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Abstract

Rats are binocular animals and although their eyes are located laterally on the head they have a very large region of binocular overlap that extends from below their snouts to behind their head. How this enormous binocular field behaves as the animal navigates through an environment and what advantage this provides is completely unknown because to date there have been no recordings of the movements of both eyes in a freely moving rodent. Eye movements in head-restrained rats are conjugate similar to those of primates, but studies of the vestibular-ocular reflex in rats suggest that this only describes a fraction of their eye movements. Our lab studies how rodents use their vision to make decisions and the cortical circuits that are activated. Studying the cortex in the freely moving animal gives not only gives access to the suite of systems that allows the animal to make sense of the surrounding environment but it also enables the measurement of the behavioral strategies the animal uses when making decisions. In order to measure both activity from cortical populations and head and eye positions in the freely moving animal we further developed our miniature 2-photon microscope to include two lightweight cameras for ocular videography and a head tracking system. Using this approach we show that movements of the two eyes in freely moving rats differ fundamentally from the precisely controlled eye movements used by other mammals to maintain continuous ocular alignment.