Abstract
In healthy individuals, increasing cognitive load induces an asymmetric deployment of visuospatial attention, which favors the right visual space. To date, the neural mechanisms of this left/right attentional asymmetry are poorly understood. The aim of the present study was thus to investigate whether a left/right asymmetry under high cognitive load is due to a shift in the interhemispheric balance between the left and right posterior parietal cortices (PPCs), favoring the left PPC. To this end, healthy participants completed a visuospatial attention detection task under low and high cognitive load, whilst undergoing biparietal transcranial direct current stimulation (tDCS). Three different tDCS conditions were applied in a within-subjects design: sham, anodal left/cathodal right, and cathodal left/anodal right stimulation. The results revealed a left/right attentional asymmetry under high cognitive load in the sham condition. This asymmetry disappeared during cathodal left/anodal right tDCS, yet was not influenced by anodal left/cathodal right tDCS. There were no left/right asymmetries under low cognitive load in any of the conditions. Overall, these findings demonstrate that attentional asymmetries under high cognitive load can be modulated in a polarity-specific fashion by means of tDCS. They thus support the assumption that load-related asymmetries in visuospatial attention are influenced by interhemispheric balance mechanisms between the left and right PPCs.
Highlights
The spatial allocation of visual attention can be affected by non-spatial attentional aspects, such as cognitive load
We hypothesized that further shifting the interhemispheric balance in favor of the left posterior parietal cortices (PPCs) would exacerbate the rightward attentional shift under high cognitive load
We aimed to investigate the neural substrates of the rightward attentional shift observed under high cognitive load in healthy subjects, by directly modulating the interhemispheric interactions between the PPCs with biparietal transcranial direct current stimulation (tDCS)
Summary
The spatial allocation of visual attention can be affected by non-spatial attentional aspects, such as cognitive load. For instance in dual task paradigms (e.g., concurrently completing a non-spatial and a spatial attentional task), healthy individuals show a rightward shift in visuospatial attentional deployment (Pérez et al, 2009; Naert et al, 2018). This rightward shift may be influenced by the effect of cognitive load on the interhemispheric balance between the dorsal networks directing visual attention in space (Kinsbourne, 1993; Corbetta and Shulman, 2011). The reversed montage (inhibitory cathode over the left PPC, and excitatory anode over the right PPC; referred to as CL/AR) would contribute to restore interhemispheric balance, thereby reducing the rightward attentional shift under high cognitive load
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