Intro arrow 10. Ectopia & Microgyrus arrow 10.2 Overview
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0. Left & Right Brain
1. Masking Alpha Channel
2. Rods & Cones
3. LGN: Magno & Parvo
4. SC: Superior Colliculus
5. Primary Visual Cortex
6. Dorsal - Ventral Stream
7. Eye Movements
8. Oculomotor System
9. Balance System
10. Ectopia & Microgyrus
11. Genetic Etiology
12. Reading
13. Animals
14. Conclusion / Solution
15. Different Theories
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10.2 Overview Brain abnormalities

A study published in 1991 by Harvard Medical School researchers (Margaret Livingstone, Albert Galaburda and colleagues) found anatomo-morphological correlations:

In the Cortical area:

  • Ectopias
  • Diffuse patterns of cortical scars
  • Dyslaminations

 

In the Cerebellar Cortex significantly larger cellular areas:

  • Medial Posterior Lobe
  • Anterior Lobe

 

Dysfunctions in several phonological cortexes:

  • Left Perisylvian
  • Left Temporal
  • Middle Temporal
  • Inferior Temporal

Altered functionality of processes(not directly involved in phonology):

  • Dysfunction of early sensory stages of the Magnocellular visual and auditory pathways
  • Dysfunctional visuospatial attentional system
  • Disorder of the motor system including altered cerebellar physiology

Other structural MR studies have shown inconsistent results: for example, the observation of Galaburda has been replicated only in 50% of the MRI studies. Anatomical measures of other structures such as the Corpus Callosum have also provided variable results:

  • Enlarged Splenium
  • Shrinkage in the Genu
  • Abnormally shaped Isthmus.


A Voxel-Based Morphometry (VBM) study, reported reduced grey matter in:

  • Orbital portion of the left Inferior Frontal Gyrus
  • Orbital portion of the Superior Temporal Gyrus
  • Outside the classical language regions.

The largest clusters were detected in:

  • Left temporo-Parietal-Occipital region
  • Left Inferior Gyri
  • Middle Temporal Gyri
  • Inferior Frontal Gyri
  • Superior Frontal Gyri
  • Superior Cerebellar regions bilaterally

No differences in white matter densities were reported, others reported 4 anatomical measures that differentiated phonological dyslexic subjects from reading-disabled and control subjects:

  • Marked rightward cerebral asymmetry
  • Marked leftward asymmetry of the anterior lobe of the cerebellum
  • Combined leftward asymmetry of the planum temporale and posterior ascending ramus of the sylvian fissure
  • Large duplication of Heschlís gyrus on the left

 

Others found significant morphological cerebral alterations in dyslexic children. In areas that showed significant correlations with reading, spelling and language measures:

  • Smaller right anterior cerebellar lobes,
  • Pars triangularis of the inferior frontal gyrus bilaterally
  • Overall brain volume


A recent VBM study, observed significant reductions of grey matter volume in areas of the brain associated with language and reading processing in people with a family history of dyslexia. Significant reductions were located bilaterally in:

  • Planum temporale
  • Inferior temporal cortex
  • Cerebellar nuclei
  • Left superior and inferior temporal regions

Finally, there is one MRI morphometric study on the cerebellum, found that, although normal controls had a larger right hemispheric cerebellar cortical surface, the cerebellar hemispheres in the dyslexic subjects were symmetric.

Conclusion: The coexistence of local cortical changes together with abnormality of cortico-cortical connectivity within the language neural network offers a realistic description of the neurology of dyslexia at a systems level and explains why tasks like reading or naming, which require the integration of multiple visual, phonological and articulatory codes, are sensitive in revealing a dyslexic brain.
 
 
 

The purpose of this site is to present questions and new ideas about the above subjects.

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