The Visual Umwelt of primates and Hippocampal Representations of Space.

Evolution sculpts the brain's sensory adaptations. Because these adaptations differ markedly across species, it is challenging for humans to fully comprehend how other animals perceive the world. For a nocturnal mouse, the subjective sensory world-its Umwelt-is dominated by odors, sounds, and textures, with visual input playing a secondary role. In contrast, the Umwelt of a diurnal primate is primarily visual, composed of colors, shapes, and hues, with less emphasis on olfaction, audition, or tactile cues. In mice and rats, hippocampal place cells are activated when the animal occupies specific locations in allocentric space. In contrast, studies in primates have identified hippocampal view cells, which respond when head-gaze is directed toward certain regions of visual space. The source of this divergence can be traced back to the evolution of mammalian species. Early mammals adapted to nocturnal environments to avoid predation by dinosaurs, becoming heavily dependent on olfaction, audition, touch, proprioception, and vestibular signals for perceiving changes in the environment, while regressing vision. However, one group of mammals started evolving stereoscopic foveal vision to capture insects and fruit in the arboreal environment. Following the mass extinction of dinosaurs, these primate ancestors transitioned to a diurnal niche, re-inventing color vision, which became their superpower. Stereo high-resolution color vision enabled primates to locate distant objects and landmarks efficiently, optimizing foraging while minimizing energy expenditure during navigation. The primate hippocampus then evolved to prioritize representations of visual scenes that support landmark-based navigation.