Abstract
In the interaural direction, translational linear acceleration is loaded during lateral translational movement and gravitational acceleration is loaded during lateral tilting movement. These two types of acceleration induce eye movements via two kinds of otolith-ocular reflexes to compensate for movement and maintain clear vision: horizontal eye movement during translational movement, and torsional eye movement (torsion) during tilting movement. Although the two types of acceleration cannot be discriminated, the two otolith-ocular reflexes can distinguish them effectively. In the current study, we tested whether lateral-eyed mice exhibit both of these otolith-ocular reflexes. In addition, we propose a new index for assessing the otolith-ocular reflex in mice. During lateral translational movement, mice did not show appropriate horizontal eye movement, but exhibited unnecessary vertical torsion-like eye movement that compensated for the angle between the body axis and gravito-inertial acceleration (GIA; i.e., the sum of gravity and inertial force due to movement) by interpreting GIA as gravity. Using the new index (amplitude of vertical component of eye movement)/(angle between body axis and GIA), the mouse otolith-ocular reflex can be assessed without determining whether the otolith-ocular reflex is induced during translational movement or during tilting movement.
Highlights
In the interaural direction, translational linear acceleration is loaded during lateral translational movement and gravitational acceleration is loaded during lateral tilting movement
The population-based outcomes indicated that the amplitude of the vertical component was proportional to the magnitude of maximum linear acceleration in the interaural direction. (F) gravito-inertial acceleration (GIA) tilt angle
These results indicate that eye movement was induced by linear acceleration in the interaural direction
Summary
Translational linear acceleration is loaded during lateral translational movement and gravitational acceleration is loaded during lateral tilting movement. Linear acceleration is loaded during lateral translational motion, and gravity acceleration is loaded during lateral tilting movement. One type of otolith-ocular reflex induces horizontal eye movement during lateral translational motion[1] and the other type induces torsional eye movement (hereinafter called “torsion”) during lateral tilting movement[2]. We sought to examine whether lateral-eyed mice possess both types of otolith-ocular reflexes exhibited by species with progressive frontalization of the eyes, including humans and monkeys. We recorded movement of both eyes of the mouse using high-speed cameras and analysed the recorded images using an offline computer image analysis system These data represent the three-dimensional movement of both eyes during the motion shown in (A). The three-dimensional coordinates of the eye were defined as follows: the
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