Seminar Owen Randlett
PhD, Harvard University
Habituation is a simple form of learning and memory, where animals learn to reduce their responses to repeated but harmless stimuli. While habituation is simple in concept, its exact implementation in the vertebrate brain is not clear. It could occur via a single plasticity event at a singular site in the circuit. Alternatively, more complex strategies that combine multiple mechanisms at various processing stages and sites could occur. To determine the mechanisms leading to habituation, I use a simple visual assay in larval zebrafish. Zebrafish initially respond vigorously to whole-field reductions in illumination (dark flashes), initiating one or multiple large angle turns. This response habituates to repeated dark flashes, forming a memory that lasts for up to 24 hours. To study this process we use whole-brain functional imaging, targeted Ca2+ imaging, and high-throughput quantitative behavioural analyses. Through these experiments, we have found that habituation cannot be explained by a single plasticity event, but rather occurs via multiple mechanisms that combine to modulate specific aspects of behaviour. These mechanisms operate through different molecular pathways, and act at different sites in the circuit. This demonstrates that considerable mechanistic complexity remains to be explored in even this simple habituation memory.