The Investigation In Modulation Of Operant Learning By Visual Properties Of Conditioned Stimuli In Larval Zebrafish

How does the brain perform the learning behavior and form memory is a long-lasting fundamental question in neuroscience.Researchers have established many behavioral paradigms of learning behaviors,such as classical learning—a form of learning that links a neutral stimuli with a reward or punishment and operant learning-a form of learning that links the animals’ behavior with the consequences.However,the learning paradigms are mostly for mouse and other mammals.Recent years,the larval zebrafish has emerged as a promising vertebrate model organism to study neural mechanisms underlying learning and memory due to its small brain and rich behavioral repertoire.In addition,researchers have developed genetic tools,such as GAL4/UAS system in zebrafish.Genetic and optic manipulations are accessible in most cases.Here,we report on a high-throughput operant conditioning system for zebrafish larvae,which can simultaneously train twelve fish to associate a visual conditioned pattern with electroshocks in an automated workflow.We find that the learning responses can be enhanced by the visual contrast,not the spatial features of the conditioned patterns,highlighted by fish’s presence in the CS zone and the turning events that fish performed.By further characterizing the learning curves with the positional index,we demonstrate that the percentage of learners increase as the conditioned pattern becomes darker.Also,we quantified the memory extinction in our operant learning task and found that lower visual contrast between the conditioned pattern and the background elicits more fish with memory extinction,highlighted by the memory length.Moreover,little difference in operant learning responses was found between AB wild-type fish and elavl3:H2B-GCaMP6f transgenic fish.Finally,we conceive a future direction that combines imaging in freely swimming zebrafish with the behavioral paradigm to monitor the underlying neural activity.Ultimately,we want to understand the neural mechanisms of this learning process at the whole-brain circuit level.