Human olfactory discrimination learning and generalization

Porter, Daria Boratyn

doi:https://doi.org/10.21985/n2-113g-q395

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Human olfactory discrimination learning and generalization

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Stimulus generalization is a critical mechanism for facilitating behavioral flexibility. Generalization allows the brain to reduce computational demands that would otherwise be necessary to create unique representations for each and every encounter while allowing the ability to deal with the complexity of real-world situations. Stimulus generalization is a fundamental cognitive mechanism that underlies adaptive behavior, as decisions and behaviors are typically guided by expectations based on previous experiences. Extensive research in the field suggests that generalization is prevalent across all species and sensory domains. Still, very little information is known about how the human olfactory system generalizes across olfactory stimuli and which brain networks support this process. This thesis investigates human olfactory discrimination learning and generalization. We develop a novel olfactory discrimination learning paradigm and employ it, first, in two groups with varying outcomes and, second, during fMRI scanning. In Experiment 1, we use our paradigm to train two groups of participants to associate an odor mixture with either an aversive outcome or a neutral outcome, and test generalization responses to a range of odor mixtures. We find better olfactory discrimination learning occurs when odors are paired with aversive outcomes. Additionally, we show that generalization is modulated by outcome valence, with aversive outcomes resulting in narrower generalization gradients. In Experiment 2 we characterize the brain regions involved using our fear generalization paradigm. We first replicate our behavioral findings. Next, we identify the orbitofrontal cortex, hippocampus, piriform cortex, amygdala, and insula as regions that support olfactory generalization. Further, we show that both stimulus and outcome representations are reactivated in the OFC when outcome predictions are made. Overall, these experiments establish that olfactory generalization may be the active inference of associations between a stimulus and an outcome. We identify potential behavioral and neural mechanisms by which the human olfactory system generalizes previously learned associations. Our findings may inform future clinical studies in patient populations in which this process is maladaptive.

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