Note Acalculia: Acquired Anarithmetia'

Acalculia is a descriptive term used originally by Henschen (1920) to designate an acquired disorder of calculating ability. He specified that acalculia resulted from focal damage to the brain and collected all the cases of computational disorder which fulfilled these requirements available in the medical literature to that date. From this survey Henschen concluded that a distinct and independent cortical network existed for arithmetic functioning and therefore acalculia could exist as an entirely independent finding of brain damage or could be coupled with other symptomatology. No cases of "pure" acalculia are recorded and even case reports in which computation defect is the major or outstanding feature are uncom­ mon (Lewandowsky and Stadelman, 1908; Singer and Low, 1933; Lind­ quist, 1935; Cohn, 1961; Benson and Denckla, 1969). Most often, calcu­ lation defect is mentioned as one of several behavioral symptoms. This has led some investigators to classify acalculia by the signs and symptoms which accompany it or by the suspected site(s) of pathology. While the literature shows the usual variation in such classifications (Berger, 1926; Goldstein, 1948; Grewel, 1952; Critchley, 1953; Isham, 1970) there appears to be a basic agreement. If one excludes, by definition, calculating defects based on low intelligence or developmental problems, the following classification may be offered as a composite (after Hecaen, 1962): 1. Aphasic acalculia (figure or number alexia) An inability to handle numbers as words produces the calculation errors. 2. Visuo-spatial acalculia (either unilateral neglect or mispositioning of figures) An inability to align problems or to maintain place holding values produces computational errors. 3. Anarithmetia (true loss of computational ability) An inability to retrieve learned arithmetic values and/or manipulate these values.