Reward and expectancy effects on neural signals of motor preparation and execution

The magnitude and prospect of rewards can have strong modulatory effects on response preparation and execution. Importantly, reward-seeking behavior in real life happens under an environment characterized by uncertainty and dynamic changes. The current study investigated how the brain's motor and cognitive control system adapts to the dynamic changes in the environment in pursuit of rewards. To this end, we tested the effect of reward and expectancy on the hallmark neural signals that reflect activity in motor and prefrontal systems, the lateralized readiness potential (LRP) and the mediofrontal (mPFC) theta oscillations, while participants performed an expected and unexpected actions to retrieve rewards. To better capture the dynamic changes in neural processes represented in the LRP waveform, we decomposed the LRP into the preparation (LRP_prep) and execution (LRP_exec) components. In the comparison of LRP magnitude across task conditions, we found a greater LRP_prep when large rewards were more likely, reflecting a greater motor preparation to obtain larger rewards. We also found a greater LRP_exec when large rewards were presented unexpectedly, suggesting a greater motor effort placed for executing a correct movement when presented with large rewards. In the analysis of mPFC theta, we found a greater theta power prior to performing an unexpected than expected response, indicating its contribution in response conflict resolution. Collectively, these results demonstrate an optimized motor and cognitive control to maximize rewards under the dynamic changes of real-life environment.