Figure 8.
Computational modeling of eye movements. A, Schematic depicting video recordings of eye movements in semi-intact X. laevis tadpole preparations during horizontal sinusoidal head rotation. B, Averaged eye positions (green, Eyepos) and corresponding sinusoidal fits (blue, sine fit) over a single cycle of sinusoidal head rotation at three different frequencies (at ±30°/s peak velocity). C, Schematic view of the model used to evaluate whether observed motoneuronal spike patterns sufficiently explain eye movement behavior. Left, Spikes recorded from different motoneurons; black: original recordings; red: 180° shifted version to account for the innervation of the antagonistic muscle. Middle, Time courses of simulated muscle contractions derived from spike trains in the left column. Right, Weighted sum (positive weights, wi) of muscle contractions fitted to original VOR eye movement recordings (green trace) in response to head rotation (black dashed trace) and resultant simulations of eye movements (blue trace). D, Contributions of Group I (blue) and Group II (magenta) motor units to the simulation of actual eye movements (green, Eyepos) at 0.1, 0.5, and 1 Hz head rotation. E, Explained variances for eye movement simulations from all neurons (black) and contributions of Group I (blue), Group II (magenta), spontaneously active (sa, gray), or silent (s, gray) abducens motor units to overall explained variance. Gray sine waves and dashed black/green vertical lines in B indicate head motion stimulus position (Hpos) and phase relation of the responses, respectively.