Plasticity of Language-Related Brain Function During Recovery from Stroke

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

By Sydney Schnell

OverviewIntroductionHypothesisProcedureResultsDiscussionPersonal OpinionSummary 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 damageWernicke’s Aphasia: meaningless, fluent speech

Broca’s Aphasia: difficulty articulating words

Broca’s Area & Wernicke’s AreaBroca’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

SubjectsControl group

Six healthy, male college graduatesAged 26 to 31

Case 145 year old male Suffered from a left MCA stroke Damage to Broca’s area

Case 234 year old male Epileptic, suffered stroke during surgery in left temporal lobe

Damage to Wernicke’s area

ProcedureLanguage comprehension was tested through 5 cycles of 2 conditions

1. Central fixation, 30 seconds2. 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

DiscussionSpontaneous 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??