National audienceWe introduces a new hypothesis concerning the dissociated role of the basal ganglia in the selection and the evaluation of action that has been formulated using a theoretical model and confirmed experimentally in monkeys. To do so, and prior to learning, we inactivated the internal part of the Globus Pallidus (GPi, the main output structure of the BG) with injections of Muscimol and we tested monkeys on a variant of a two-armed bandit task where two stimuli are associated with two distinct reward probabilities (0.25 and 0.75 respectively). Unsurprisingly, performance in such condition are at the chance level since the output of basal ganglia cannot influence behaviour. However, the theoretical model predicts that in the meantime, values of the stimuli are nonetheless covertly evaluated and learned. This has been tested and confirmed on the next day, when inhibition has been removed: monkeys instantly showed significant improved performances (above chance level), hence demonstrating they have learned and knew the relative value of the two stimuli. This tends to suggest that the critic part of the basal ganglia may be utilized for evaluating different actors whose origin are yet to be determined experimentally
