A comparison of video and magnetic search coil recordings of mouse eye movements

Interest in connecting molecular biology and behavior is motivating research into the eye movements of mice. Unfortunately, recording eye movements in this diminutive animal is technically difficult. We present the first method for obtaining calibrated video oculography, and contrast the results with simultaneously obtained scleral search coil recordings in C57BL/6 pigmented mice. We determined the distance of the pupil from the center of corneal curvature, based upon relative motions of the pupil and corneal reflections during camera movements, and used the distance to convert subsequent video measurements of pupil motion to eye rotation. We recorded responses during sinusoidal rotation (0.1-1.6 Hz) in the light, by video prior to search coil implantation, and by video and search coil simultaneously following implantation. Pre-implantation, video-derived gains ranged from 0.86+/-0.03 (mean+/-SD) at 0.1 Hz to 0.95+/-0.03 at 0.8 Hz. Phase progressed monotonically from -3.1+/-2. 6 degrees (eye leads head) at 0.1 Hz to +5.9+/-1.1 degrees at 1.6 Hz. Coil implantation reduced the range of video-derived gains to 0. 64-0.79. This reduction reflects disruption of normal behavior by the coil. Coil data confirmed the video results. Video and search coil techniques each have advantages. Specific precautions are required when designing and interpreting experiments using the coil technique.