Oswald, Anne-Marie Michelle2013-11-082013-11-0820052005Source: Dissertation Abstracts International, Volume: 66-12, Section: B, page: 6459.http://hdl.handle.net/10393/29244http://dx.doi.org/10.20381/ruor-19665Processing of sensory input requires information transfer between neurons primarily via action potentials. The interaction between synaptic input and the ionic mechanisms of action potential generation leads to stereotyped sequences of action potential events. It is hypothesized that these spike sequences code for the sensory inputs. Spike trains often consist of sequences of single action potentials and clusters of action potentials or bursts. Investigations in this thesis are directed toward identifying candidate coding mechanisms in the processing of electrosensory input by pyramidal cells of the electrosensory lateral line lobe (ELL). These studies employ electrophysiological techniques combined with computational analysis and neural modeling to study the responses of pyramidal cells to mimics of electrosensory stimuli and feedback from higher brain centers. The major findings of this thesis are that the timing of isolated action potentials is correlated with a broad range of frequencies present in electrosensory stimuli whereas burst timing is correlated mainly with low frequency stimulus content. The timing of both single action potentials and bursts is reproducible and occurs with low variability in response to repeated stimulus presentations. In addition, within burst events, the time intervals between consecutive action potentials are correlated with stimulus intensity. Thus, bursts can detect low frequency stimulus events as well as estimate their intensity. Finally, feedback input to ELL pyramidal cells from higher brain regions is highly plastic. A subset of these feedback fibers synapse on the region of pyramidal cell dendrites that are responsible for burst generation; thus feedback synaptic input might modulate burst responses and perhaps enhance the detection of low frequency stimuli. The main conclusions of this thesis are that isolated action potentials and spike bursts code for different stimulus frequencies and that the time between burst spikes codes for the intensity of stimulus events. In addition, I speculate that feedback can modify coding by regulating bursting.228 p.enBiology, Neuroscience.Thesis