Neural Signatures of Reward and Sensory Prediction Error in Motor Learning

Two distinct processes contribute to changes in motor commands during reach adaptation: reward based learning and sensory error based learning. In sensory error based learning, the mapping between sensory targets and motor commands is recalibrated according to sensory error feedback. In reward based learning, motor commands are associated with subjective value, such that successful actions are reinforced. We recorded EEG from humans to identify and dissociate the neural correlates of reward prediction error (RPE) and sensory prediction error (SPE) during learning tasks designed to isolate each response. We designed a visuomotor rotation task to isolate sensory error based learning in response to SPE, which was induced by altered visual feedback of hand position. In a reward learning task, we isolated learning in response to RPE induced by binary reward feedback that was decoupled from the visual target. We found that a fronto-central event related potential called the feedback related negativity (FRN) occurred specifically in response to RPE during reward based learning. A more posterior component called the P300 was evoked by feedback in both tasks. In the visuomotor rotation task, P300 amplitude was increased by SPE and was correlated with learning rate, while in the reward learning task P300 amplitude was increased by reward relative to non reward and by surprise regardless of feedback valence. We suggest that the FRN specifically marks RPE while the P300 reflects more general processing of prediction error.