2. Disturbances of speech and language with diseases that globally affect higher-order mental function, that is, confusion, delirium, mental retardation, and dementia. Speech and language functions are seldom lost in these conditions but are deranged as part of a general impairment of perceptual and intellectual functions (see Chap. 21). Common to this category are certain special disorders of speech, such as mutism as outlined by Geschwind in his article on the “non-aphasic disorders of speech” (1964) and extreme perseveration (palilalia and echolalia), in which the patient repeats, parrot-like, sounds, words, and phrases. The odd constructs of language and other disorders of verbal communication of schizophrenics and some autistic individuals, extending to the production of meaningless phrases, neologisms, or jargon, are probably best included in this category as well but they derive from a disorder of thought.
3. A defect in articulation with intact mental functions, and comprehension of spoken and written language and normal syntax (grammatical construction of sentences). This is a pure motor disorder of the muscles of articulation and may be a result of flaccid or spastic paralysis, rigidity, repetitive spasms (stuttering), or ataxia. The terms dysarthria and anarthria are applied to this category of speech disorder.
4. An alteration or loss of voice because of a disorder of the larynx or its innervation—aphonia or dysphonia. Articulation and language are unaffected.
Chapter 27 fully considers the important but separable category of developmental disorders of speech and language.
The conventional teaching, based on correlations between various disorders of language and damage to particular areas of the brain, postulates four main language areas, situated in most persons in the left cerebral hemisphere (Fig. 22-1). The entire language zone that encompasses these areas is perisylvian, that is, it borders the sylvian fissure. Two language areas are receptive and two are executive, that is, the latter are concerned with the production (output) of language. The main receptive area, subserving the perception of spoken and probably of internal language, occupies the posterosuperior temporal area (the posterior portion of area 22) and Heschl gyri (areas 41 and 42). The posterior part of area 22 in the planum temporale is referred to as Wernicke area. A second receptive area occupies the angular gyrus (area 39) in the inferior parietal lobule, anterior to the visual receptive areas. The supramarginal gyrus, which lies between these auditory and visual language “centers,” and the inferior temporal region, just anterior to the visual association cortex, are probably part of the language apparatus as well. Here are located the integrative centers for cross-modal visual and auditory language functions.
The main executive, or output, region, situated at the posterior end of the inferior frontal convolution (Brodmann areas 44 and 45), is referred to as Broca area and is concerned with motor aspects of speech. Of note, this area is immediately adjacent to the facial motor area of the precentral gyrus. In some models of language, visually perceived words are given expression in writing through a fourth language area, the so-called Exner writing area in the posterior part of the second frontal convolution. However, this latter concept is controversial in view of the fact that widely separated parts of the language zone may cause a disproportionate disorder of writing. In any case, there are two parallel systems for understanding the spoken word and producing speech, and for the understanding of the written word and producing writing. They develop separately but are the integral components of the propositional, or semantic, system.