Excitatory cerebellar transcranial direct current stimulation boosts the leverage of prior knowledge for predicting social events

Accumulating evidence suggests that the cerebellum plays a crucial role for social processing, by generating internal models of social events based on statistical learning of behavioral regularities. It is unclear, however, whether the cerebellum is only involved in forming or also in retrieving and updating internal models for the prediction of forthcoming actions. Here, we used cerebellar transcranial Direct Current Stimulation (ctDCS) to modulate the performance of healthy adults in an action prediction task. First, in an implicit-learning phase, the probability of co-occurrence between actions and contextual elements was manipulated to form either strongly or moderately informative expectations. Then, ctDCS was delivered in a testing phase assessing how these expectations affected the ability to predict ambiguous (temporally occluded) actions. Results showed that anodic, compared to sham, ctDCS boosted the prediction of actions embedded in moderately, but not strongly, informative contexts. The occurrence of the effect when delivering ctDCS exclusively during the testing phase, thus after expectations were established, suggests that the cerebellum is involved in the retrieval and updating, and not only learning, of internal models. This encourages the exploration of restorative effects of ctDCS in patients with social perception deficits related to poor use of predictive internal models.