In Fig. 183, the connections of the individual speech-centres are represented schem atically in horizontal section. The course of the tracts from one hemisphere to the other, through the corpus callosum, is to be noted.
On Fig. 182, we may trace the following paths : Speech comprehension : a a B; Repeating words : al Spontaneous speech : ml Reading : or B; Reading aloud : or Spontaneous writing : B A or A' Copying : of o 0 H h" ; Dictated writing : a' a A or 0 H hl At the same time, the diagram explains the different types of the disturbances of speech or aphasia.
A lesion of the speech-centre, M, leads to cortical motor aphasia. The patient can neither speak spontaneously, nor repeat; moreover, since reading and writing depend upon the integrity of the sensory as well as of the motor speech-centre, reading, spon taneous writing and dictated writing are also impaired. On the other hand, the patient understands what is spoken, since A is intact, and can copy writing.
A lesion of the sensory speech-centre, A, leads to cortical sensory aphasia. In the first place, comprehension of speech is lost; further, repetition, reading and dictation writing are suspended, while spontaneous writing and copying, as well as speech, are retained. In speaking, however, the patient manifests the symptoms of paraphasia, that is, the interpolation of incorrect words and exchange and mutilation of words.
Destruction of both chief centres, the motor and the sensory, leads to total aphasia.
When the efferent path from the motor speech-centre, M, is interrupted by a sub cortical effusion, the clinical picture of subcortical motor aphasia or word-dumbness appears; when the lesion involves the path to the sensory speech-centre, subcortical sen sory aphasia follows. These subcortical aphasiac leave inward speech intact, and the ability to read and write are retained. On the other hand, in subcortical motor aphasia, voluntary speech, repeating and reading aloud, are suspended or involved; in subcortical sensory aphasia, speech-comprehension, repeating and dictation writing are wanting or impaired.
If the path from the idea-centre to the motor speech-centre (BM) be interrupted, the patient is said to be affected with transcortical motor aphasia, with loss of voluntary speech and writing; if the path from the sensory centre to the idea-centre be broken, the resulting condition is termed transcortical sensory aphasia, with loss of the compre hension of speech and of writing.
An interruption of the path uniting the sensory and motor speech-centres (AM) leads to the so-called conduction aphasia. The ability of repeating words is impaired ; speech and comprehension of writing and the ability to copy are retained, as well as spontaneous speech and writing; the performance of these functions, however, is attended with the manifestations of paraphasia and paragraphic.