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Experience influences how we perceive the world, how we interact with our environment, and how we develop. In fact, almost all animals can modify their behavior as a result of experience. Psychologists have long distinguished between different forms of learning and memory, and later determined that they are encoded in distinct brain areas. Neuroscientists dating back to Santiago Ramón y Cajal suggested that learning and memory might be encoded as changes in synaptic connections between neurons, but it wasn’t until the second half of the 20th century that experimental evidence corroborated this idea. Specific firing patterns of neurons during learning results in strengthening or weakening of synapses, and morphological modifications that can lead to long lasting changes in neural circuits. The molecular mechanisms that drive these changes are remarkably conserved across vertebrates. However, understanding how synaptic plasticity is integrated at a network level remains a big challenge in neuroscience. Relatively few studies have focused on how neural circuits encode changes in behavior in a natural context. In this dissertation I present two such examples using calcium imaging and optogenetic techniques in larval zebrafish. First, in collaboration with others, I studied neural activity that drives the onset of the very first behavior of the fish, tail coiling. We characterized the transition of spontaneous activity in the spinal cord from a sporadic, uncorrelated state, to a regular and synchronized state. We determined that this transition occurred through coalescence of local microcircuits, and that inhibiting the early sporadic activity impaired normal development of the central pattern generator network. Second, I studied how experience of prey affects hunting behavior and underlying neural activity. I developed a paradigm to assess the effect of prior hunting on prey capture behavior and showed that experienced fish initiate more captures than their naïve counterparts. I next established that experience does not affect the ability of the fish to see prey. Rather, experience increases the probability that activity in visual areas will evoke a capture initiation. This is accomplished by increasing the impact of information transfer from visual to motor areas, possibly due to increased activity in forebrain areas for experienced fish. |
