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Effective connectivity
of the multiplication network:
A functional MRI and multivariate Granger causality mapping study

Frank Krueger,
Cognitive Neuroscience Section, NINDS, NIH
and Center for the Study of Neuroeconomics, Krasnow Institute, GMU

Developmental neuropsychology and functional neuroimaging evidence indicates that simple and complex mental calculation is subserved by a fronto-parietal network. However, effective connectivity in form of connection direction and strength among regions within the fronto-parietal network is still unexplored. By combining event-related functional MRI and multivariate Granger Causality Mapping (GCM), we administered a multiplication verification task to healthy participants asking them to solve single and double-digit multiplications. The goals of our study were first, to identify the effective connectivity of the multiplication network and second, to compare the effective connectivity patterns between a low and a high arithmetical competence group. The manipulation of multiplication difficulty revealed a fronto-parietal network encompassing the bilateral intraparietal sulcus (IPS), left pre-supplementary motor area (PreSMA), left precentral gyrus (PreCG), and right dorsolateral prefrontal cortex (DLPFC). The multiplication network was driven by an intraparietal IPS-IPS circuit hosting a representation of numerical quantity intertwined with a fronto-parietal DLPFC-IPS circuit engaged in temporary storage and updating of arithmetic operations. Both circuits received additional inputs from the PreCG and PreSMA playing more of a supportive role in the mental calculation process. Importantly, the low competence group based its calculation more on a feedback driven fronto-parietal DLPFC-IPS circuit, whereas the high competence group based its calculation more on a feedback driven intraparietal IPS-IPS circuit. This study provides first evidence that multivariate GCM is a sensitive approach to investigate effective connectivity of mental processes involved in mental calculation and to compare group level performances for different populations.

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