Cross-cortical implementation of spatial-numerical associations revealed by transcranial direct current stimulation and near-infrared-spectroscopy

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Fronto-parietal networks are critically involved in numerical cognition in general and spatial-numerical associations in specific. The modulation of numerical processing by transcranial direct current stimulation (tDCS) over different cortical regions provides insights into their shared and distinct neurocognitive causal networks. Previous stimulation studies were apparently specific to cathodal tDCS of the left prefrontal cortex (PFC) for modulation spatial-numerical associations, but regional specificity was not clear. The present project systematically disentangles effects of different electrode configurations and varies both target and return electrode positions to obtain regional specificity. WP1 will investigate the causal contributions of different network sites involved in numerical magnitude (distance effect) and spatial-numerical processing (SNARC effect) in magnitude comparison tasks, and contrast these effects to response inhibition functions (control task). In WP2, imaging of cortical hemodynamic activity with near-infrared spectroscopy (NIRS) concurrent to tDCS can enlighten the immediate physiological effects of tDCS interactions with spatial-numerical associations. The hemodynamic measurements are anticipated to demonstrate cross-cortical responses to prefrontal tDCS in posterior parietal cortex due to the fronto-parietal numerical processing network. Results corroborate the neuronal implementation of numerical magnitude processing and spatial-numerical associations in humans, and basic principles of tDCS effects in numerical cognition.