GABAergic Fluctuations Predict Mixed Perception During Binocular Rivalry

Binocular rivalry occurs when two eyes compete for perceptual dominance, leading to alternating awareness of incompatible images over time. Previous studies have linked GABA+ concentrations in the visual cortex to rivalry dynamics and perceptual suppression, but it remains unclear whether perceptual changes are better explained by shifts in excitatory/inhibitory (E/I) balance or by neurochemical responses within specific pathways. Here, we use magnetic resonance spectroscopy to measure concentrations of Glx (glutamine + glutamate) and GABA+ in the visual cortex and a binocular rivalry paradigm to evaluate the effect of 60-min dark exposure on mixed perception and corresponding shifts in neurochemical concentrations in 14 normally sighted observers. Dark exposure increased the proportion of mixed perception and elevated Glx concentrations but did not produce significant changes in GABA+ concentrations or net E/I balance, as indexed by the Glx/GABA ratio. Dark exposure also did not significantly alter ocular dominance, phase durations, rivalry dynamics or perceptual alternation rates. Despite the absence of a group-level GABA+ effect, individual differences in mixed-perception changes were strongly associated with the magnitude of GABA+ fluctuations, whereas no comparable relationship was observed for Glx. These findings suggest that perceptual changes following dark exposure are more closely related to individual differences in GABA+ responses than to mean shifts in E/I balance. More broadly, the results suggest that binocular rivalry may be influenced by specific neurochemical responses that are not captured by directional measures of E/I balance alone, revealing a more nuanced relationship between neurochemistry and binocular perception.