| |
Abstract:
Developmental dyslexics are characterized by impairments of
phonological awareness and verbal working memory. Recent results
demonstrated the involvement of the left-sided perisylvian regions
in normal phonological processing. Using PET, brain activations
during word and pseudo-word repetition tasks were studied in 6
developmental dyslexic subjects and 6 controls matched for age
(mean 25.3 vs 29.0, respectively), university level, and global IQ
(133.1 vs 127.4, respectively; only verbal IQ was higher in
controls (139.8 ± 10.6) than in dyslexics (122.0 ±
6.9)). Although performance in dyslexics on specific language tests
were significantly worse than in controls, performance were similar
on repetition tasks during PET scanning. Twelve scans were
acquired, 4 for repetition of words, 4 for pseudo-words and 4 'at
rest'. PET results were analyzed using SPM96 and a factorial design
in which interactions were investigated between across-task and
across-group effects. This analysis revealed that dyslexics
activated more the inferior part of the prefrontal cortex in both
hemispheres compared to controls (x,y,z=40,16,6 and -26,32,-26, Z
scores=4.31 and 4.15, respectively). In controls, weaker
activations were observed in Wernicke's area for word repetition
(x,y,z=-28,-34,22, Z score= 3.28) and right prefrontal cortex
(x,y,z=44,16,46, Z score= 2.96) for non-word repetition. This study
demonstrated for the first time that repetition tasks in dyslexics
recruited over-activations in lower parts of the prefrontal cortex,
probably reflecting peculiar memory-related and attention-related
processes that might make the tasks feasable, although especially
effortful.
|
