Neural Representation for Color-selective Populations in the Pigeon Entopallium

Understanding how birds encode object color is fundamental to elucidating the neural mechanisms of color vision. Although behavioral studies have demonstrated high color discrimination accuracy in birds, it remains unclear whether higher-order visual areas structurally encode color information. Here, we performed multi-site multi-unit activity recordings from the pigeon entopallium while presenting multi-category images that systematically varied in hue, luminance, and saturation. Numerous entopallium sites exhibited robust hue selectivity that remained stable across luminance and saturation changes, with population responses primarily gain modulation. Simultaneously, these sites demonstrated category-invariant color selectivity within the tested object set. Population-level analyses revealed a distinct and structured representational geometry that corresponded closely to perceptual color axes, with color-related correlations markedly stronger than category-related correlations. These results are consistent with the possibility that the pigeon entopallium contributes to population-level color coding, and that its hue-related population organization shares certain computational features with coding principles described in primate area V4.