The activities of pairs of mammalian motor neurons (MNs) receiving varying degrees of common excitatory synaptic input were simulated to study the relationship between nearly-coincident spiking and common excitatory drive. The somatic membrane potential of each MN was modeled using a single compartment model. Each MN was modeled toreceive synaptic contacts from hundreds of pre-synaptic fibers. The percentage of pre-synaptic fibers that diverged to supply both MNs of a pair with common synaptic input could be varied from 0 (no common inputs) to 100% (all common inputs). Spikes trains on separate re-synaptic fibers were independent of one another and were modeled as realizations of renewal processes with mean firing rates (10 - 50Hz) resembling that associated with supra-spinal input. Maximum synaptic conductances and time constants were varied across synapsesto match experimentally observed somatic EPSPs. The number of active pre-synaptic fibers to each MN was adjusted in order that the firingrates of MNs were between 8 and 15 Hz. For each common input condition, 100 s of concurrent spiking activity of the MNs was usedto construct cross-correlation histograms. The sizes of the central peaks in the histograms were quantified using both the k' (Ellaway and Murthy 1985) and CIS (Nordstrom et al. 1992) indices ofsynchrony. Monotonically increasing linear relationships between the proportion of common synaptic input and the magnitude of synchronywere observed for both indices. For example, the model predicted that 10% common input would yield a CIS value of 0.27 whereas 100% commoninput would yield a CIS value of 1.5. These values are within the range of values observed experimentally. These results, therefore,provide a means to translate measures of nearly-coincident spiking into plausible renditions of synaptic connectivity.

The forced Oscillation Technique (FOT) can be used to measure lung impedance continuously during breathing. However, spectral overlap between the breathing waveform and the applied flow oscillation can be problematic if the frequency content of spontaneous breathing is unknown. This problem motivated us to develop a modification to the FOT system called the Tracked Breathing Trainer. The modification uses biofeedback to constrain subjects to breathe at a single predetermined frequency. This thesis investigates the engineering and physiological aspects of the modification we made. We studied 8 adult non-asthmatic and 8 adult asthmatic subjects. Three 16 s perturbatory flow oscillation signals ranging from 1-40 Hz were used on the subjects. Each subject received three trials per perturbation for both spontaneous and tracked breathing. We then fitted a resistance-elastance-inertance model of the lung to each data set. For non-asthmatic subjects, the average resistance (R) and elastance (E) values for the first spontaneous breathing trial were 2.5±0.15 cmH2O.s.ml-1 and 18.1±3.55 cmH2O.ml-1, and for the third spontaneous breathing trial were 2.4±0.12 cmH2O.s.ml-1 and 21.8±4 cmH2O.ml-1. R and E for the first tracked breathing trial were 2.3±0.21 cmH2O.s.ml-1 and 33.6±7.4 cmH2O.ml-1, and for the third tracked breathing trial were 2.4±0.14 cmH2O.s.ml-1 and 25.75±4.3 cmH2O.ml-1, respectively. For asthmatic subjects, the average R and E values for the first spontaneous breathing trial were 3.32±0.68 cmH2O.s.ml-1 and 39.13±9.8 cmH2O.ml-1, and for the third spontaneous breathing trial were 3.12±0.15 cmH2O.s.ml-1 and 39.91±6.2 cmH2O.ml-1. R and E for the first tracked breathing trial were 2.86±0.15 cmH2O.s.ml-1 and 32.47±4.1 cmH2O.ml-1, and for the third tracked breathing trial were 2.86±0.21 cmH2O.s.ml-1 and 33.89±10 cmH2O.ml-1, respectively. These results show that R was consistently lower during tracked breathing than spontaneous breathing in both non-asthmatic and asthmatic subjects. However, an increase in E was observed during tracked breathing. We suspect this effect may have resulted from dynamic hyperinflation. These results also show that R and E are reproducible with both spontaneous and tracked breathing, and that R and E were not noticeably different between both breathing maneuvers. We conclude that using biofeedback to control the breathing pattern during application of the FOT in normal subjects does not significantly affect impedance measurements, and thus may be useful for avoiding spectral overlap between FOT perturbations and the breathing pattern.