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Abstract:
Abstract: -- P. Celsis, K. Boulanouar et al. (Neuroimage, 9,
135-144 (1999)) used an Habituation-Recovery paradigm to
investigate the brain responses to tones and syllables in normal
subjects. The left superior temporal gyrus responded to acoustic
changes whereas the left supra-marginal gyrus (SMG) was
specifically implicated in the detection of phonological changes.
Here we show that the rate of deviants in syllable trains elicited
different responses in these regions in phonological dyslexics and
controls. Trains of 4 syllables were presented in blocks containing
0, 25, 50 or 75% of trains ending with a deviant syllable (/ta/ as
standard, /pa/ as deviant). Six normal s and 6 dyslexics were
studied using functional MRI and SPM96. Comparison between standard
trains and rest revealed a bilateral superior temporal pattern in
normals, whereas in dyslexics, activation s were mainly found in
the middle temporal gyrus. When opposing deviant to standard
trains, the left SMG was activated in normals, confirming our
previous result, but not in dyslexics. In both normals and
dyslexics, primary auditory areas showed a linear signal increase
with the rate of deviants. Auditory association areas showed an
inversed U-shape response in controls and a U-shaped response in
dyslexics. Thus, regions crucial for phonological processing are
less activated in dyslexics than in controls and, in addition,
present an abnormal response to changes in phonological information
in these patients.
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