The disturbances of gesture and expression in the insane have hitherto been treated almost invariably in a descriptive manner-the present paper is an attempt to classify them on a scientific basis. As a preliminary measure the author seeks to establish the existence of a veritable “function of expression “-with anatomically differentiated centres and paths of conduction. In this connection, however, a distinction must be made between voluntary movements of expression and those which are involuntary or automatic. The first, e.g., the gestures which an orator uses to lend additional force to his words-result from imitation and practice, and to explain them we need not postulate any other centres than those which preside over all voluntary movements. As regards the second, however, e.g., laughter, the facial expressions of fear, grief, disgust, and other emotions-the case is altogether different. This second group consists of instinctive movements-almost invariably the same for a given emotion-movements which the will cannot even prevent-and which are accompanied by vasomotor and other purely reflex phenomena. This function of emotional expression is of primitive origin -it precedes language both ontogcnctically and philogcnetically-and long before the speech centres are in action it has established an independent existence. Many of its manifestations exist at birth, and some even arc found in anencephalic monsters. There is no question here of education-an innate organisation is implied. We arc thus led to the conception of a nervous apparatus of expression having no direct relation to the cerebral centres for voluntary movement. This conception is confirmed by various anatomical and clinical facts. Bell, Romoerg, and others have described cases of voluntary paralysis unaccompanied by paralysis of expression; e.g., a patient is incapable of voluntarily contracting the muscles of the face, while emotional expression is perfectly preserved. Pick and Rosenbach describe cases of the converse type-absence of emotional expression, with preservation of voluntary movement. Nothnagel, on the basis of several post mortem examinations, stated that if the optic thalamus and the thalamic radiation were intact, emotional expression would be preserved, whatever might be the case as regards volitional movement. This proposition was confirmed by Bechtcrcw's experiments on animals. We may conclude, therefore, (i) that distinct nervous mechanisms exist for voluntary movement and the movements of emotional expression, (a) that the optic thalami and their connections arc the co-ordinating centres for the various muscle groups concerned in the expression of affective states. The fundamental difference existing between voluntary and involuntary expression is well seen if the one is substituted for the other. The man who laughs with his psychical centres differs absolutely from the man who laughs with his thalamus. The first strives consciously for the result, the second simply submits to the automatism of his lower centres. To be able to practically distinguish these two modes is the whole art of detecting the simulator.
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