Magnetic eye tracking in mice

Abstract

Eye movements provide insights about a wide range of brain functions, from sensorimotor integration to cognition; hence, the measurement of eye movements is an important tool in neuroscience research. We describe a method, based on magnetic sensing, for measuring eye movements in head-fixed and freely moving mice. A small magnet was surgically implanted on the eye, and changes in the magnet angle as the eye rotated were detected by a magnetic field sensor. Systematic testing demonstrated high resolution measurements of eye position of <0.1°. Magnetic eye tracking offers several advantages over the well-established eye coil and video-oculography methods. Most notably, it provides the first method for reliable, high-resolution measurement of eye movements in freely moving mice, revealing increased eye movements and altered binocular coordination compared to head-fixed mice. Overall, magnetic eye tracking provides a lightweight, inexpensive, easily implemented, and high-resolution method suitable for a wide range of applications.

Dynamics of gaze control during prey capture in freely moving mice

“…Figure 2C shows example traces of the horizontal position of the two eyes (top), along with running speed of the mouse (bottom). As described previously [5][6][7] and analyzed below ( Figure 3D), the eyes are generally stable when the mouse is not moving. In addition, the raw traces reveal a pattern of eye movement wherein rapid correlated movements of the two eyes are superimposed on slower anti-correlated movements.…”

“…Many studies have reported a limited range of infrequent eye movements in head restrained mice [6,25,28,29] , consistent with the idea that eye movements are generally driven by head movement.…”

“…It is unclear, however, how mice regulate their gaze to accomplish these goals. Previous studies in freely moving rodents (rats and mice) have shown that eye movements largely serve to compensate for head movements [5][6][7][8] , presumably driven by the vestibulo-ocular reflex (VOR) present in nearly all species [9] . While this can serve to stabilize the visual scene during movement, it is not clear how this stabilization is integrated with the potential need to shift the gaze for behavioral goals, particularly because mice lack a specialized central fovea in the retina, and also have laterally facing eyes resulting in a relatively limited binocular field (roughly 40° as opposed to 135° in humans [10] ).…”

“…While this can serve to stabilize the visual scene during movement, it is not clear how this stabilization is integrated with the potential need to shift the gaze for behavioral goals, particularly because mice lack a specialized central fovea in the retina, and also have laterally facing eyes resulting in a relatively limited binocular field (roughly 40° as opposed to 135° in humans [10] ). In addition, because eye movements are altered in head-fixed configurations due to the lack of head movement [6,8] , understanding the mechanisms of gaze control and active visual search benefits from studies in freely moving behaviors.…”

Real-time contextual feedback for closed-loop control of navigation

“…Although these systems are fast and reliable, their spatial resolution is heavily limited by the number of sensors deployed. Despite the availability of various other sensors, including microwave based motion detectors [29] , ultrasonic microphones [30,31] , radiofrequency detectors [32] , global positioning systems [33] , and heat (infrared) sensors [34] , majority of existing tracking systems rely on video cameras, as they provide detailed images of whole bodies [4,[35][36][37][38] , [39] , individual limbs [40][41][42] , face and whisker motion [43] , and eye movements [44,45] . A major drawback, however, is that behavioral classification requires several image processing steps to detect and identify the object of interest which takes several tens of milliseconds using the current state-of-art algorithms and standard computing infrastructure.…”