CNS 2018: tDCS-induced hemispheric asymmetry alters belief updating

This year at the Cognitive Neuroscience Society conference we're presenting our first set of high-definition transcranial Direct Current Stimulation (HD-tDCS) results.

We used tDCS to temporarily alter neural activity in participants' left and right frontal lobes in order to test our predictions about hemispheric asymmetry in reasoning. We applied 2mA of anodal stimulation to the inferior frontal gyrus of one hemisphere and 2mA of cathodal stimulation to the inferior frontal gyrus of the opposite hemisphere to temporarily bias neural activity toward the left (LH-bias stimulation) or right (RH-bias stimulation) hemisphere. Participants completed a probabilistic guessing task while receiving LH-bias, RH-bias, or sham stimulation.

We found that, as predicted, LH-bias stimulation was associated with more certain guesses early on in each trial. However, there was no effect on the amount of evidence collected or the evidence threshold set for deciding to stop evidence collection. Contrary to our predictions, RH-bias stimulation was not associated with greater "backtracks" in beliefs following conflicting evidence. It's possible that this task did not induce salient conflicts between beliefs and evidence since the stimuli were abstract and inconsequential. To see if RH-bias stimulation affects belief updating under more meaningful belief-evidence conflicts, we are currently running a new tDCS experiment that uses more realistic and emotionally-salient stimuli.