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Speech and language are of fundamental human significance, both in social interaction and in private intellectual life. When they are disturbed as a consequence of brain disease, the functional loss exceeds in many ways all others in gravity—even blindness, deafness, and paralysis. The neurologist is concerned with all derangements of speech and language, including those of reading and writing because they are almost invariably manifestations of disease of the brain.

Viewed broadly, language is the means of symbolic representation of objects, actions, and events and, therefore, the mirror of all higher mental activity. The internal manipulation of these symbols constitutes thinking and their retention is the substance of memory. In a narrower context, language is the means whereby patients communicate their complaints and problems to the physician and at the same time, the medium for all delicate interpersonal transactions. Consequently, any process that interferes with speech or the understanding of spoken words touches the very core of the physician–patient relationship. Although speech and language are closely interwoven, they are not synonymous. Language refers to the production and comprehension of words, whereas speech refers to the articulatory and phonetic aspects of verbal expression. A disruption of language function is always a reflection of an abnormality of the brain and, more specifically of the dominant cerebral hemisphere. A disorder of speech may have a similar origin, but not necessarily; it may be a result of abnormalities in the brain or to laryngeal, pharyngeal, or lingual mechanisms.

Finally, the study of language disorders and the development of language (see Chap. 27) serve to illuminate the relationship between psychologic functions and the anatomy and physiology of the brain.


It has been remarked that as human beings, we owe our commanding position in the animal world to two faculties: first, the ability to develop and employ verbal symbols for ideation and as a means of transmitting thoughts by spoken and written word, and second, the remarkable facility in the use of our hands. One curious and provocative fact is that both language and manual dexterity (as well as praxis) have evolved in relation to particular aggregates of neurons and pathways in one cerebral hemisphere (the dominant one). This is a departure from most other localized neurophysiologic activities, which are organized according to a contralateral or bilateral and symmetrical plan. The dominance of one hemisphere, usually the left, emerges in brain development together with speech and the preference for the right hand, especially its use for writing. It follows that a lack of development or loss of cerebral dominance as a result of disease disrupts both these traits, causing aphasia and apraxia.

There is abundant evidence that higher animals are able to communicate with one another by both vocalization and gesture. However, the content of their communication is seemingly their feeling or reaction of the moment. This ...

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