What is Developmental Dyscalculia?

Mathematics is one of the main challenges faced by students throughout school life, with a long-lasting impact on social life, including employability and income. The development of research on numerical cognition occurs with the study of mathematics learning in specific developmental dyscalculia (DD) and its related deficiencies. The literature on DD has been researched at two levels. First, thoughts about the nosological state of the disorder and its diagnosis. The other is the main research findings on the cognitive foundations of DD, from numerical representations to general domain processes including working memory and language.

What is Developmental Dyscalculia?

Developmental dyscalculia is a specific learning disorder that affects the normal acquisition of arithmetic skills. Genetic, neurobiological and epidemiological evidence indicates that dyscalculia, like other learning difficulties, is a brain-based disorder. However, poor teaching and environmental deprivation also play a role in its etiology. Since the neural network of both hemispheres includes the lower tier of normal arithmetic skills, dyscalculia may result from dysfunction of both hemispheres, but the left parietotemporal area is of particular importance. The prevalence of developmental dyscalculia in the school-age population is 5 to 6% and is common in girls as well as boys. Dyscalculia can occur prematurely and as a result of low birth weight. In addition, it is frequently encountered in various neurological disorders such as attention deficit hyperactivity disorder (ADHD), developmental language disorder, epilepsy, and fragile X syndrome.

Developmental dyscalculia has proven to be a permanent learning disability in about half of the sixteen affected children, at least in the short term. Educational interventions range from memorizing arithmetic facts to developing strategies for solving arithmetic exercises. Although the role of improving long-term prognosis and outcomes has not yet been established, developmental dyscalculia has proven to be a permanent learning disability, at least in the short term, in about half of the sixteen affected children.

Living in today’s society requires well-developed mathematical competences. As cliché as this statement sounds, there is a solid scientific literature showing that higher mathematical competencies are associated with higher employability and income, profitable financial decisions, and even better health outcomes. Despite this long-standing evidence, many adults and children, even from developed countries, find it difficult to do simple arithmetic.

The reasons for failing in mathematics are diverse and are based on socioeconomic, educational, and emotional factors. Mathematics is a complex and abstract discipline, mostly dependent on formal teaching at school. Moreover, mathematical knowledge is also largely cumulative, so newer, more complex and abstract concepts depend on previous knowledge that can be acquired intuitively or formally at school, such as reading the order of number words. Therefore, a large part of the difficulties children face in learning or performing math activities is due to the complexity of math. Compared to other disciplines, it is known that difficulty in learning mathematics is seen in children in the early years of school.

Yet some children present persistent and significant difficulties in learning mathematics that cannot be explained by socioeconomic, emotional, educational, psychiatric or intellectual factors. In these cases, the label developmental dyscalculia (DD) is often applied, the difficulties cover a wide range of mathematical tasks such as reading and writing numbers in different formats, comparing numbers and quantities, and performing basic arithmetic operations. Some researchers also note shortcomings in the ability to understand and use symbolic codes to represent magnitude and numerical information. Estimates for the prevalence of DD range from 3 to 6% of school-age children. Despite the relative consensus on what the difficulties characterize DD, there is still some controversy regarding diagnostic criteria, neuropsychological bases, and rehabilitation strategies.

Comorbidity and Cognitive Heterogeneity

Investigation of developmental dyscalculia (DD) nosology also includes examining its comorbidities with other syndromes and how the cognitive profile changes between individuals. It is estimated that only 30% of children with DD lack comorbidities. Its main comorbidities are developmental dyslexia and ADHD, with 40% for the first and 25 to 42% for the second. According to Rubinsten and Henik, different cognitive deficits can be the cause of difficulties in learning mathematics, and comorbidities often result from a combination of deficiencies. For example, cases that lack mathematical knowledge (where the DD label is applied) are due to a lack of abstract representation of the number at the cognitive level and a deficiency in the functioning of the intraparietal sulcus at the neural level.

The comorbidity of dyscalculia and ADHD is explained by the co-occurrence of deficiencies in number processing and attention mechanisms. In contrast, the disease concomitant with dyslexia is due to a single deficiency in the angular gyrus that will cause a deficiency in associating symbols (numbers, words) with a meaning. Comorbid conditions are called math learning difficulties (MLD).

As a result, although the study of the cognitive basis of numerical representations and mathematical performance is relatively new, there is evidence in understanding the development of mathematical abilities. In addition, a coherent body of scientific evidence has already gathered that has allowed significant advances in identifying and correcting mathematical challenges. However, this is a broad field of study and there are still a few open questions. Currently, longitudinal studies and replication studies are particularly important.