Developmental dyscalculia.

Developmental dyscalculia (DD) is a learning disorder affecting the acquisition of school level arithmetic skills present in approximately 3-6% of the population. At the behavioral level DD is characterized by poor retrieval of arithmetic facts from memory, the use of immature calculation procedures and counting strategies, and the atypical representation and processing of numerical magnitude. At the neural level emerging evidence suggests DD is associated with atypical structure and function in brain regions associated with the representation of numerical magnitude. The current state of knowledge points to a core deficit in numerical magnitude representation in DD, but further work is required to elucidate causal mechanisms underlying the disorder.