Effect of bilateral transcranial direct current stimulation on learning under uncertainty

This thesis investigates the role of the dorsolateral prefrontal cortex (DLPFC) in learning and decision-making under uncertainty. Using a two-armed bandit task with manipulations of expected uncertainty and neuromodulatory stimulation via transcranial direct current stimulation (tDCS), the study explores how lateralized DLPFC activation impacts probabilistic learning. Participants were randomly assigned to one of three stimulation groups - Right Anodal/Left Cathodal (RALC), Left Anodal/Right Cathodal (LARC), or sham - and completed a probabilistic task under high and low uncertainty conditions. The research found a significant main effect of uncertainty on accuracy, but there are no significant differences between tDCS groups or interactions. While theoretical models predict dissociable roles of the right and left DLPFC in adaptive behavior, the results suggest that tDCS may not reliably modulate decision-making efficiency in this context. These findings underscore the complexity of neuromodulation effects and highlight the need for further studies to disentangle task-specific, individual, and methodological factors. The thesis contributes to the growing literature on neural mechanisms of uncertainty processing and the potential - and limitations - of brain stimulation as a cognitive enhancement tool.