When brain stimulation backfires: the effects of prefrontal cortex stimulation on impulsivity.

Transcranial direct current stimulation (tDCS) can sometimes cause the opposite of its intended effect. These reverse effects may be related in part to individual differences in personality and neurochemistry. Previous studies have demonstrated that dopamine levels can impact the effects of tDCS. In the present study, 124 healthy participants took the UPPS impulsive behavior scale. Participants then underwent a single, randomized anodal or sham tDCS session on the prefrontal cortex. While the effects of tDCS were still active, they performed the Stop Signal Task, a measure of state impulsivity. tDCS was associated with increased errors on this task in people who had higher scores on the UPPS in two facets of impulsivity that correlate with dopamine levels. tDCS had no effects on people who are low in trait impulsivity. These results suggest that the reverse effects of tDCS could be associated with inter-individual differences in personality and neurochemistry.