Acalculia

Acalculia
Classification and external resources
ICD-10	F81.2 and R48.8
ICD-9-CM	784.69
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Acalculia is an acquired impairment in which patients have difficulty performing simple mathematical tasks, such as adding, subtracting, multiplying and even simply stating which of two numbers is larger. Acalculia is distinguished from dyscalculia in that acalculia is acquired late in life due to neurological injury such as stroke, while dyscalculia is a specific developmental disorder first observed during the acquisition of mathematical knowledge. The name comes from the Greek "a" meaning "not" and Latin "calculare", which means "to count".

The term "acalculia" was coined by Henschen in 1925; it refers to the decrease in cognitive capacity for calculation that results from damage to the brain. Earlier, in 1908, researchers Lewandowsky and Stadelmann published the first report of an individual afflicted with calculation impairment due to brain damage. The individual had trouble performing calculations on paper and mentally. Further, he had difficulty recognizing arithmetic symbols. The report was key in that it established calculation disorders as separate from language disorders, as the two were formerly associated. Henshcen's research was consistent with Lewandowsky's and Stadelmann's finding. From his research, he was also able to propose that certain areas of the brain played particular roles involved in the understanding and execution of calculation. These areas include the third frontal convolution (pronunciation of numbers), the angular gyrus and the fissure interparietalis (reading of numbers), and the angular gyrus again for the writing of numbers. Shortly after Henshen's advances, Berger in 1926 distinguished between primary and secondary acalculia. Primary acalculia is a "pure" condition in which an individual can neither comprehend mathematical concepts nor perform mathematical operations. Secondary acalculia is a loss of calculation abilities that stems from other cognitive difficulties, such as memory. It has been questioned whether primary acalculia can exist independently of other cognitive impairments. In 1936, Lindquist proposed that lesions of different areas of the brain can cause different calculation defects, and that there are therefore several variations of acalculia. In 1940, Gerstmann claimed that acalculia is associated with aspects of Gerstmann's syndrome, which include right-left confusion, agraphia, and digital agnosia. In 1983, Boller and Grafman further concluded that calculation difficulties can also arise from various shortcomings, such as the inability to assign value to the name of a number. Little research has been done on acalculia, despite the fact the calculation is considered an essential, upper-level cognitive skill. However, calculation skills are assessed in neuropsychological exams such as the Mini-Mental State Examination (MMSE). There exist no norms for Acalculia against which a person can be compared to assess his/her level of cognitive impairment with regards to calculation abilities.

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