Asimbolia

ASIMBOLIA. - From the Greek à privative and σύμβολον, symbol, representative sign; the temporary or permanent disappearance of groups of memories or of representative images that follows upon the destruction or functional blocking of certain cortical zones (v. LOCALIZZAZIONI CEREBRALI), whence the impossibility of recognizing external objects or of expressing particular practical activities.

To understand the mechanism and the significance of such a disturbance, it must be recalled how the identification of external objects, in the meaning and practical value they have gradually assumed in our experience, is possible through the reference and associative links between the present sensation, always partial and more or less fragmentary, and the mnemonic traces acquired, deposited in certain cortical zones by previous sensations of similar objects. Such traces, representative images of the objective value of external objects, constitute the "symbols," specific in relation to the sensations from which they took their origin and therefore distinguished as visual, auditory, tactile, etc. Our practical activities too (movements, actions, language) are bound to "ideo-motor symbols," capable of arousing and coordinating the complex neuro-muscular interplay of the peripheral apparatuses of the life of relation (v. VITA VEGETATIVA E DI RELAZIONE). Commonly the word "agnosia" (ἀ priv., and γνῶσις, knowledge) is used as a synonym of a.; some authors, however, reserve the former exclusively for the disturbances of primary and properly conceptual identification, the fruit of a failed plurisensory identification (A. Ceconi, p. 44).

Various forms of a. may be distinguished in relation to the various categories of images that come to be lacking: psychic deafness, whereby the patient does not understand the representative value of sounds and words; psychic blindness, in which, though seeing, the individual does not recognize persons, things, graphic signs; motor and sensory aphasia (v. AFASIA), one of the most characteristic forms of a.; amusia, a particular form of aphasia limited to singing; ideational apraxia, when the patient is unable to perform the act because he is incapable of mentally formulating its plan; ideomotor apraxia, in which, though the mental plan of the movement exists, it cannot be executed owing to the loss of the necessary muscular images; agraphia, a particular form of apraxia limited to the activity of writing; astereognosia, the impossibility of recognizing an object by touch owing to the loss of the geometric images of tactile and muscular origin; astereognosia combined with psychic blindness gives rise to the picture of Wernicke's total a. (asymbolic dementia of Heil-Bronner, or complete agnosia), whereby it becomes impossible to grasp the meaning and practical value of any object whatsoever.

Knowledge of a. and of its various forms is necessary for anyone who comes into contact with patients struck by apoplexy or who present forms of mental alienation; indeed, in certain cases it may prove difficult to distinguish a demented patient from an apraxic or a sensory aphasic one. On the other hand, while a patient struck by motor aphasia, through lesion of the extensive area of Broca and in the left frontal lobe, cannot express himself in words, there remains for him the possibility of making himself understood by gestures because his intelligence is preserved; on the contrary, if the aphasia is sensory, he is incapable even of understanding the spoken or written word because he is affected by psychic blindness and psychic deafness; it therefore becomes impossible to enter into a conceptual relationship with him.

Giuseppe de Nino