The Roles and Interplay of Reinforcement-Based and Error-Based Processes on Exploratory Behaviour in Parkinson’s Disease and Neurologically Intact Populations


Exploration is important when attempting to relearn motor skills following neurological disorders. Converging neuroanatomical evidence shows bidirectional connections between reinforcement-based (basal ganglia) and error-based (cerebellum) neural circuitries. However, it is unknown whether these bidirectional neural connections would influence exploratory behaviour. Here we designed two experiments and a computational model to investigate the unique and interacting roles of reinforcement and error feedback on motor exploration. Participants grasped the handle of a robotic manipulandum. They made reaching movements to a large target that promoted exploratory behaviour, without vision of their hand. Participants received either reinforcement feedback (pleasant sound, monetary gain for a success) and/or error feedback (small cursor showing hand position) at the end of their reach. We computed trial-by-trial statistical random walks (lag-1 autocorrelations) to quantify exploration. Aligned with model predictions, in Experiment 1 we found that neurologically intact individuals displayed significantly greater exploration with reinforcement feedback compared to error feedback (p < 0.001). Participants displayed moderate levels of exploration when receiving both forms of feedback, which was greater than isolated error feedback (p = 0.035) and less than isolated reinforcement feedback (p < 0.001). In Experiment 2, we considered those with Parkinson’s disease, who have compromised reinforcement-based neural circuits. Individuals with Parkinson’s had less exploration with reinforcement feedback compared to healthy age-matched controls (p < 0.001). Taken together, our results and model suggest that reinforcement-based and error-based processes respectively boost and suppress exploration, while in concert these processes oppose one another to result in moderate exploratory behaviour.