Cortial stimulation of the left angular gyrus transiently disrupts addition and multiplication: two case studies.
Ter Horst, A.T.
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Neuropsychological and neuroimaging studies strongly suggest engagement of the left angular gyrus (AG) in the efficient retrieval of verbal mathematical facts from memory. This retrieval is considered important in mental calculation taks that rely on mathematical facts, such as multiplication tables learned by heart and simple exact addition sums. Only few attempts have been made to perform corticostimulation on the AG to test this idea. The objective of this study was to infer whether temporarily disturbing the AG by corticostimulation disrupts simple exact addition and multiplication. We present two cases in which cortical stimulation of the AG transiently disrupts solving these type of sums. Stimulation of the superior parietal cortex and the occipital lobe did not reveal interference with addition and multiplication. These results are in line with the proposed function of the AG as important in calculation tasks that rely on the retrieval of mathematical facts. They also suggest the usefulness of cortical stimulation in elucidating the neural substrates of mental calculation.