Dyscalculia Overview

Dyscalculia is a specific learning disability in the area of math. Characteristics include a weakness in automatic retrieval of basic facts, and the use of less efficient problem solving strategies.  When adding two numbers they may use a count all method.  Counting up to the first number and then counting the second.  A more efficient strategy is a count minimum method which starts with the larger number and counts from there.  Numbers are seen as clusters of ones but not also as patterns of numbers.  Eight would be seen as eight ones but not necessarily two sets of four.
 
Processing numbers uses an Approximate Number System (ANS) located in the intraparietal sulcus. A characteristic of this ANS is a mental number line. Using this mental number line, the speed and ability of comparing two numbers depends upon the distance between the two numbers. It is easier to compare numbers that are further apart. It is easier to compare 3 with 8 that it is to compare 6 with 8. It is also a ratio comparison. The difference between 6 and 8 is 2, but it is easier to compare 6 and 8 than 24 and 26 which are also 2 apart. There are individual differences in the ability to compare numbers and this difference can predict math ability. This ability also improves with age all the way to adulthood. However differences in brain activation in the intraparietal sulcus have been shown for individuals with dyscalculia. Butterworth found a small region of reduced gray-matter density in the left IPS in adolescent dyscalculics. He also found a reduced probability of connections to other parts of the brain.
 
Fractions do not lend themselves to this integer processing system and can be difficult for many students. Even students that can add 1/3 and 1/4 and get 7/12 will say that 1/4 is larger than 1/3. Others will say the answer is 2/7. Part of the issue is that fractions are taught with these whole number concepts and these concepts are often misapplied. Matthews from the University of Wisconsin-Madison is researching a Ratio Processing System (RPS) located in the fronto-parietal section of the brain. Neurons in this area react to specific ratios regardless of the absolute value of the items. For example a set of neurons will react to a ratio such as 3/4 and less so for nearby ratios such as 5/8 and much less so for ratios such as 1/4. He found that increased sensitivity to these nonsymbolic ratio magnitudes was correlated with higher fraction and algebra ability. He also found that training symbolic to nonsysbolic links resulted in improved performance on math tasks.
 
Another area in the brain involved in mathematical processing was discovered by Josef Parvize at the Stanford University School of Medicine. He has identified an area of the brain that is activated when numbers are presented. This activation does not occur when the numbers are spelled out (one versus 1). The area of the brain involved is the inferior temporal gyrus an area generally known to be involved in the processing of visual information lending support for the concept that visual spatial processing is a factor in dyscalculia.