Pyramidal cell responses to temporally structured stimuli: Experiments and computer simulations

Oscillations in the field potential recorded from piriform cortex can be broadly categorized into slow and fast frequency ranges. The slow wave is correlated with respiration and sniffing. During respiration it is typically in the 1-4 Hz range but during sniffing it increases in frequency and is often referred to as the theta rhythm (4-12 Hz). The faster oscillations (30-50 Hz, also called gamma) appear in response to odor stimuli and are always modulated by the slower rhythm. Oscillations in the field potential are believed to reflect synchronized synaptic input to the dendrites of pyramidal neurons in the piriform cortex. In this thesis I use experimental and computer simulation techniques to study the consequences of pyramidal cell input meant to approximate the temporal characteristics of cortical oscillations.; Because the precise control of synaptic inputs is not possible in an experimental preparation, I constructed a realistic simulation of a layer II pyramidal cell from piriform cortex where such control would be possible. The model was able to match a wide range of physiological behavior including subthreshold oscillations and responses to multiple levels of current injection. Spatio-temporal patterns of synaptic input that have been suggested to underlie gamma oscillations in piriform cortex were then used as input to the simulation. Results suggested that neurons were not able to reset to baseline states within the duration of a single gamma oscillation.; To determine how well current injections with the temporal characteristics of cortical oscillations might be represented in the spike trains of pyramidal cells, I used a reconstruction algorithm to estimate the structure of the stimulus from spike train data and to quantify the amount of stimulus information contained in the spikes. I found that stimuli filtered at frequencies of 0-10 Hz and 4-12 Hz were much better represented in the pyramidal cell spike trains than 0-40 Hz stimuli designed to include the entire range of cortical oscillations. The effects of norepinephrine on spike coding were also studied. I found that while norepinephrine increased the amount of stimulus information in the spike train, a change in decoding strategy to extract stimulus information was not required.