Abstract
Visuo-vestibular integration is crucial for locomotion, yet the cortical mechanisms involved remain poorly understood. We combined binaural monopolar galvanic vestibular stimulation (GVS) and functional magnetic resonance imaging (fMRI) to characterize the cortical networks activated during antero-posterior and lateral stimulations in humans. We focused on functional areas that selectively respond to egomotion-consistent optic flow patterns: the human middle temporal complex (hMT+), V6, the ventral intraparietal (VIP) area, the cingulate sulcus visual (CSv) area and the posterior insular cortex (PIC). Areas hMT+, CSv, and PIC were equivalently responsive during lateral and antero-posterior GVS while areas VIP and V6 were highly activated during antero-posterior GVS, but remained silent during lateral GVS. Using psychophysiological interaction (PPI) analyses, we confirmed that a cortical network including areas V6 and VIP is engaged during antero-posterior GVS. Our results suggest that V6 and VIP play a specific role in processing multisensory signals specific to locomotion during navigation.
Highlights
Self-motion perception permits us to estimate our on-going change of position within the surrounding space to properly interact with our environment
Our results demonstrate that the activations elicited by Lat galvanic stimulation (GVS) in areas V6, ventral intraparietal (VIP), cingulate sulcus visual (CSv), hMT+, and posterior insular cortex (PIC) are reliable across different stimulation parameters (a 1 Hz sinewave alternating between ±3 mA in Smith et al, 2012 vs. a 1 mA step in the present study)
A previous neuroimaging study employed the usual binaural bipolar mode, where the anode is placed on one mastoid process and the cathode on the other to identify visual cortical areas that receive vestibular inputs (Smith et al, 2012)
Summary
Self-motion (egomotion) perception permits us to estimate our on-going change of position within the surrounding space to properly interact with our environment. Egomotion is processed from multisensory inputs, vestibular and visual ones whose integration remains poorly understood (e.g., Britten, 2008). Several groups have shown vestibular projections in the medial superior temporal area (MST), a visual area involved in object-motion and self-motion perception based on optic flow (Duffy, 1998; Bremmer et al, 1999; Gu et al, 2006). MST projects towards the ventral intraparietal area (VIP) that is sensitive to visual heading and receives vestibular inputs (Klam and Graf, 2003a,b). Wall and Smith (2008) found that the ventral intraparietal (VIP) and the cingulate sulcus visual (CSv) areas had selective responses to optic flow patterns that are compatible with those received by our retina during locomotion
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