Ordinary and extraordinary brain development: Anatomical variation in developmental dyslexia

Eight brains, six male and two female, of reliably diagnosed cases of developmental dyslexia have been analyzed in this laboratory thus far. Common to all the specimens is the absence of ordinary asymmetry in the planum temporale, a language relevant area of the temporal lobe. In addition, the male cases and one female case displayed multiple focal areas of malformation of the cerebral cortex, located variably in the language relevant perisylvian regions and to a greater or lesser extent bilaterally. Both female cases and, to a mild degree, one of the males display focal areas of cortical scarring dated to the end of pregnancy through to the end of the second year of life at the latest. The scarring tends to be located in the vascular watershed territories.Experimental animal research suggests that symmetry may represent absence of the necessary developmental pruning of neural networks required for specific functions such as language. This diminished pruning results in excessive neurons and (at least interhemispheric) connections.Additional modeling in experimental animals suggests that cortical malformations and scarring similar to those seen in the dyslexic brains may represent early focal injury that could be attributed to congenital disorders of the immune system.