Visuo-Vestibular Integration for Self-Motion: Human Cortical Area V6 Prefers Forward and Congruent Stimuli

BACKGROUNDThe integration of visual and vestibular input is crucial for self-motion. Information from both sensory systems merges early in the central nervous system. Among the numerous cortical areas involved in processing this information, some (V6 and VIP) respond specifically to vestibular anteroposterior information. OBJECTIVETo further understand the involvement of these and other areas in self-motion processing when vestibular and visual information are combined with varying congruence and direction parameters. METHODSFifteen subjects underwent an MRI session while receiving visual (optic flow patterns) and galvanic vestibular stimuli mimicking six conditions: (1) visual forward, (2) visual backward, visual forward with (3) congruent or (4) incongruent vestibular information, visual backward with (5) congruent or (6) incongruent vestibular information. RESULTSThe combination of concurrent vestibular stimulation and fully consistant optic flow patterns activated several bilateral cortical areas found predominantly in the insula. Among these vestibular areas and those previously defined in our initial study, the large majority do not show any specifity for the forward/backward direction or for the visuo-vestibular congruency. A notable exception was the parieto-occipital area V6, which showed a marked preference for congruent visuo-vestibular signals and for cues signaling forward motion. CONCLUSIONSBy showing that V6 is more active when visuo-vestibular signals are more ecological (i.e. when both signals specify the most common self-motion direction), our results support the view that this area plays a crucial role in visuo-vestibular integration during self-motion.