Right Middle Occipital Gyrus is Associated with Egocentric Spatial Orientation During Body Tilt: Evidence from a Repetitive Transcranial Magnetic Stimulation Study

Accurate perception of the orientation of external objects relative to the body, known as egocentric spatial orientation, is fundamental to performing action. Previously, we found via behavioural and magnetic resonance imaging voxel-based morphometry studies that egocentric spatial orientation is strongly distorted when the whole body is tilted with respect to gravity, and that the magnitude of this perceptual distortion is correlated with the grey matter volume of the right middle occipital gyrus (rMOG). In the present study, we further validated the association between the neural processing in the rMOG and the perceptual distortion by transiently suppressing neural activity in this region using low-frequency repetitive transcranial magnetic stimulation (rTMS) and evaluating the consequent effect on perceptual distortion. Our results showed that rTMS over the rMOG significantly reduced perceptual distortions when the body was tilted in the frontal plane, while it did not affect egocentric spatial orientation in the upright position. No significant changes in perceptual distortion were observed when rTMS was applied to another cortical candidate (the right temporo-parietal junction). These results provide evidence that neural processing in the rMOG is associated with body tilt-related perceptual distortion, suggesting that the rMOG may be engaged in egocentric spatial orientation related to gravitational information.