Role of the cerebellum in time perception: a TMS study in normal subjects.

The aim of this study was to investigate the role of the cerebellum in a temporal-discrimination task without movement production in healthy subjects. Ten healthy subjects underwent a time-perception task with somatosensory stimuli. Two pairs of electrical stimuli: the first considered the reference pair (rp) with a standard interval of 400 ms and the second, the test pair (tp), with variable intervals ranging from 300 to 500 ms, were applied by surface electrodes on the right forearm. Subjects were instructed to compare time intervals of rp and tp and to estimate whether the tp interval was shorter than, equal to, or longer than that of rp. The task was performed in baseline and after 1 Hz rTMS over the right and left cerebellar hemisphere. The right cerebellar rTMS worsened temporal discrimination of cutaneous somatosensory electrical stimuli on the ipsilateral hand. rTMS of the left cerebellar hemisphere did not determine significant changes in the subjects' performance with respect to the baseline. These findings suggest that the cerebellum plays a role in merely perceptive aspects of temporal information processing.