In daily life, the trade-off between exploration of alternative opportunities and exploitation of the benefits of the choice at hand is encountered often. While the ability of mammals to switch to explorative courses of action has been extensively studied in machine learning and ethology fields, much less attention in neuroscience has been given to understanding how the brain mediates such decisions in humans. To date, no mechanism has been put forward. The proposed project seeks to understand how communication among neural regions gives rise to switches to explorative behavior, or decisions to take alternative choices about which the reward probabilities are uncertain, during a learning task. The project will use transcranial direct current stimulation to test specific hypotheses about the interactions among cortical regions and their effects on exploratory behavior. Behavior will be modeled using a Bayesian learning algorithm and neural activity before and after stimulation will be measured using functional magnetic resonance imaging. The mechanistic relationships among neural regions and behavior will be examined using dynamic causal modeling , a technique that was developed at the host institution. The results of the project will sketch out a mechanistic model of explorative decision making at the neural systems level. Understanding how brain regions causally interact during exploration will narrow a critical gap in basic neuroscientific knowledge of exploration and exploit. Our approach may also have direct applications to clinical neurology. The temporary inhibition of frontal regions could serve to simulate neuropathological insults resulting in deficits in task switching and stereotyped behaviors. Knowledge gained by studying this model system may then be applied in the development of novel therapeutic strategies.