Root of dyscalculia found

Mar 22 2007

Scientists led by UCL (University College London) have induced dyscalculia in subjects without the maths learning difficulty for the first time. The study, which finds that the right parietal lobe is responsible for dyscalculia, potentially has implications for diagnosis and management through remedial teaching.

Dyscalculia is just as prevalent in the population as dyslexia and attention deficit hyperactivity disorder - around 5% of the population is affected. However, dyscalculia has not been given the same attention as other disorders and the underlying brain dysfunction causing dyscalculia is still a mystery. It is hoped that this study will provide a better understanding of the condition and lead to better diagnosis and treatment.

Dr Roi Cohen Kadosh, of the UCL Institute of Cognitive Neuroscience, said: "This is the first causal demonstration that the parietal lobe is the key to understanding developmental dyscalculia. Most people process numbers very easily - almost automatically - but people with dyscalculia do not. We wanted to find out what would happen when the areas relevant to maths learning in the right parietal lobes were effectively knocked out for several hundred milliseconds. We found that stimulation to this brain region during a maths test radically impacted on the subjects' reaction time.

"This provides strong evidence that dyscalculia is caused by malformations in the right parietal lobe and provides sold grounds for further study on the physical abnormalities present in dyscalculics' brains. It's an important step to the ultimate goal of early diagnosis through analysis of neural tissue, which in turn will lead to earlier treatments and more effective remedial teaching."

Using neuronavigated transcranial magnetic stimulation (TMS) to stimulate the brain, scientists were able to bring about dyscalculia in normal subjects for a short time while the subjects completed a maths task that involved comparing two digits, one larger in physical size than the other and the other larger numerically. For example, the subjects compared a 2 and a 4. The 2 was in a larger font than the 4 and subjects had to decide which digit was numerically larger.

The effect of TMS lasted only a few hundred milliseconds in the subjects and was brought on just at the point when the subject had to evaluate the numbers and decide which had the greater value or which was physically bigger. The test was designed to measure the subjects' automatic processing of numbers and was rolled out to both people with the dysfunction and those without it.

The researchers found that non-dyscalculic participants displayed dyscalculic-like behaviour in number processing only during TMS-induced neuronal activity disruptions to the right intraparietal sulcus. These findings were further validated by testing participants suffering from developmental dyscalculia. The results of the dyscalculic group reproduced the behavioural results obtained in non-dyscalculic volunteers during right parietal TMS, but not after left parietal TMS or sham stimulation.

This novel approach of directly comparing healthy participants with TMS-induced virtual dyscalculia to participants suffering from developmental dyscalculia enabled the researchers to propose a direct causal relationship between malfunctions along the right intraparietal sulcus and developmental dyscalculia.