The mammalian hippocampus has been compared to a Global Positioning System (GPS) that enables spatial navigation. This notion has been primarily drawn from studies conducted in nocturnal mammals, such as rats; that lack many adaptations to daylight vision compared to diurnal primates. Here we demonstrate that during foraging in a 3D maze, the common marmoset, a new world diurnal primate with foveal, stereo-color vision, predominantly uses rapid head-gaze shifts while stationary to visually explore their surroundings and then navigates towards goals minimizing head movements. On the other hand, rats, move their head at low velocities while locomoting to explore the environment using their whiskers. These differences in exploration-navigation strategies reflect the two species' sensory adaptations to their ecological niches. In the marmoset hippocampus CA3/CA1 regions putative pyramidal neurons show selectivity for 3D view, head direction, and less for place, but mainly for combinations of these variables. Inhibitory interneurons are tuned to 3D angular head velocity and translation speed, with most cells showing mixed selectivity for both variables. Marmosets lack the rhythmic theta oscillations of local field potentials seen during locomotion in rats. Instead, they show resetting of theta oscillations triggered by head-gaze shifts that co-occurred with the activation of interneurons, followed by various modulations in the activity of pyramidal cells. Our results show that the marmoset visual exploration/navigation strategies and the hippocampal specializations supporting them diverge from those observed in rats, reflecting the far-sensing capabilities of the marmoset adaptations to diurnal vision. Thus, the marmoset hippocampus may be considered a GPS, but G is for gaze.

No abstract