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The DLPFC is thought to be critically involved in maintaining attention away from behaviourally irrelevant information, and in the establishment of attentional control settings. These play an important role in the phenomenon of top-down bias to features in the visual field – also known as attentional bias. This paper probes the involvement of the left DLPFC in attentional bias by manipulating its cortical excitability via tDCS and then analysing these effects following an induced attentional bias towards the colour green. Although both anodal and cathodal tDCS over the left DLPFC decrease distractibility caused by biased but irrelevant objects, further interrogation of our data reveals theoretically differential mechanisms for each type of stimulation. Anodal tDCS appears to increase cognitive control over attentional bias-related items that are behaviourally irrelevant, allowing for their efficient disregard. In contrast, cathodal tDCS appears to lessen the overall effect of the induced attentional bias, potentially by reducing the influence of top-down modulated attentional control settings thus preventing the implementation of the control setting favouring green items. These results suggest a potential causal role of the left DLPFC in the cognitive mechanism underlying attentional bias. • tDCS over left DLPFC decreases distractions caused by biased but irrelevant objects. • Anodal tDCS likely increases cognitive control over irrelevant attentional bias-related items. • Cathodal tDCS likely reduces the influence of top-down attentional control settings. • These results suggest a potential causal role of the left DLPFC in mechanisms underlying attentional bias. [ABSTRACT FROM AUTHOR]