A High-speed Measurement System for Treadmill Spherical Motion in Virtual Reality for Mice and a Robust Rotation Axis Estimation Algorithm Based on Spherical Geometry

Abstract

A head-fixed rodent virtual reality (VR) system allows imaging of neuronal activity from the brain during behavioral tasks. To accurately measure the complex two-dimensional behavior of animals, it is necessary to detect the motion of the spherical treadmill of the VR system with multiple sensors. However, commercial VR systems for rodents are not widely used; they are expensive and the algorithms used to calculate the motion of the spherical treadmill from sensor signals are not publicly available. We developed a system to detect the motion of a spherical treadmill at high-speed using two optical mice. The system can be used on a general-purpose VR platform. A novel algorithm to robustly calculate the rotation axis of the spherical treadmill using spherical geometry was also devised. This system enables accurate reconstruction of complex two-dimensional behaviors of animals. The system is open source, which should encourage the use of VR-based approaches for imaging brain activity in rodents during behavioral tasks.