Transcript Plasticity of Language-Related Brain Function During
Plasticity of Language-Related Brain Function During Recovery from Stroke
K.R. Thulborn, P.A. Carpenter, & M.A. Just By Sydney Schnell
Overview
Introduction Hypothesis Procedure Results Discussion Personal Opinion Summary for Final
Language and the Brain
Development of language involves many areas of the brain
Superior Temporal Gyrus (Wernicke’s Area)
Inferior Frontal Gyrus (Broca’s Area)
Aphasia – language disorder, inability to understand or express speech due to brain damage Wernicke’s Aphasia: meaningless, fluent speech Broca’s Aphasia: difficulty articulating words
Broca’s Area & Wernicke’s Area
Broca’s area highlighted in blue, Wernicke’s area highlighted in green
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
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
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
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 Broca’s area Case 2 34 year old male Epileptic, suffered stroke during surgery in left temporal lobe Damage to Wernicke’s area
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 Broca’s and Wernicke’s areas
Results: Normal Condition
Results: Case 1
Activation maps at a. 76 hours after stroke and b. 6 months after stroke Broca’s area showed strong right dominance at 76 hours, leading into complete right dominance by 6 months Wernicke’s area remained completely left dominant
Results: Case 2
Activation maps at a. before stroke (with epileptic focus), b. 3 months after stroke, and c. 9 months after stroke
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
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
My Opinion…
Positive 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
Negative Aspects
Very small sample size One of the focal case studies did have a previous condition that could have influenced the redistribution pattern Short discussion
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