Half of what? Number bisection, line bisection, number line bisection and estimation differ in their hemodynamic...

Spatial and numerical processing are tightly connected capacities of human cognition. It is assumed that space and numbers draw on common neural networks. Here, we used functional near-infrared spectroscopy (fNIRS) during spatial-numerical bisection tasks to assess neural activity in a natural production paradigm. Thirty-six neurotypical participants used a touch pen during line bisection, number line bisection, number line estimation, number bisection, and an active neutral task (figure-copying). Accordingly, we systematically varied spatial and numerical requirements in a series of four bisection tasks and a neutral task, in an ecologically valid setting with comparable visuo-motor affordances (i.e., ticking a line vs. drawing a figure/number) that are compatible with fNIRS recordings. We had four main findings. (1) All employed bisection tasks showed comparable activation in the bilateral supramarginal gyrus and intraparietal sulcus. (2) Prefrontal activation in the bilateral inferior frontal gyrus was higher for tasks with greater numerical requirements (i.e., number line estimation and number bisection). (3) Relative to figure-copying, number bisection showed stronger deactivation in the left angular gyrus. However, planned contrasts between line bisection, number line bisection and number line estimation did not show different neural activity. (4) In connectivity analyses, number bisection showed a higher functional connectivity from the left intraparietal sulcus to the angular gyrus, compared to number line estimation. Overall, functional connectivity was higher in the left hemisphere. This study provides evidence that inferior frontal regions are engaged in more conceptual spatial-numerical processing in an ecologically valid experimental setting.