Intro arrow 10. Ectopia & Microgyrus
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0. Left & Right Brain
1. Masking Alpha Channel
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5. Primary Visual Cortex
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7. Eye Movements
8. Oculomotor System
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10. Ectopia & Microgyrus
11. Genetic Etiology
12. Reading
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10.1 Ectopia & Microgyrus

Albert Galaburda and his team of Harvard Medical School noticed that, next to a more symmetric Plana Temporale and differences in the LGN, that language centers in dyslexic brains showed microscopic flaws known as Ectopias and Microgyria. These flaws affect connectivity and functionality of the cortex in critical areas related to sound and visual processing. These structural abnormalities may be the basis of the inevitable and hard to overcome difficulty in reading.

In medicine an ectopia is a displacement or malposition of an organ of the body. Most ectopias are congenital but some may happen later in life. The ectopias in the cortical area of the brain, are a pathological collection of neurons that have pushed up from lower cortical layers into the outermost layer. These ectopias are produced before six months of gestation when there is a breach in the pial-glial border which normally prevents neurons from migrating too far.


They are somekind of brain ‘warts’ found particularly clustered round the left temporoparietal language areas.

 One consequence of dysplasias and ectopias is reduced connectivity between neighbouring regions. This was shown to be the case in newborn rats in which the pathology was experimentally induced, it leaded to thalamic changes and behavioral deficits comparable to those seen in the dyslexics. This reduced connectivity also caused changes in areas, such as the left middle temporal gyrus. Analysis of the white matter data also showed abnormalities. Significant reduction of white matter density in dyslexia was seen within the arcuate fasciculus. This finding replicates diffusion tensor imaging data.

A microgyrus is an abnormally small, malformed convolution of the brain, it is an area of the cerebral cortex that includes only 4 cortical layers instead of 6.


A low power photomicrograph of a typical region of induced microgyria. In comparison to the adjacent undamaged cortex (right) with six layers, microgyric cortex has four layers. Layer i is contiguous with the molecular layer of the undamaged cortex and fuses to form a microsulcus (arrow). Layer ii is contiguous with layers II and III of undamaged cortex, but is unlaminated. Layer iii is a glial scar that is the remnant of the original injury. Layer iv is contiguous with layer VI b of intact cortex. Solid lines show borders of the microgyric area. (Bar = 200 mm. wm = white matter.)


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