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Abstract:
In cognitive neuropsychological studies of reading, the
syndrome of deep dyslexia has received particular attention.
However, based on behavioural data, it has not been possible to
resolve whether the reading pattern in deep dyslexic patients
reflects imperfect functioning of remaining systems used for normal
reading or limited reading skills of the intact right hemisphere
which would be latent in normal reading. We studied
magnetoencephalographic (MEG) changes in cortical activity in a
chronic Finnish-speaking deep dyslexic patient during single-word
and sentence reading. In our patient and in most fluent readers,
the left superior temporal cortex was involved in lexical-semantic
processing, i.e., activation was stronger to semantically anomalous
than to appropriate sentence-final words (N400 effect). Activations
around this same cortical area could be identified in single-word
reading as well. Our data are thus in conflict with the right
hemisphere reading hypothesis, and rather suggest that in our
patient, reading-related lexical-semantic analysis was dependent on
the remaining left hemispheric structures. By performing repeated
recordings one year apart, we were also able to document
significant variability in both spontaneous activity and evoked
responses in the lesioned left hemisphere even though behaviorally,
the patient's performance was stable. The observed variability
shows the importance of estimating consistency of brain activity
both within and between measurements in brain-damaged
individuals.
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