Neural mechanisms of volitional problem solving

Complex problems often allow multiple paths to a solution. Choosing and taking the best path is thus an important part of the executive cognition that underpins intelligent problem-solving behaviour. However, once a path is chosen, the motor system must be activated for executing it. This interface between problem-solving and voluntary action has rarely been studied. We recorded EEG movement-related potentials while participants performed the classic “Tower of London” problem-solving task. In a control condition, participants merely followed instructed steps without planning for any goal, and thus without any sense that their movements solved a problem. EEG readiness potential (RPs) preceding each action were stronger for problem-solving than for instructed conditions, confirming previous studies. Further, the RP was significantly increased prior to the first move of multi-move solutions compared to later moves, demonstrating an EEG correlate of goal-directed planning. We further used multivariate pattern analysis (MVPA) to distinguish self-generated from instructed actions. Classifier performance broadly tracked the dynamics of the readiness potential, improving over a 1s period before action, but dropped sharply in the final 200 ms before movement, consistent with a shift from premotor preparation into execution processes. Importantly, classifier performance was better for the first move of multi-step sequences than for later moves, confirming that our MVPA detected planning of solutions, rather than implementation of individual steps in a solution. Taken together, these results show a deep interaction between executive function and volition, and draw attention to the fact that, if a problem can be solved, the solution inevitably requires executive cognition to trigger voluntary action, based on a plan.