Reduction of implicit cognitive bias with cathodal tDCS to the left prefrontal cortex.

Implicit associations can interfere with cognitive operations and behavioral decisions without direct intention. Enhancement of neural activity with anodal transcranial direct current stimulation (tDCS) was proposed to reduce implicit associations by means of improved cognitive control. However, a targeted reduction of distractive implicit associations by inhibitory cathodal tDCS, recently shown in spatial-numerical associations, provides an interesting alternative approach to support goal-directed behavior with transcranial brain stimulation. To test this rationale with a sham-controlled cross-over design, a standardized Implicit Association Test (IAT) was performed by 24 healthy participants parallel to 1 mA cathodal or sham tDCS to the left prefrontal cortex. In this double-classification task, insect versus flower pictures and negative versus positive words are mapped together onto two shared response keys with crossed response assignments in separate blocks. Responses were faster when insect + negative and flower + positive stimuli required the same answer (IAT effect). Most critically, the IAT effect was reduced during cathodal tDCS as compared to sham stimulation. Thus, results are consistent with the proposed stimulation rationale, with previous observations, and complementary to previous studies using different tDCS configurations.