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 cerebellum on visual dependency, quantified by the subjective visual vertical bias induced by rotating optokinetic stimulation (OKS). Electric field simulations in high-resolution head models were used to ensure focal stimulation of the cerebellum at the group level. The results demonstrated that repetitive transcranial magnetic stimulation (rTMS) applied to the cerebellar 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 judgement 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. Significance StatementThe cerebellum has been implicated in multisensory integration for spatial orientation, but its direct role in visuo-vestibular interactions remains limited. Using 1-Hz rTMS, we demonstrated that stimulation of the cerebellar vermis significantly reduced visual dependency in the perception of gravitational direction, as measured by the subjective visual vertical bias induced by rotating optokinetic stimulation. This effect was absent when adjacent areas, such as early visual cortex and the cerebellar hemisphere, were stimulated. These results suggest that the cerebellar vermis is directly involved in visuo-vestibular interaction, providing new insights into the cerebellar contribution to spatial orientation in humans.