A primary function of the brain is its ability to associate stimuli encountered in the environment with outcomes associated with those stimuli. This process is critically involved in a number of behaviors critical for survival, such as finding food, mate selection, and recognizing predators. Although a large number of studies have been dedicated to searching for reward-related signals in the human brain, little attention is paid to the role of the sensory cue itself in establishing associational links between cues and rewards. Indeed, without maintaining stimulus specificity associated with the reward value, the contextual meaning of the reward value would quickly be lost. The research proposed here aims to examine the neural mechanisms by which olfactory information cues become causally associated with reward value in the human brain. With the first experiment (Aim1), we will use a combination of gas chromatography/mass spectrometry (GC/MS) equipment, functional magnetic resonance imaging (fMRI), and olfactory psychophysical measurements to examine whether any of the molecular components that make up a natural food odor mixture are particularly relevant for driving the satiety-related behavioral response associated with the food odor itself. This experiment would provide novel insights into the mechanisms by which behavior can be driven by specific features of a complex stimulus, even when those features are not consciously accessible. In a second experiment (Aim 2), we will implement an olfactory classical conditioning paradigm in which odors are paired with varying levels of reward. We will use this design to test for the brain areas involved in the emergence of reward-related information over the course of learning. For both experiments, we will test whether signals associated with reward value can predict alterations in odor-evoked representation in sensory regions such as piriform cortex (Aim 3). Given its unique anatomical organization and intimate affiliation with limbic emotional brain regions, the olfactory system presents an excellent model system for examining appetitive learning processes.
The neural mechanisms by which the brain computes the reward value of sensory stimuli are critically involved in a number of vital ecological behaviors, such as feeding, learning, and decision-making. Disruption in these processes is associated with obesity, addiction, and risky behavior. Findings from the research proposed here could provide key evidence into the way in which the brain computes reward value from olfactory stimuli.
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