Is developmental dyslexia a disconnection syndrome? Evidence from PET scanning

Eraldo Paulesu, Uta Frith, Margaret Snowling, Alison Gallagher, John Morton, Richard S J Frackowiak, Christopher D. Frith

Research output: Contribution to journalArticlepeer-review

Abstract

A rhyming and a short-term memory task with visually presented letters were used to study brain activity in five compensated adult developmental dyslexics. Their only cognitive difficulty was in phonological processing, manifest in a wide range of tasks including spoonerism, phonemic fluency and digit naming speed. PET scans showed that for the dyslexics, a subset only of the brain regions normally involved in phonological processing was activated: Broca's area during the rhyming task, temporo-parietal cortex during the short-term memory task. In contrast to normal controls these areas were not activated in concert. Furthermore the left insula was never activated. We propose that the defective phonological system of these dyslexics is due to weak connectivity between anterior and posterior language areas. This could be due to a dysfunctional left insula which may normally act as an anatomical bridge between Broca's area, superior temporal and inferior parietal cortex. The independent activation of the posterior and anterior speech areas in dyslexics supports the notion that representations of unsegmented and segmented phonology are functionally and anatomically separate.

Original languageEnglish
Pages (from-to)143-157
Number of pages15
JournalBrain
Volume119
Issue number1
DOIs
Publication statusPublished - 1996

Keywords

  • Dyslexia
  • Functional brain imaging
  • Insula
  • Perisylvian regions
  • Phonology

ASJC Scopus subject areas

  • Neuroscience(all)

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