Vision to Action: Neural Circuits for Action Selection in Zebrafish


April 7, 2016 - 12:00pm
Northwest B103
About the Speaker
Herwig Baier (MPI Martinsried)

Visual images are transmitted to the brain via the axons of retinal ganglion cells (RGCs). These projections build representations of the identity and location of visual objects. We constructed a comprehensive map of the connectivity between RGCs and all retinorecipient areas in the midbrain and forebrain. By unbiased sparse genetic labeling and in vivo imaging, we identified >50 RGC types based on the combination of axonal targets and dendrite stratification patterns. This number far exceeds current estimates of RGC diversity derived from work in other vertebrates. We found that a dot moving horizontally across an LED screen evoked prey-capture maneuvers in immobilized fish larvae. This response is selectively tuned to size and speed of the stimulus. With two-photon GCaMP6 imaging, we identified a pretectal area that responded robustly to the optimal prey stimulus. Laser ablations showed that this area is necessary for prey-catching behavior. Interestingly, the RGCs projecting to this area fall into just two morphological classes. We similarly identified distinct pathways for the detection of looming visual stimuli and optic flow. Genetic labeling, optogenetic perturbations and imaging of downstream neurons are beginning to reveal the circuits underlying specific visuomotor transformations. Interestingly, decisions between approach and avoidance of a visual stimulus are influenced by hunger and stress. Behavioral changes are paralleled by changes in the processing of prey cues in the visual centers. Thus, the zebrafish system not only offers an entry point into the hardwired circuitry, but also into the neuromodulatory mechanisms that shape cognition, motivation and emotion in the vertebrate brain.