Role of the right middle occipital gyrus in egocentric spatial orientation in reference to gravitational information: Evidence from a pre-registered rTMS study

Accurate perception of the orientation of external objects relative to the body, known as egocentric spatial orientation, is fundamental to action. Previously, we found via behavioral and magnetic resonance imaging voxel-based morphometry studies that egocentric spatial orientation is distorted when the whole body is tilted with respect to gravity, and that the magnitude of this perceptual distortion is correlated with grey matter volume in the right middle occipital gyrus (rMOG). In the present pre-registered study, we demonstrated that neural processing in the rMOG is indeed a cause of the perceptual distortion. We transiently suppressed neural activity in the rMOG by applying low-frequency repetitive transcranial magnetic stimulation (rTMS) and evaluated the consequent effect on perceptual distortion. Our results showed that while rTMS over the rMOG significantly reduced perceptual distortion when the body was tilted with respect to gravity, it did not affect egocentric spatial orientation when in the upright position. No changes in perceptual distortion were observed when rTMS was applied to a control site (right temporoparietal junction) or to air (sham TMS). These results indicate that neural processing in the rMOG during body tilt is an essential cause of perceptual distortion, suggesting that the rMOG is engaged in egocentric spatial orientation concerning gravitational information. Significance statementThe findings of this pre-registered study support a causal role of neural activity in the right middle occipital gyrus (rMOG) in the perceptual distortion of egocentric spatial orientation induced by whole-body tilt relative to gravity. We suppressed neural activity in the rMOG using low-frequency repetitive transcranial magnetic stimulation (rTMS) and measured perceptual distortion. We observed a significant reduction in perceptual distortion after rTMS over the rMOG, but not after control or sham rTMS. These results provide, for the first time, direct evidence of the engagement of the rMOG in egocentric spatial orientation in reference to gravitational information.