Neuropsychological Aspects of Developmental Dyscalculia

Abstract

The classification of arithmetic disorders has traditionally been predicated on neuropsychological features and associated learning disabilities. We assessed the compatibility of these classifications on a non-referred, population-based cohort of 139 children with developmental dyscalculia (DC). The assessment battery included reading and spelling tests, evaluation for attention deficit hyperactivity disorder (ADHD), Wechsler Intelligence Scale for Children-Revised (WISC-R), ReyOsterreith complex figure, Benton's test of facial recognition, ten-word learning test, word fluency, trail making, tapping sequence, and sequential hand movements. Arithmetic was assessed using an individually administered, standardised arithmetic battery. ADHD was assessed clinically and by questionnaires. The hypotheses tested in this study were (1) whether children with DC and disabilities in reading (R) and/or spelling (RS) had better arithmetic skills than children with DC only and (2) whether ADHD as a co-morbid diagnosis would significantly affect arithmetic function in children with DC. The first hypothesis was tested by dividing the 139 children with DC into two groups: those with DC and RS (DC+ RS, n = 35) and those with normal reading skills (DC, n = 104). The two groups were similar for socioeconomic status, gender, performance IQ, and proportion of children with ADHD. We found that on the arithmetic battery, the DC+RS group was more profoundly impaired on subtraction and division and their verbal IQ was significantly lower. No differences between the two groups were found on the other neuropsychological parameters. The second hypothesis was evaluated by dividing the children into three groups DC+ADHD (n = 28), DC+R (n = 17), and DC-only (n = 84). Similar demographic and neuropsychological characteristics were found among groups. On the arithmetic