Aphasia

APHASIA', a term used to denote various defects in the com prehension and expression of both spoken and written language which result from lesions of the brain. Aphasic disorders may be classed in two groups : first, receptive or sensory aphasia, which comprises (a) inability to understand spoken language (auditory aphasia), and (b) inability to read (visual aphasia, or alexia) ; second, emissive or motor aphasia, under which category are in cluded (a) inability to speak (motor vocal aphasia, or aphemia), and (b) inability to write (motor graphic aphasia, or agraphia). It has been shewn that each of these defects is produced by destruc tion of a special region of the cortex of the brain, in right-handed people, situated in the left cerebral hemisphere ; this is the reason why aphasia is so commonly associated with paralysis of the right side of the body.

Auditory Aphasia.

The auditory speech centre is situated in the posterior part of the first and second temporo-sphenoidal con volutions on the left side of the brain. Hearing is unimpaired but spoken language is quite unintelligible.

Visual Aphasia or Alexia.

The visual speech centre, which is located in the left angular gyrus, is connected with the two centres for vision which are situated one in either occipital lobe. The individual is not blind, he sees the words and letters perfectly, but they appear to him as unintelligible cyphers. When the visual speech centre is destroyed, the memories of the visual images of words are obliterated and interference with writing results. On the other hand, when the lesion is situated deeply in the occipital lobe, and does not implicate the cortex, but merely cuts off the con nections of the angular gyrus with both visual centres, agraphia is not produced, for the visual word centre and its connection with the graphic centre are still intact.

Motor Vocal Aphasia or Aphemia.

The centre for motor vocal speech is situated in the posterior part of the third left frontal convolution and extends on to the foot of the left ascend ing frontal convolution (Broca's convolution). Complete destruc tion of this region produces loss of speech, although of ten a few words, such as "yes" and "no," and, it may be, emotional exclama tions such as "Oh, dear!" are retained. In most cases of motor vocal aphasia there is associated agraphia, which is perhaps to be explained by the proximity of the graphic centre. When the lesion is situated below the cortex of Broca's convolution but de stroys the fibres which pass from it towards the internal capsule, agraphia is not produced.

Agraphia.

Those who favour the separate existence of a graphic centre locate it in the second left frontal convolution. It may be, however, that the anatomical relationship between the graphic centre and that for the fine movement of the hand is so close that a lesion in this situation which produces agraphia must at the same time cause a paralysis of the hand.

The speech centres are all supplied by the left middle cerebral artery. When this artery is blocked close to its origin by an em bolus or thrombus, total aphasia results. It may be, however, that only one of the smaller branches of the artery is obstructed, and, according to the region of the brain to which this branch is distrib uted, one or more of the speech centres may be destroyed. Occlu sion of the left posterior cerebral artery causes extensive softening of the occipital lobe and produces visual aphasia. Further, a tumour, abscess, haemorrhage or meningitis may be so situated as to damage or destroy the individual speech centres or their con necting commissures. The amount of recovery to be expected in any given case depends upon the nature, situation and extent of the lesion, and upon the age of the patient. Even of ter complete destruction of the speech centres, perfect recovery may take place, for the centres in the right hemisphere of the brain are capable of education. This is only possible in young individuals. In the great majority of instances the nature of the lesion is such as to render futile all treatment directed towards its removal.

Bulletin de la Societe anatomique (1861) ; Wernicke, Der Aphasische Symptomen-complex (Breslau, 1874) ; Kuss maul, Ziemssen's Cyclopaedia, vol. xiv. p. 759; Wyllie, The Disorders of Speech (1895) ; Elder, Aphasia and the Cerebral Speech Mechanism (1897) ; Collins, The Faculty of Speech (1897) ; Byrom Bramwell, "Will-making and Aphasia," British Medical Journal (1897) ; Bastian, Aphasia and other Speech Defects (1898) ; "The Morison Lectures on Aphasia," The Lancet (1906). See also the works of Charcot, Hugh lings Jackson, Dejerine, Lichtheim, Pitres, Grasset, Ross, Broadbent, Mills, Bateman, Mirallie, Exner, Marie and others.