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Optical imaging of neuronal population dynamics in the leech central nervous system


The focus of my dissertation centers on how networks of neurons interact to generate behaviors in the medicinal leech. I used voltage-sensitive dye imaging to simultaneously record from large populations of individual neurons to ask three related questions: (1) When and in what neurons is the decision made to either swim or crawl in response to a sensory stimulus? (2) Can single neurons influence the decision between swimming and crawling? (3) Do the swimming and crawling central pattern generators (CPGs) exist as distinct neuronal circuits, or do they share some of the same circuitry in a multifunctional manner? The first question was addressed by analyzing population recordings of the time between when a stimulus is delivered and when the choice between swimming and crawling is made. The result of the analysis highlighted populations of neurons that discriminated between the two behaviors earlier than any single neuron. The second question was addressed by attempting to manipulate candidate decision-making neurons in this population. We found a neuron, cell 208, which was sufficient to bias the choice between swimming and crawling with intracellular current injection. Thus, cell 208 participates in the decision-making process. The third question was motivated by the need to understand how the two CPGs are organized. By recording ongoing swimming and crawling in the same preparation, we discovered that twice as many cells in a ganglion oscillated with crawling compared to swimming. Of the cells that oscillated with swimming, a large percentage also oscillated with crawling. We characterized two previously unidentified interneurons, one that has a multifunctional role in both swimming and crawling and one that is dedicated to crawling

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