Acalculia is an acquired impairment in which people 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". Signs and symptoms Calculation impairments include the inability to perform simple mathematical operations, such as addition, subtraction, division, and multiplication. As calculation involves the integration of several cognitive skills, it is understood that an individual with acalculia (or calculation difficulties) is deficient in any of the following four realms: 1) understanding that every number represents a value and immediately registering this value, 2) recognizing a number's value with respect to other numbers, 3) knowing a number's location in series of numbers, and 4) association of a numerical symbol with its name, spoken verbally. Young schoolchildren are presented with mathematical concepts in a cumulative manner. Advancement requires the grasping of fundamental concepts before progressing to more difficult and involved concepts. There is a natural variation in the speed with which young schoolchildren grasp mathematical concepts, and those that have extreme difficulty retaining the foundations of mathematical concepts (such as global quantification or numerosity perception) are considered to have developmental dyscalculia. Variations Acalculia is associated with lesions of the parietal lobe (especially the angular gyrus) and the frontal lobe and can be an early sign of dementia. Acalculia is sometimes observed as a "pure" deficit, but is commonly observed as one of a constellation of symptoms, including agraphia, finger agnosia and right-left confusion, after damage to the left angular gyrus, known as Gerstmann's syndrome. Studies of patients with lesions to the parietal lobe have demonstrated that lesions to the angular gyrus tend to lead to greater impairments in memorized mathematical facts, such as multiplication tables, with relatively unimpaired subtraction abilities. Conversely, patients with lesions in the region of the intraparietal sulcus tend to have greater deficits in subtraction, with preserved multiplication abilities. These double dissociations lend support to the idea that different regions of the parietal cortex are involved in different aspects of numerical processing. Cause Damage to the left angular gyrus is known to cause computational difficulties like those associated with