Animals actively interact with their environment to gather sensory information. There is conflicting evidence about how mice use vision to sample their environment. During head restraint, mice make rapid eye movements strongly coupled between the eyes, similar to conjugate saccadic eye movements in humans. However, when mice are free to move their heads, eye movement patterns are more complex and often non-conjugate, with the eyes moving in opposite directions. Here, we combined eye tracking with head motion measurements in freely moving mice and found that both observations can be explained by the existence of two distinct types of coupling between eye and head movements. The first type comprised non-conjugate eye movements which systematically compensated for changes in head tilt to maintain approximately the same visual field relative to the horizontal ground plane. The second type of eye movements were conjugate and coupled to head yaw rotation to produce a "saccade and fixate" gaze pattern. During head initiated saccades, the eyes moved together in the same direction as the head, but during subsequent fixation moved in the opposite direction to the head to compensate for head rotation. This "saccade and fixate" pattern is similar to that seen in humans who use eye movements (with or without head movement) to rapidly shift gaze but in mice relies on combined eye and head movements. Indeed, the two types of eye movements very rarely occurred in the absence of head movements. Even in head-restrained mice, eye movements were invariably associated with attempted head motion. Both types of eye-head coupling were seen in freely moving mice during social interactions and a visually-guided object tracking task. Our results reveal that mice use a combination of head and eye movements to sample their environment and highlight the similarities and differences between eye movements in mice and humans.

Two distinct types of eye-head coupling in freely moving mice