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A functional neuroimaging description of two deep dyslexic patients
C J Price1, D Howard, K Patterson
1Wellcome Institute of Neurology Department of Cognitive Neurology London UK 12 Queen Square WC1N 3BG, UK.
Journal of Cognitive Neuroscience
|December 31, 1998
Summary
Deep dyslexia, a reading disorder from left-hemisphere damage, involves semantic errors. Brain imaging shows this disorder primarily uses spared left-hemisphere regions for word meaning and naming, not right-hemisphere processing.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Neurolinguistics
Background:
- Deep dyslexia is a reading disorder characterized by semantic errors, resulting from left-hemisphere brain damage.
- Two main hypotheses explain deep dyslexia: residual left-hemisphere function or right-hemisphere processing.
Purpose of the Study:
- To investigate the neural underpinnings of deep dyslexia using functional anatomy mapping.
- To adjudicate between the left-hemisphere residual system and right-hemisphere processing hypotheses.
Main Methods:
- Functional magnetic resonance imaging (fMRI) was used to map brain activity in two deep dyslexic patients (CJ and JG) during reading tasks.
- Brain activation patterns were compared between deep dyslexic patients and a control group.
Main Results:
- Deep dyslexic patients showed normal or enhanced activity in left-hemisphere regions crucial for naming (Broca's area) and word meaning (temporal and parietal cortex).
- Right-hemisphere activation was inconsistent in both patients and controls, with some differential activation observed in patients.
- Activation patterns predominantly reflected semantic and phonological processing in preserved left-hemisphere areas.
Conclusions:
- Deep dyslexia is primarily explained by the function of spared left-hemisphere semantic and phonological systems.
- The findings preclude an explanation of deep dyslexia based solely on right-hemisphere word processing.