The posterior Cerebellum is involved in constructing Social Action Sequences: An fMRI Study

Social neuroscience largely ignored the role of the cerebellum, despite its implications in a broad range of tasks and neurological disorders related to social functioning and inferences on others' mental state such as beliefs. One hypothesis states that during human evolution, the cerebellum's function evolved from a mere coordinator of fluent sequences of motions and actions, to an interpreter of action sequences without overt movements that are important for social understanding. The present study introduces new tasks to investigate the role of the cerebellum in sequencing, in which participants generated the correct chronological order of new or well-known event stories with or without social elements during functional neuroimaging (fMRI). Results showed strong cerebellar activation during order generation for all event types compared to passive viewing or reading events. More importantly, new social events involving true or false beliefs showed stronger activation in the bilateral posterior cerebellum (Crus 1 and Crus 2) compared to routine social and non-social (mechanical) events. This confirms the critical role of the posterior cerebellum in the understanding and construction of the correct order of action sequences relevant for social understanding. The present tasks and results may facilitate diagnoses and treatments of cerebellar dysfunctions in the future.