The saccadic repertoire of larval zebrafish reveals kinematically distinct saccades that are used in specific behavioural contexts.

Abstract

Saccades are rapid eye movements that are used by all species with good vision. They have been extensively studied, especially in vertebrates, and are understood to be controlled by a conserved brainstem circuit. However, despite the fact that saccades play important roles during diverse visually guided behaviours, little is known about whether their properties, including the manner in which they are coordinated with head/body movements, vary in the context of different visuomotor tasks. Here, we characterise the saccadic repertoire of larval zebrafish and identify five saccade types, defined by systematic differences in kinematics and binocular coordination. Each type was differentially expressed during visually guided behaviours. Conjugate saccades form a large group that are used in at least four contexts: Fast phases of the optokinetic nystagmus, visual scanning in stationary animals, and to shift or maintain gaze during locomotion. Convergent saccades play a specialised role during hunting and are coordinated with body movements to foveate prey. Furthermore, conjugate and convergent saccades follow distinct velocity main sequence relationships and show differences in the millisecond coordination of the eyes and body, pointing to differences in underlying neurophysiology. In summary, this study reveals unexpected diversity in horizontal saccades and predicts saccade type-specific neural activity patterns. HighlightsO_LIKinematic analysis of thousands of rapid eye movements reveals five saccade types. C_LIO_LIConjugate saccades have at least four identifiable visual functions. C_LIO_LIConvergent saccades are coordinated with body movements to foveate prey. C_LIO_LITiming, kinematics and main sequence relationships indicate saccade type-specific neural control. C_LI