Send to

Choose Destination
Proc Natl Acad Sci U S A. 1991 Sep 15;88(18):7943-7.

Physiological and anatomical evidence for a magnocellular defect in developmental dyslexia.

Author information

Department of Neurobiology, Harvard Medical School, Boston, MA 02115.

Erratum in

  • Proc Natl Acad Sci U S A 1993 Mar 15;90(6):2556.


Several behavioral studies have shown that developmental dyslexics do poorly in tests requiring rapid visual processing. In primates fast, low-contrast visual information is carried by the magnocellular subdivision of the visual pathway, and slow, high-contrast information is carried by the parvocellular division. In this study, we found that dyslexic subjects showed diminished visually evoked potentials to rapid, low-contrast stimuli but normal responses to slow or high-contrast stimuli. The abnormalities in the dyslexic subjects' evoked potentials were consistent with a defect in the magnocellular pathway at the level of visual area 1 or earlier. We then compared the lateral geniculate nuclei from five dyslexic brains to five control brains and found abnormalities in the magnocellular, but not the parvocellular, layers. Studies using auditory and somatosensory tests have shown that dyslexics do poorly in these modalities only when the tests require rapid discriminations. We therefore hypothesize that many cortical systems are similarly divided into a fast and a slow subdivision and that dyslexia specifically affects the fast subdivisions.

[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center