Abstract

We use the zebrafish optomotor response as a model for understanding the neural basis of visually guided behaviors. We have created a new behavioral assay to identify visual stimuli that specifically drive basic motor patterns in zebrafish. These stimuli evoked consistent patterns of neural activity in the neurons projecting to the spinal cord, which we could map throughout the entire population using in vivo two-photon calcium imaging. We found that stimuli that drive distinct behaviors activated distinct subsets of projection neurons, consisting, in some cases, of just a few cells. This stands in contrast to the distributed activation seen for more complex behaviors. Furthermore, targeted cell by cell ablations of the neurons associated with evoked turns abolished the corresponding behavioral response. For a more systematic characterization of responses throughout the zebrafish brain, we have made transgenic lines with pan-neuronal expression of genetically-encoded calcium indicators. Fish expressing the indicator GCaMP2 show responses with high signal to noise allowing stimulus tuning of neurons to be measured reliably, even with a single presentation. This opens up the possibility of functionally mapping a complete vertebrate brain with cellular precision and provides a framework for identifying the complete circuit underlying a vertebrate behaviur.