DOMINANT HEMISPHERE LANGUAGE DYSFUNCTION
Aphasia, a disorder of language usage and comprehension, should be distinguished from dysarthria, impaired articulation, and mutism, the absence of speech. Usually, the presence of aphasia accurately localizes dysfunction to the cerebral hemisphere concerned with speech.
To classify an aphasia, it is necessary to determine whether the patient can (1) speak fluently, with normal articulation and rhythm and without paraphasic, syntactic or grammatical errors or use of circumlocutory phrases; (2) accurately repeat spoken sounds, words, and phrases; (3) understand spoken language, as evidenced by accurate responses to spoken questions and ability to follow spoken commands (failure to follow a command may also be due to apraxia or paralysis and does not necessarily reflect poor comprehension); (4) consistently name common objects, presented visually, verbally, or tactilely; (5) read aloud accurately and with comprehension; (6) name words spelled aloud; and (7) write legibly and grammatically.
In transcortical aphasia, repetition of spoken language is preserved. Transcortical motor aphasia is a subtype in which there is a primary inability to produce spontaneous speech, but the ability to understand spoken language is retained. Transcortical sensory aphasia is a subtype that is characterized by a failure to understand spoken language; a transcortical sensory aphasia usually indicates a lesion deep in the basal ganglia or in the para- median frontal lobe. Patients with Gerstmann syndrome have difficulty with naming of fingers, left-right orientation, calculation, constructional drawing, and writing. The lesion causing the disorder is usually located in the angular gyrus of the dominant hemisphere. The angular gyrus has been implicated in different aphasia forms. This can be due either to its actual role in language or by creating, when damaged, a disconnection syndrome. Disconnection syndromes in general can present in fascinating, well-defined ways. One of the most famous language disconnection syndrome is the alexia without agraphia syndrome, in which patients can write but not read. This is most commonly seen as a consequence of left occipital strokes that damage the visual cortex on the left and also perturb the transfer of visual information from the right occipital visual cortex to the usually language-dominant left hemisphere.