Cerebellum Involvement in Visuo-vestibular Interaction for the Perception of Gravitational Direction: A Repetitive Transcranial Magnetic Stimulation Study.

Accurate perception of the direction of gravity relies on the integration of multisensory information, particularly from the visual and vestibular systems, within the brain. Although a recent study of patients with cerebellar degeneration suggested a cerebellar role in visuo-vestibular interaction in the perception of gravitational direction, direct evidence remains limited. To address this gap, we conducted two experiments with 42 healthy participants to evaluate the impact of repetitive 1 Hz transcranial magnetic stimulation (rTMS) over the posterior cerebellar vermis on visual dependency, quantified by the subjective visual vertical bias induced by rotating optokinetic stimulation (OKS). Electric field simulations in high-resolution generic head models were used to ensure focal stimulation of the cerebellum at the group level. The results demonstrated that the rTMS applied to the vermis significantly attenuated the OKS-induced shift in visual vertical (SVV) bias. This effect was not observed when stimulation was applied to the early visual cortex (V1-2) or the cerebellar hemisphere. Also, the vermis rTMS had no effect on the judgment precision in the absence of visual motion cues, suggesting that the rTMS may reduce visual weight in visuo-vestibular processing by increasing visual motion noise rather than affecting vestibular function. These findings suggest a direct involvement of the cerebellar vermis in the visuo-vestibular interaction underlying the perception of gravitational direction, providing new insights into cerebellar contributions in human spatial orientation.