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

Thank you! Questions??