| The ability of the rat to distinguish among diverse odors is crucial for a variety of reproductive, feeding, and other essential behaviors. The goals of this dissertation were to investigate how odorants are represented by spatial patterns of activity in the rat olfactory bulb, and to determine whether these activity patterns underlie the ability of rats to discriminate among different odorants.; Intrinsic signal imaging was used to measure odorant-evoked spatial activity patterns in the olfactory bulbs of anesthetized rats. This technique enabled the responses of large population of glomeruli on the dorsal surface of the olfactory bulb to be optically recorded. Different odorants, as well as different odorant concentrations, produced discriminable activity patterns. Increasing the concentration of an odorant resulted in a recruitment of an increasing number of active glomeruli. Odorants that varied in structure activated distinct but often overlapping sets of glomeruli, with the most structurally similar odorants producing the most similar activity patterns.; Next, imaging experiments were performed while the rats were exposed to pairs of enantiomers. The responses to these odorant pairs revealed that changes in odorant structure alone are sufficient to activate distinct spatial bulbar activity patterns. Rats were able to behaviorally discriminate between these odorant pairs, indicating that the spatial patterns of active glomeruli could underlie the ability of rats to discriminate between these odorants.; To causally link these activity patterns to performance of an odor-guided behavior, chronically implanted stimulating electrodes were used to perturb bulbar activity patterns while rats performed an odor discrimination task. Rats were able to discriminate electrical stimulation of the bulb from no stimulus, as well as electrical stimulation at two different bulb sites. In one case, electrical stimulation at a site activated by a rewarded odorant biased the rat to respond more frequently, but did not alter the rat's behavior when the odorant was no longer associated with a reward. These experiments demonstrate the feasibility of using microstimulation to link olfactory bulb activity and odor perception.; Overall, the results support the hypothesis that spatial activity patterns in the olfactory bulb mediate the ability of rats to discriminate between odorants. |
