Developmental dyscalculia is assumed to be caused by a difference in brain function, and/or structure, in areas of the brain involved in mathematics. But what are these differences, and how much evidence is there for them?
This research is very much in its infancy compared to the research on dyslexia, because very little was known about how the brain represents mathematics until the last 15 or so years.
To date, most of the research has been in special populations associated with dyscalculia such as individuals with Turner's syndrome, Foetal Alcohol Syndrome, or born with a low birth weight [1-3]. All of these studies show either less grey matter (brain cells), or less brain activity in a specific area of the brain known to process mathematics (the intra-parietal sulcus).
Research on children with dyscalculia which is not due to a known medical syndrome is starting to emerge, with the same sort of findings. A recent brain imaging study showed less brain activity in parietal and frontal areas of the brain associated with mathematical cognition [4]. In addition children with dyscalculia also show difficulties on basic cognitive tasks known to involve these areas [5].
Research on acquired dyscalculia (dyscalculia acquired as a result of brain injury) fits with these findings; damage to the parietal lobes of the brain results in similar symptoms to developmental dyscalculia.
I thought the brain couldn't be changed?
This is a common misconception which is completely untrue. Every time you learn a new piece of information or a new skill, your brain changes. If you practice a new skill considerably your brain can show quite large changes. We call this ability to change "plasticity". The brain is at its most plastic during childhood, but it shows much plasticity in adulthood as well.
So even though dyscalculia is related to brain function, there is no reason why that function cannot be changed. It could be changed by experiences in the home (an environment which encourages attention to number), by teaching in school, and by intervention programmes.
Intervention programmes show particular promise for severe learning disabilities. We know from research on dyslexia that auditory training programs can result in significant improvement in reading which is associated with changes in brain function [6, 7].
But what is the root cause?
Why is the brain functioning differently in dyscalculic individuals? There are many possible causes, including both genetic and environmental, and an interaction of the two. The cause for one individual may not be the same as for another, and in many cases it may not be obvious.
Genetic causes include known genetic disorders such as Turner's syndrome, Fragile X syndrome, Velocardiofacial syndrome, Williams syndrome. In addition studies suggest that there are genes present in the general population which increase the risk of dyscalculia [8, 9].
Known environmental causes include alcohol consumption during pregnancy, and pre-term birth. Both of these can result in underdevelopment of the brain.
Dyscalculia often co-occurs with other learning difficulties such as dyslexia, dyspraxia, attention deficit and hyperactivity disorder (ADHD), and specific language impairment (SLI). This is probably because both environmental and genetic factors which affect brain development are likely to act on several areas of the brain at once.
References
[1] N. Molko, A. Cachia, D. Riviere, J. F. Mangin, M. Bruandet, D. Le Bihan, L. Cohen, and S. Dehaene, "Functional and structural alterations of the intraparietal sulcus in a developmental dyscalculia of genetic origin," Neuron, vol. 40, pp. 847-58, 2003.
[2] E. B. Isaacs, C. J. Edmonds, A. Lucas, and D. G. Gadian, "Calculation difficulties in children of very low birthweight: a neural correlate," Brain, vol. 124, pp. 1701-7, 2001.
[3] K. Kopera-Frye, S. Dehaene, and A. P. Streissguth, "Impairments of number processing induced by prenatal alcohol exposure," Neuropsychologia, vol. 34, pp. 1187-1196, 1996.
[4] K. Kucian, T. Loenneker, T. Dietrich, M. Dosch, E. Martin, and M. von Aster, "Impaired neural networks for approximate calculation in dyscalculic children: a functional MRI study.," Behavioral and Brain Functions, vol. 2, pp. 31, 2006.
[5] K. Landerl, A. Bevan, and B. Butterworth, "Developmental dyscalculia and basic numerical capacities: a study of 8-9-year-old students," Cognition, vol. 93, pp. 99-125, 2004.
[6] M. M. Merzenich, W. M. Jenkins, P. Johnston, C. Schreiner, S. L. Miller, and P. Tallal, "Temporal Processing Deficits of Language-Learning Impaired Children Ameliorated by Training," Science, vol. 271, pp. 77-81, 1996.
[7] E. Temple, G. K. Deutsch, R. A. Poldrack, S. L. Miller, P. Tallal, M. M. Merzenich, and J. D. Gabrieli, "Neural deficits in children with dyslexia ameliorated by behavioral remediation: evidence from functional MRI," Proc Natl Acad Sci U S A, vol. 100, pp. 2860-5., 2003.
[8] M. Alarcon, J. C. DeFries, J. G. Light, and B. F. Pennington, "A Twin Study of Mathematics Disability," Journal of learning disabilities, vol. 30, pp. 617-623, 1997.
[9] R. S. Shalev, O. Manor, B. Kerem, M. Ayali, N. Badichi, Y. Friedlander, and V. Gross-Tsur, "Developmental Dyscalculia Is a Familial Learning Disability," Journal of Learning Disabilities, vol. 34, pp. 59-65, 2001.
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