The effect of oppositional parietal transcranial direct current stimulation on lateralized brain functions

<jats:title>Abstract</jats:title><jats:p>Cognitive functions such as numerical processing and spatial attention show varying degrees of lateralization. Transcranial direct current stimulation (<jats:styled-content style="fixed-case">tDCS</jats:styled-content>) can be used to investigate how modulating cortical excitability affects performance of these tasks. This study investigated the effect of bi‐parietal <jats:styled-content style="fixed-case">tDCS</jats:styled-content> on numerical processing, spatial and sustained attention. It was hypothesized that <jats:styled-content style="fixed-case">tDCS</jats:styled-content> would have distinct effects on these tasks because of varying lateralization (numerical processing left, spatial attention right) and that these effects are partly mediated by modulation of sustained attention. A single‐blinded, crossover, sham‐controlled study was performed. Eighteen healthy right‐handed participants performed cognitive tasks during three sessions of oppositional parietal <jats:styled-content style="fixed-case">tDCS</jats:styled-content> stimulation: sham; right anodal with left cathodal (<jats:styled-content style="fixed-case">RA</jats:styled-content>/<jats:styled-content style="fixed-case">LC</jats:styled-content>); and right cathodal with left anodal (<jats:styled-content style="fixed-case">RC</jats:styled-content>/<jats:styled-content style="fixed-case">LA</jats:styled-content>). Participants performed a number comparison task, a modified Posner task, a choice reaction task (<jats:styled-content style="fixed-case">CRT</jats:styled-content>) and the rapid visual processing task (<jats:styled-content style="fixed-case">RVP</jats:styled-content>). <jats:styled-content style="fixed-case">RA</jats:styled-content>/<jats:styled-content style="fixed-case">LC tDCS</jats:styled-content> impaired number comparison performance compared with sham, with slower responses to numerically close numbers pairs. <jats:styled-content style="fixed-case">RA</jats:styled-content>/<jats:styled-content style="fixed-case">LC</jats:styled-content> and <jats:styled-content style="fixed-case">RC</jats:styled-content>/<jats:styled-content style="fixed-case">LA tDCS</jats:styled-content> had distinct effects on <jats:styled-content style="fixed-case">CRT</jats:styled-content> performance, specifically affecting vigilance level during the final block of the task. No effect of stimulation on the Posner task or <jats:styled-content style="fixed-case">RVP</jats:styled-content> was found. It was demonstrated that oppositional parietal <jats:styled-content style="fixed-case">tDCS</jats:styled-content> affected both numerical performance and vigilance level in a polarity‐dependent manner. The effect of <jats:styled-content style="fixed-case">tDCS</jats:styled-content> on numerical processing may partly be due to attentional effects. The behavioural effects of <jats:styled-content style="fixed-case">tDCS</jats:styled-content> were specifically observed under high task demands, demonstrating the consequences of an interaction between stimulation type and cognitive load.</jats:p>