Abstract
Motor learning is essential to maintain accurate behavioral responses. We used a larval zebrafish model to study ocular motor learning behaviors. During a sustained period of optokinetic stimulation in 5-day-old wild-type zebrafish larvae the slow-phase eye velocity decreased over time. Then interestingly, a long-lasting and robust negative optokinetic afternystagmus (OKAN) was evoked upon light extinction. The slow-phase velocity, the quick-phase frequency, and the decay time constant of the negative OKAN were dependent on the stimulus duration and the adaptation to the preceding optokinetic stimulation. Based on these results, we propose a sensory adaptation process during continued optokinetic stimulation, which, when the stimulus is removed, leads to a negative OKAN as the result of a changed retinal slip velocity set point, and thus, a sensorimotor memory. The pronounced negative OKAN in larval zebrafish not only provides a practical solution to the hitherto unsolved problems of observing negative OKAN, but also, and most importantly, can be readily applied as a powerful model for studying sensorimotor learning and memory in vertebrates.
Highlights
Motor learning is essential to maintain accurate behavioral responses
optokinetic stimulatory phase (OKN) and the resulting optokinetic afternystagmus (OKAN) under different stimulus conditions, we recorded the eye movements of the larval zebrafish during 3 phases: First a 5 min base line period in the dark, followed by 20 min of unidirectional 10 deg/sec optokinetic stimulation and another 20 min of darkness
We observed that the OKN responses of zebrafish show velocity adaptation in response to sustained visual stimulation, which, following the offset of the visual stimulus, is manifested as negative OKAN with shifted null position
Summary
Motor learning is essential to maintain accurate behavioral responses. We used a larval zebrafish model to study ocular motor learning behaviors. The slow-phase velocity, the quick-phase frequency, and the decay time constant of the negative OKAN were dependent on the stimulus duration and the adaptation to the preceding optokinetic stimulation. The optokinetic system, which produces reflexive eye tracking movements in response to full-field motion of the visual surround, provides advantageous means to study sensorimotor learning. This system is highly conserved across vertebrate species, and its main function is to stabilize the visual image on the retina, thereby allowing high-resolution vision[7,8]. Following the offset of visual stimulation, subjects continue to generate persistent eye movements in the dark – termed optokinetic afternystagmus (OKAN) – which are attributed to the velocity storage mechanism[11]. OKAN20,26, and by smooth pursuit afternystagmus in foveated animals, in which the eyes continue moving in the same direction as the previous foveal tracking behavior[27,28,29]
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