For a minute there, I lost myself … dosage dependent increases in mind wandering via prefrontal tDCS

Allowing our mind's eye to wander to task unrelated thoughts can impact productivity and, in many everyday settings, safety. However, the drifting of our thoughts from our current task(s)/situation to others is undeniably a common occurrence and has even been associated with adaptive outcomes in terms of creativity. Previous researchers have used non-invasive transcranial direct current stimulation (tDCS), applied to the prefrontal cortex, to modulate mind wandering occurrences. However, little is known about the influence of varying stimulation parameters, such as polarity and intensity, on mind wandering, or even more broadly on executive function performance. Here, in a pre-registered design (n = 150), we investigated the effect of stimulation polarity and intensity on mind wandering while subjects undertook a repetitive cognitive task (sustained attention to response task, SART). We found a linear effect of stimulation dosage on the propensity to have task unrelated thoughts. Specifically, greater intensity cathodal tDCS resulted in increased mind wandering with anodal and cathodal stimulation showed the same pattern of results. These findings confirm a key role for the left prefrontal cortex in mind wandering, and, of import, demonstrate that increased dosage could lead to larger effects on mind wandering behaviours. This is in contrast to some previous reports suggesting that stimulation dosage presents a U-shaped function, highlighting the potential for optimal dosages to vary depending upon the targeted brain region and behaviour.