Causes
Alexia typically occurs following damage to the dominant hemisphere of the brain which is usually the left. It can also occur with lesions to the occipital and/or parietal lobes, which are responsible for processing auditory, phonological and visual aspects of language. The region at the junction of occipital and temporal lobes (sometimes called the occipito-temporal junction) coordinates information that is gathered from visual and auditory processing and assigns meaning to the stimulus. Alexia can also occur following damage to the inferior frontal. Damage to these different areas of the cortex result in somewhat different patterns of difficulty in affected individuals. In some cases, a stroke can cause alexia.
Alexia without agraphia is classified as a disconnection syndrome which involves a disruption of the communication pathways between the left and right cerebral hemispheres. The right visual cortex receives information from the left side of the visual field, and this information must then be transferred through the posterior commissure and splenium of the corpus callosum to the word form system in the left hemisphere. In people with alexia without agraphia, this transfer of information is interrupted. The presence of agraphia is a result of lesions to the left posterior frontal lobe and left superior parietal lobe.
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