The internal time keeper: Causal evidence for the role of the cerebellum in anticipating regular acoustic events

Most acoustic events in our environment do not appear randomly but are rather predictable due to the temporal regularity in that they occur. Besides sensory-related cortical areas, the cerebellum has been suggested as a key structure in temporal processing and in the anticipation of future events. Hence, patients with cerebellum lesions show impaired precision in temporal processing as reflected in the reduced ability to exploit temporal regularity. Using transcranial direct current stimulation (tDCS), we here aimed to draw further causal conclusions on the human cerebellum as functionally relevant in temporal processing of acoustic events. We focused on the electrophysiologic P3b, a large positive wave apparent in the electroencephalography (EEG), that represents encoding of task-relevant events and that has been demonstrated as sensitive to the exploitation of temporal regularities. Participants received 30 min of anodal, cathodal or sham tDCS over the cerebellum while they performed two oddball paradigms with different temporal regularities in that the acoustic stimuli were presented. Following clinical observations, we hypothesized that tDCS-effects will be present in the regular oddball paradigm only, thus, in the condition that allows anticipating the occurrence of subsequent stimuli. In result, we found that cathodal tDCS over the cerebellum reduced the P3b-amplitude specifically in response to target stimuli in the regular paradigm. Thereby, tDCS-induced changes mirror the effects of cerebellar lesions in clinical samples. Our data provides direct evidence for a causal link between the human cerebellum and auditory processing of temporal regularity and emphasize future work on a potential benefit of cerebellar-tDCS in clinical samples.