1. Aphasia refers to loss of language ability due to brain damage, while alexia and agraphia refer specifically to impairments in reading and writing respectively. 2. Historical studies by Broca and Wernicke in the 19th century localized language functions to specific brain regions, which was later confirmed by modern imaging. 3. Lesions in different brain areas can cause different types of aphasia such as Broca's (non-fluent) or Wernicke's (fluent) aphasia, depending on whether expressive or receptive language is more impaired. Disconnection syndromes can also cause language deficits by disrupting connections between language areas.

1. Aphasia, Alexia, Agraphia and Disconnection Disorders William Wallis

11. Connections of “Speech Areas” Arcuate fasciculus and corpus callosum

22. Transcortical Aphasia A B When the regions of Broca, Wernicke and the arcuate fasciculus are intact (A), but surrounded by adjacent lesions (B), they are disconnected or isolated from their projection inputs. This results in various forms of aphasia, because of a disconnection from outside projections ( or area of concepts ) into A . The capacity to repeat, however, is relatively well preserved, as A is intact

23. Alexia without Agraphia The Ultimate Disconnection Syndrome Predict the Clinical Findings and Explain

24. Alexia without Agraphia 1 Right homonymous hemianopia Not aphasic and can write, as perisylvian area intact Cannot read as intact right occipital lobe is disconnected from dominant hemisphere by lesion in splenium of corpus callosum Relevant areas are supplied by posterior communicating artery Not to be confused with alexia and agraphia (usually angular gyrus lesion)

25. A Summary Alexia without agraphia Combination of a cortical lesion and a subcortical disconnection 1 Aphasias from lesions in projection cortex (Broca’s and Wernicke’s regions) Aphasia from subcortical disconnection or conduction aphasia Alexia with agraphia: lesion in angular gyrus or association cortex Transcortical aphasia isolates Broca’s and Wernicke’s regions and their connection