InXuence of galvanic vestibular stimulation on egocentric and object-based mental transformations

The vestibular system analyses angular and linear accelerations of the head that are important information for perceiving the location of one’s own body in space. Vestibular stimulation and in particular galvanic vestibular stimulation (GVS) that allow a systematic modiWcation of vestibular signals has so far mainly been used to investigate vestibular inXuence on sensori-motor integration in eye movements and postural control. Comparatively, only a few behavioural and imaging studies have investigated how cognition of space and body may depend on vestibular processing. This study was designed to diVerentiate the inXuence of left versus right anodal GVS compared to sham stimulation on object-based versus egocentric mental transformations. While GVS was applied, subjects made leftright judgments about pictures of a plant or a human body presented at diVerent orientations in the roll plane. All subjects reported illusory sensations of body self-motion and/ or visual Weld motion during GVS. Response times in the mental transformation task were increased during right but not left anodal GVS for the more diYcult stimuli and the larger angles of rotation. Post-hoc analyses suggested that the interfering eVect of right anodal GVS was only present in subjects who reported having imagined turning themselves to solve the mental transformation task (egocentric transformation) as compared to those subjects having imagined turning the picture in space (object-based mental transformation). We suggest that this eVect relies on shared functional and cortical mechanisms in the posterior parietal cortex associated with both right anodal GVS and mental imagery.