To act or not to act: Learning the value of not acting

Sometimes the best course of action is to do nothing (non­action). However, it is unclear how the brain learns the value of non­action and how it is compared to the value of action during decision making. To address these questions, we repeatedly confronted human participants with the choice of selecting one alternative with a button press or the other by doing nothing. Analysis of the behavioural data with reinforcement learning models did not reveal differences between the rate at which participants learned the values of action and non­action. At feedback, in addition to brain activity correlated with the updated value of action and action prediction error, we found brain activities correlated with the updated value of non­action and non­action prediction error. The representations of non­action prediction error and non­action value were found in right and left inferior frontal gyri, respectively, which are regions previously implicated in studies of response inhibition. Additionally, we found value comparison activity at feedback in dorsomedial frontal cortex and frontopolar cortex, the latter predicting individual differences in exploitative behaviour and performance across participants. Our results suggest that the processes of learning the value of non­action resemble those for learning the value of action, engaging response inhibition regions in a manner analogous to the engagement of regions involved in the planning and implementing of action when learning the value of action.