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Abstract
This dissertation investigates several factors that influence the olfactory system from both sensory and cognitive perspectives. I examine how rats smell and perform olfactory tasks on behavioral and neural levels using appetitive tasks and local field potentials (LFPs), respectively. Study 1 (chapters 3, 4 and 5) tests how cognitive demand such as task difficulty interacts with olfactory stimulus similarity to modulate olfactory system dynamics and behavior. Olfactory system neurophysiology is strongly modified by the context in which animals identify odors. Rats and mice rely on enhanced olfactory bulb (OB) gamma oscillation (65-110 Hz) power to effectively perform discrimination of similar odors. However, previous research has shown that the degree to which rats amplify gamma oscillations, a signature of neural firing precision, varies across studies which employ different tasks, training protocols, and response requirements. Particularly concerning gamma band LFP oscillations (65-110 Hz) in the OB, I hypothesize that cognitive demand significantly affects rats’ behavior and modulates OB gamma oscillations. I tested this hypothesis by designing a variant of the two-alternative choice (TAC) discrimination task in which rats learn to identify two very similar and two very different odors with or without a visual cue that limits the decision space on each trial. Rats with the informative cue use longer sampling times and show lower power gamma oscillations than rats with a non-informative cue. Several other behavioral and neural differences separate the two groups of rats, including patterns of connectivity among olfactory and hippocampal areas and beta oscillation (15-30 Hz) power. Study 2 (chapter 6) investigates the interactions between the trigeminal system and olfactory system. Given that most odors also activate the trigeminal system to varying degrees, we examine how trigeminal input modulates olfactory perception in binary mixture perception. I find that trigeminal odorants tend to be overshadowed by less or non-trigeminal components in binary mixtures. Overall, this work serves to unfold the complex story of olfactory processing by showing that the olfactory system dynamically adjusts its state and works closely with systems like the limbic and trigeminal systems differently under different contexts.