Preference-Independent Encoding of Visual Saliency Within but Not Cross Features in the Mouse Superior Colliculus

Detecting conspicuous stimuli in a visual scene is crucial for animal survival, yet it remains debated how the brain encodes visual saliency. Here we investigate how visual saliency is represented in the superficial superior colliculus (sSC) of awake mice using two-photon calcium imaging. We report on a preference-independent saliency map in the sSC. Specifically, salient stimuli evoke stronger responses in both excitatory and inhibitory neurons compared to uniform stimuli, with similar encoding patterns observed in both neuron types. The largest response occurs when a salient stimulus is positioned at the receptive field center, with contextual effects extending ∼40° away from the center. The response amplitude correlates well with the saliency strength of stimuli and is not influenced by the orientation or motion direction preferences of neurons. However, saliency encoding does depend on specific visual features. Furthermore, neurons involved in saliency encoding exhibit weak orientation or direction selectivity, suggesting a complementary relationship between the saliency map and the feature map.