Stimulus-driven rivalry among V1 neurons

Binocular rivalry (BR) is a fascinating phenomenon in which the presentation of two different images to each eye leads to alternating perceptual experiences. During BR, cortical activation is influenced by both stimulus-related factors (e.g., image incongruence) and top-down cognitive processes such as attention. Disentangling the contributions of these factors has remained a challenge. Anesthetized animal models offer a unique opportunity to isolate purely stimulus-driven neural activity, eliminating confounds from higher cognitive and behavioral processes. Using two-photon calcium imaging, we recorded neuronal responses to BR stimuli in areas V1 and V2 of anesthetized macaques. We found that under BR stimulation, V1 neurons exhibited ongoing response fluctuations whose magnitude varied across cells and closely resembled activity patterns during physical stimulus alternation (SA). Key characteristics of these fluctuations mirrored those typical of perceptual BR. The strength of fluctuation in individual neurons correlated with their ocular dominance and orientation selectivity. Similar patterns observed in V2 suggest that such rivalry-like activity propagates along the visual hierarchy. Together, these results demonstrate that early sensory mechanisms in V1 can generate BR-like alternations independently of conscious processing.