Neural mechanisms for discounting head-roll-induced retinal motion.

An extensive series of physiological studies in macaques shows the existence of neurons in three multisensory cortical regions, dorsal medial superior temporal area (MSTd), ventral intraparietal area (VIP), and visual posterior sylvian area (VPS), that are tuned for direction of self-motion in both visual and vestibular modalities. Some neurons have congruent direction preferences, suggesting integration of signals for optimum encoding of self-motion trajectory; others have opposite preferences and could be used for discounting retinal motion that arises from perceptually irrelevant head motion. Whether such a system exists in humans is unknown. Here, artificial vestibular stimulation was administered to human participants during fMRI scanning in conjunction with carefully calibrated visual stimulation that emulated either congruent or opposite stimulation conditions. Direction and speed varied sinusoidally, such that the two conditions contained identical vestibular stimulation and identical retinal stimulation, differing only in the relative phase of the two components. In human MST and putative VIP, multivoxel pattern analysis permitted classification of stimulus phase based on fMRI time-series data, consistent with the existence of separate neuron populations responsive to congruent and opposite cue combinations. Decoding was also possible in the vicinity of parieto-insular vestibular cortex, possibly in a homolog of macaque VPS.