Neural representation of 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 shown high color-discrimination accuracy in birds, it remains unclear whether higher-order visual areas organize color information in a structured manner. 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. Many entopallium sites exhibited robust hue selectivity that remained stable across luminance and saturation changes, and population responses were shaped mainly by gain modulation. These sites also showed 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 stronger than category-related correlations. These results suggest that the pigeon entopallium exhibits population-level color coding and produces a hue-related representational geometry that is broadly consistent with reports from primate V4 under comparable stimulus manipulations.