ASIMBOLIA. — From Gk. privative *a-* and *symbolon*, representative sign; temporary or permanent disappearance of groups of representative memories or images that follows destruction or functional blockage of certain cortical areas (v. LOCALIZZAZIONI CEREBRALI), resulting in the inability to recognize external objects or to express particular practical activities.
To understand the mechanism and significance of such a disturbance, it must 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 current sensation—always partial and more or less fragmentary—and the mnemonic traces acquired and stored in certain cortical areas from 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 thus distinguished into visual, auditory, tactile, etc. Even our practical activities (movements, actions, language) are linked to “ideo-motor symbols,” capable of evoking and coordinating the complex neuro-muscular interplay of the peripheral apparatus of relational life (v. RELIAZIONE).
The term “agnosia” (from Gk. privative *a-* and *gnōsis*, knowledge) is commonly used as a synonym for *a.*; some authors, however, reserve the former exclusively for disturbances of primary and properly conceptual identification arising from a failure of multi-sensory identification (A. Ceconi, p. 44).
Various forms of *a.* can be distinguished in relation to the different categories of images that are lost: psychic deafness, in which the patient does not understand the representative value of sounds and words; psychic blindness, in which, despite being able to see, the individual does not recognize people, things, or 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 an act because incapable of mentally formulating the plan; ideo-motor apraxia, in which, although the mental plan for the movement exists, it cannot be executed due to the loss of the necessary muscular images; agraphia, a particular form of apraxia limited to writing; astereognosis, the inability to recognize an object by touch due to the loss of geometric images of tactile and muscular origin; astereognosis combined with psychic blindness gives rise to the picture of Wernicke’s total *a.* (Heil-Bronner’s asemantic dementia or complete agnosia), in which it becomes impossible to grasp the meaning and practical value of any object.
Knowledge of *a.* and its various forms is necessary for those who come into contact with patients suffering from apraxia or who present forms of mental alienation; indeed, in certain cases it may be difficult to distinguish a demented patient from an apraxic or a sensory aphasic. On the other hand, while a patient suffering from motor aphasia, due to a lesion in the “extended Broca area” in the left frontal lobe, cannot express himself in words, he retains the ability to make himself understood through gestures because his intelligence is preserved; conversely, if the aphasia is sensory, he is also unable to understand spoken or written language because affected by psychic blindness and psychic deafness, making it impossible to establish any conceptual rapport with him.