title: Saccadic and Postsaccadic Disconjugacy in Zebrafish Larvae Suggests Independent Eye Movement Control.
abstract: Spontaneous eye movements of zebrafish larvae in the dark consist of centrifugal saccades that move the eyes from a central to an eccentric position and postsaccadic centripetal drifts. In a previous study, we showed that the fitted single-exponential time constants of the postsaccadic drifts are longer in the temporal-to-nasal (T->N) direction than in the nasal-to-temporal (N->T) direction. In the present study, we further report that saccadic peak velocities are higher and saccadic amplitudes are larger in the N->T direction than in the T->N direction. We investigated the underlying mechanism of this ocular disconjugacy in the dark with a top-down approach. A mathematic ocular motor model, including an eye plant, a set of burst neurons and a velocity-to-position neural integrator (VPNI), was built to simulate the typical larval eye movements in the dark. The modeling parameters, such as VPNI time constants, neural impulse signals generated by the burst neurons and time constants of the eye plant, were iteratively adjusted to fit the average saccadic eye movement. These simulations suggest that four pools of burst neurons and four pools of VPNIs are needed to explain the disconjugate eye movements in our results. A premotor mechanism controls the synchronous timing of binocular saccades, but the pools of burst and integrator neurons in zebrafish larvae seem to be different (and maybe separate) for both eyes and horizontal directions, which leads to the observed ocular disconjugacies during saccades and postsaccadic drifts in the dark.
authors.affiliation: Department of Neurology, University Hospital Zurich, University of ZurichZurich, Switzerland; PhD Program in Integrative Molecular Medicine, Life Science Graduate School, University of ZurichZurich, Switzerland.
authors.forename: Chien-Cheng
authors.initials: CC
authors.lastname: Chen
authors.affiliation: Department of Neurology, University Hospital Zurich, University of ZurichZurich, Switzerland; Department of Ophthalmology, University Hospital Zurich, University of ZurichZurich, Switzerland; Department of Otorhinolaryngology, University Hospital Zurich, University of ZurichZurich, Switzerland.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Bockisch
authors.affiliation: Department of Neurology, University Hospital Zurich, University of ZurichZurich, Switzerland; Zurich Center for Integrative Human Physiology (ZIHP), University of ZurichZurich, Switzerland; Neuroscience Center Zurich (ZNZ), University of Zurich and ETH ZurichZurich, Switzerland.
authors.forename: Dominik
authors.initials: D
authors.lastname: Straumann
authors.affiliation: Department of Neurology, University Hospital Zurich, University of ZurichZurich, Switzerland; Zurich Center for Integrative Human Physiology (ZIHP), University of ZurichZurich, Switzerland; Neuroscience Center Zurich (ZNZ), University of Zurich and ETH ZurichZurich, Switzerland.
authors.forename: Melody Ying-Yu
authors.initials: MY
authors.lastname: Huang
keywords: brainstem; gaze holding; larvae; ocular motor; saccades; zebrafish