Alexia and the neural basis of reading.

Three main types of acquired reading disturbance (alexia) have been described and accepted by clinicians. Each features a group of distinct findings and each is found following damage to a separate location within the language dominant hemisphere of the brain. Many different names have been applied to these entities, but posterior alexia, central alexia, and anterior alexia appear to represent both the clinical differentiations and the basic anatomical loci. A fourth type of acquired alexia, called deep dyslexia, has recently been reported, again with separate clinical findings and a different anatomical locus postulated. By comparison of the clinical features of the four alexias with features of alexia in Oriental languages and the reading competency of the nondominant hemisphere, a hypothetical neural basis for the act of reading can be outlined.