When dissimilar images are presented to the two eyes, binocular rivalry (BR) occurs, and perception alternates spontaneously between the images. Although neural correlates of the oscillating perception during BR have been found in multiple sites along the visual pathway, the source of BR dynamics is unclear. Psychophysical and modeling studies suggest that both low- and high-level cortical processes underlie BR dynamics. Previous neuroimaging studies have demonstrated the involvement of high-level regions by showing that frontal and parietal cortices responded time locked to spontaneous perceptual alternation in BR. However, a potential contribution of early visual areas to BR dynamics has been overlooked, because these areas also responded to the physical stimulus alternation mimicking BR. In the present study, instead of focusing on activity during perceptual switches, we highlighted brain activity during suppression periods to investigate a potential link between activity in human early visual areas and BR dynamics. We used a strong interocular suppression paradigm called continuous flash suppression to suppress and fluctuate the visibility of a probe stimulus and measured retinotopic responses to the onset of the invisible probe using functional MRI. There were ∼130-fold differences in the median suppression durations across 12 subjects. The individual differences in suppression durations could be predicted by the amplitudes of the retinotopic activity in extrastriate visual areas (V3 and V4v) evoked by the invisible probe. Weaker responses were associated with longer suppression durations. These results demonstrate that retinotopic representations in early visual areas play a role in the dynamics of perceptual alternations during BR.

Visually induced motion sickness (VIMS) is triggered in susceptible individuals by stationary viewing of moving visual scenes. VIMS is often preceded by an illusion of self-motion (vection) and/or by inappropriate optokinetic nystagmus (OKN) responses associated with increased activity in the human motion-sensitive middle temporal area (MT+). Neuroimaging studies have reported predominant right hemispheric activation in MT+ during both vection and OKN, suggesting that VIMS may result from desynchronization of activity between left and right MT+ cortices. However, this possibility has not been directly tested. To this end, we presented VIMS-free and VIMS-inducing movies in that order while measuring the temporal correlations between corresponding left and right visual cortices (including MT+) using functional magnetic resonance imaging. The inter-hemispheric correlation was reduced significantly during the viewing of the VIMS-inducing movie compared to the control VIMS-free movie in the MT+ of subjects reporting VIMS, but not in insusceptible subjects. In contrast, there were no significant inter-hemispheric differences within VIMS-free or VIMS-inducing movie exposure for visual area V1, V2, V3, V3A or V7. Our findings provide the first evidence for an association between asynchronous bilateral MT+ activation and VIMS. Desynchronization of left and right MT+ regions may reflect hemispheric asymmetry in the activities of functional networks involved in eye movement control, vection perception and/or postural control.

Movies depicting certain types of motion often provoke uncomfortable symptoms similar 2 to motion sickness, termed visually induced motion sickness (VIMS). VIMS generally 3 evolves slowly during the viewing of a motion stimulus and, when the stimulus is 4 removed, the recovery proceeds over time. Recent human neuroimaging studies have 5 provided new insights into the neural bases of the evolution of VIMS. In contrast, no 6 study has investigated the neural correlates of the recovery from VIMS. Study of the 7 recovery process is critical for the development of a way to promote recovery and could 8 provide further clues for understanding the mechanisms of VIMS. We thus investigated 9 brain activity during the recovery from VIMS with functional connectivity magnetic 10 resonance imaging. We found enhanced recovery-related functional connectivity patterns 11 involving brain areas such as the insular, cingulate, and visual cortical regions, which 12 have been suggested to play important roles in the emergence of VIMS. These regions 13 also constituted large interactive networks. Furthermore, the increase in functional 14 connectivity was correlated with the subjective awareness of recovery for the following 15 five pairs of brain regions: insula-superior temporal gyrus, claustrum-left and right 16 inferior parietal lobules, claustrum-superior temporal gyrus, and superior frontal gyrus-17 lentiform nucleus. Considering the previous findings on the functions of these regions 18 and the present results, it is suggested that the increase in FC may reflect brain processes 19 such as enhanced interoceptive awareness to one's own bodily state, a neuroplastic 20 change in visual processing circuits, and/or the maintenance of visual spatial memory.

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