A noninvasive electromagnetic perturbation approach to probe extraocular proprioception

Abstract

Extraocular proprioception has been shown to participate in spatial perception and binocular alignment. Yet the physiological approaches used to study this sensory signal are limited because proprioceptive signaling takes place at the same time as visuomotor signaling. It is critical to dissociate this sensory signal from other visuomotor events that accompany eye movements. We present a novel noninvasive and quantifiable method for probing extraocular proprioception independent of other visuomotor processing by attaching a rare-earth magnet to a real-time model eye and placing an electromagnet <20mm from the eye. An electromagnet can increase or decrease angular displacements and velocities of the model eye. Electromagnetic activation rapidly affected (<2ms) the rotation kinematics of the eye, which were correlated linearly with both the current supply and the distance of the electromagnet relative to the eye. This method circumvented the constraints of conventional physiological manipulation of extraocular proprioception, such as manually or mechanically tugging on the eye ball. It can be applied to produce the discrepancy between the intended and the executed eye movements, so that proprioceptive reafference signals are dissociated from corollary motor discharges and other visuomotor events.