tDCS-induced hemispheric asymmetry alters belief updating
Nikki Marinsek1, Michael B. Miller1; 1University of California, Santa Barbara
Studies on various patient groups suggest that reasoning has a hemispheric asymmetry component. Previously, we proposed that neural networks in left frontal areas are driven toward increasing and maintaining certainty, while right frontal areas prioritize cohesion between beliefs and evidence. To test our proposal, we aimed to induce (or amplify) hemispheric asymmetry in healthy participants as they completed a probabilistic inference task. In the task, participants guessed which one of two possible U.S. states was selected based on the ethnicities of sequentially-presented residents from the selected state. Participants used a digital slider to indicate their beliefs and chose when to stop collecting evidence. Participants (N=21) completed the reasoning task before and during 20 minutes of 2mA High-Definition transcranial Direct Current Stimulation (HD-tDCS) in three separate sessions: a left hemisphere bias (LHbias) session, in which the anode was placed over the left inferior frontal gyrus (IFG; BA45) and the cathode over the right IFG, a right hemisphere bias (RHbias) session, in which the anode was placed over the right IFG and the cathode over the left IFG, and a sham session. As predicted, participants collected less evidence under LHbias stimulation than RHbias stimulation (t=-3.48,p<0.01) and became more certain in their beliefs early on during LHbias stimulation compared to RHbias stimulation (t=2.56,p<0.01). However, there were no significant differences in the Bayesian posterior estimates of the final observations, suggesting that LHbias stimulation drove participants to become certain more quickly, but did not change participants' level of certainty needed to make a final decision.
Topic Area: THINKING: Decision making