Aphasia from a Neurolinguistic Perspective
Authors: Edwards Susan , Salis Christos 
Published: August 2016

Aphasia is an acquired language disorder subsequent to brain damage in the left hemisphere. It is characterized by diminished abilities to produce and understand both spoken and written language compared with the speaker’s presumed ability pre-cerebral damage. The type and severity of the aphasia depends not only on the location and extent of the cerebral damage but also the effect the lesion has on connecting areas of the brain. Type and severity of aphasia is diagnosed in comparison with assumed normal adult language. Language changes associated with normal aging are not classed as aphasia. The diagnosis and assessment of aphasia in children, which is unusual, takes account of age norms.

The most common cause of aphasia is a cerebral vascular
accident (CVA) commonly referred to as a stroke, but brain damage following traumatic head injury such as road accidents or gunshot wounds can also cause aphasia. Aphasia following such traumatic events is non-progressive in contrast to aphasia arising from brain tumor, some types of infection, or language disturbances in progressive conditions such as Alzheimer’s disease, where the language disturbance increases as the disease progresses.

The diagnosis of primary progressive aphasia (as opposed to non-progressive aphasia, the main focus of this article) is based on the following inclusion and exclusion criteria by M. Marsel Mesulam, in 2001. Inclusion criteria are as follows: Difficulty with language that interferes with activities of daily living and aphasia is the most prominent symptom. Exclusion criteria are as follows: Other non-degenerative disease or medical disorder, psychiatric diagnosis, episodic memory, visual memory, and visuo-perceptual impairment, and, finally, initial behavioral disturbance.

Aphasia involves one or more of the building blocks of language, phonemes, morphology, lexis, syntax, and semantics; and the deficits occur in various clusters or patterns across the spectrum. The degree of impairment varies across modalities, with written language often, but not always, more affected than spoken language. In some cases, understanding of language is relatively preserved, in others both production and understanding are affected. In addition to varied degrees of impairment in spoken and written language, any or more than one component of language can be affected. At the most severe end of the spectrum, a person with aphasia may be unable to communicate by either speech or writing and may be able to understand virtually nothing or only very limited social greetings. At the least severe end of the spectrum, the aphasic speaker may experience occasional word finding difficulties, often difficulties involving nouns; but unlike difficulties in recalling proper nouns in normal aging, word retrieval problems in mild aphasia includes other word classes.

Descriptions of different clusters of language deficits have led to the notion of syndromes. Despite great variations in the condition, patterns of language deficits associated with different areas of brain damage have been influential in understanding language-brain relationships. Increasing sophistication in language assessment and neurological investigations are contributing to a greater, yet still incomplete understanding of language-brain relationships.