This chapter discusses heterogeneous aspects of developmental dyscalculia (DD) in terms of behaviour, cognitive operations, and neural structures. It has been suggested that DD is an isolated learning deficiency, involves a domain-specific deficit (in the capacity to enumerate), and a specific neural deficiency (in the intraparietal sulcus). We present findings that (1) DD involves both domain-specific and domain-general abilities; (2) in many cases behaviours, as well as cognition in those with DD are characterized by deficits in other areas, such as attention or memory and not only as a number sense deficiency; and (3) studies of the neural structures involved in DD reveal areas and mechanisms that hint toward heterogeneous damage. We suggest that similar to other learning disabilities, heterogeneity is the rule, rather than an exception. Accordingly, in order to reach a comprehensive understanding of DD, studies should aim at unravelling the basis for this heterogeneity.
