidation of the new pattern over many months

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Subjects

• Control group
• Six healthy, male college graduates
• Aged 26 to 31
• Case 1
• 45 year old male
• Suffered from a left MCA stroke
• Damage to Brocas area
• Case 2
• 34 year old male
• Epileptic, suffered stroke during surgery in left
  temporal lobe
• Damage to Wernickes area

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Procedure

• Language comprehension was tested through 5
  cycles of 2 conditions
• 1. Central fixation, 30 seconds
• 2. Silently reading simple sentences, 30 seconds
• Mean length of the sentences 5.5 words
• Each cycle was followed by a true or false
  question, answered by pushing 1 of 2 finger
  switches
• Paradigm activates both Brocas and Wernickes
  areas

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ResultsNormal Condition
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ResultsCase 1

• Activation maps at a. 76 hours after stroke and
  b. 6 months after stroke
• Brocas area showed strong right dominance at 76
  hours, leading into complete right dominance by 6
  months
• Wernickes area remained completely left dominant

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ResultsCase 2

• Activation maps at a. before stroke (with
  epileptic focus), b. 3 months after stroke, and
  c. 9 months after stroke

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Discussion

• Spontaneous redistribution of function to the
  right hemisphere, within days of injury and
  continuing over subsequent months
• Focal brain damage and recovery results in a
  change to the large-scale network associated with
  such cognition
• When a key component to a cortical network is
  damaged, contralateral homologs are recruited to
  adopt the workload
• Long-term adaptations imply plasticity associated
  with recovery of language function
• Organizational flexibility of higher-level
  functioning systems

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Limitations Future Experiments

• Small sample size
• All men, no women
• Only two individuals recovering from a stroke
  were observed
• Redistribution pattern may not generalize to the
  recovery of non-epileptic patients
• Further experiments necessary on a wider
  population
• Information can be used to design future
  rehabilitation strategies for stroke victims that
  utilize the organizational flexibility of the
  cortical system

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My Opinion

• Positive Aspects

• Negative Aspects

• Very detailed, concise
• Fortunate to have MRI imaging for one patient
  prior to the stroke
• Before and after effects
• Well organized and easy to understand

• Very small sample size
• One of the focal case studies did have a previous
  condition that could have influenced the
  redistribution pattern
• Short discussion

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Summary

• A redistribution of function was consistently
  seen from the damaged area in the left hemisphere
  to the homologous structure on the contralateral
  side
• Redistribution begins within days of the injury,
  and solidifies over subsequent months
• Only the damaged regions within the cortical
  network were redistributed
• Full recovery of language function was observed

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Thank you!

• Questions??