ASIMBOLIA. – From the Greek à privative and οὐμβόλον, symbol, representative sign; the temporary or definitive disappearance of groups of memories or representative images resulting from the destruction or functional blockage of specific cortical areas (v. LOCALIZZAZIONI CEREBRALI), hence the inability to recognize external objects or to perform particular practical activities.
To understand the mechanism and significance of such a disorder, it should be recalled that the identification of external objects, in the meaning and practical value they gradually acquire in our experience, is possible through the reference and associative links between the present sensation, which is always partial and more or less fragmentary, and the mnemonic traces acquired and deposited in specific cortical areas by previous sensations of similar objects. These traces, representative images of the objective value of external objects, constitute the “symbols,” specific in relation to the sensations from which they arose and therefore distinguished as visual, auditory, tactile, etc. Our practical activities too (movements, actions, language) are linked to “ideomotor symbols,” capable of eliciting and coordinating the complex neuromuscular functioning of the peripheral apparatuses of relational life (v. RELAZIONE). The word “agnosia” (ἀ priv., and γνῶσις, knowledge) is commonly used as a synonym for a.; some authors, however, reserve the former term exclusively for disorders of primary identification, properly conceptual, resulting from a failure of multisensory identification (A. Ceconi, p. 44).
Various forms of a. may be distinguished in relation to the various categories of images that are lacking: psychic deafness, whereby the patient does not understand the representative value of sounds and words; psychic blindness, in which, although able to see, the individual does not recognize persons, things, or graphic signs; motor and sensory aphasia (v. AFASIA), among 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 cannot mentally formulate its plan; ideomotor apraxia, in which, although the mental plan of the movement exists, it cannot be executed because of the loss of the necessary muscular images; agraphia, a particular form of apraxia limited to writing activity; astereognosis, the inability to recognize an object by touch because of the loss of geometric images of tactile and muscular origin; astereognosis combined with psychic blindness gives rise to Wernicke’s picture of total a. (Heil-Bronner’s asymbolic dementia or complete agnosia), in which it becomes impossible to grasp the meaning and practical value of any object.
Knowledge of a. and of its various forms is necessary for anyone who comes into contact with patients affected by apoplexy or presenting forms of mental alienation; indeed, in certain cases it may be difficult to distinguish a demented person from an apraxic patient or one with sensory aphasia. On the other hand, while a patient affected by motor aphasia, owing to a lesion of the extended a. area of Broca and in the left frontal lobe, cannot express himself in words, he retains the possibility of making himself understood through gestures because his intelligence is preserved; conversely, if the aphasia is sensory, he is incapable even of understanding spoken or written language because he is affected by psychic blindness and psychic deafness; it therefore becomes impossible to establish a conceptual relationship with him.