Stimulus-driven rivalry among V1 neurons.

Binocular rivalry (BR) is a fascinating phenomenon that occurs when the two eyes are presented with dissimilar images, causing observers to perceive continuous alternations between the two images. During BR, cortical activation relies on both stimulus factors (e.g., incongruency), and top-down cognitive factors (e.g., attention). However, differentiating the influences of these factors has been proven challenging. Anesthetized animals provide a valuable model for studying pure stimulus-driven neural activity, free from high-level cognitive and behavioral influences. Using two-photon calcium imaging, we recorded neuronal responses to BR stimuli in V1 and V2 of anesthetized macaques. Under BR stimulation, V1 neurons exhibited continuous fluctuations in response, with varying fluctuation strengths that similar to their activity under stimulus alternation (SA) conditions. The main features of the fluctuations mirrored those observed in BR perception. The fluctuation strength of different neurons was associated with their ocular dominance and orientation selectivity. Similar observations in V2 suggest that such rivalry activity was successfully propagated along the visual pathway. These findings indicate that stimulus processing mechanisms in V1 are capable of generating rivalry-like alternations in the absence of consciousness.