Transcranial direct current stimulation over left and right DLPFC: Lateralized effects on planning performance and related eye movements

• Initial thinking time (ITT) in the Tower of London reflects internalization and planning processes.
• Internalization and planning have been linked to left and right dlPFC, respectively.
• ITT is paradoxically facilitated after left cathodal/right anodal tDCS over dlPFC.
• Facilitation of ITT by tDCS is associated with shorter duration of planning proper.

Left and right dorsolateral prefrontal cortex (dlPFC) were recently found to be differentially affected by unilateral continuous theta-burst stimulation, reflected in an oppositional alteration of initial thinking time (ITT) in the Tower of London planning task.Here, we further explored this finding using bilateral transcranial direct current stimulation (tDCS) and simultaneous tracking of eye movements. Results revealed a decrease in ITT during concurrent cathodal tDCS of left dlPFC and anodal tDCS of right dlPFC. Eye-movement analyses showed that this facilitating tDCS effect was associated with the actual planning phase, thus reflecting a planning-specific impact of stimulation. For the reverse stimulation pattern of cathodal tDCS of right dlPFC and anodal tDCS of left dlPFC, an increase in gaze shifts was observed, without a significant impact on ITT.Taken together, these findings corroborate that enhanced planning performance can be obtained by boosting right dlPFC and dismantling the inhibitory impact of left dlPFC.