Developmental dyscalculia: heterogeneity might not mean different mechanisms.

Research indicates that developmental dyscalculia (DD; a mathematical deficiency) involves a single brain area abnormality - in the intraparietal sulcus. This is surprising because, (i) the behavioural deficits are heterogeneous, (ii) multiple problems are most common in most cases (co-morbidity) and (iii) different aspects of intact number processing are represented in different brain areas. Hence, progress in the study of DD might be limited by conceptual issues. This work looks at biological and cognitive findings within DD and delineates frameworks for studying the neurocognitive basis of DD. We offer three alternative frameworks. These proposed frameworks have the potential of facilitating future discussions, work in the field and have implications for studies of similar disorders like dyslexia and attention-deficit/hyperactivity disorder.