Mechanisms of experience-dependent odor categorization in the olfactory cortex

Harvard Medical School, Boston MA

Investigators

Abstract

Project Summary / Abstract Olfaction is the dominant sense used by many animals to detect cues in the environment and generate appropriate responses, such as finding food and avoiding predators. To make sense of a complex, dynamic sensory environment, the brain uses of categorization, organizing related sensory representations into perceptual classes. In the case of olfaction, humans and other animals can group chemically distinct stimuli like lemon and lime into perceptual odor categories like citrus. It is unclear, however, how these categories are represented in the brain, or how they adapt with learning and experience. In the mammalian brain, relationships between odors are represented in the olfactory (piriform, PCx) cortex by correlated patterns of neural activity. The similarity of these cortical odor representations predicts odors’ perceptual similarity. Cortical relationships do not straightforwardly reflect chemical similarity, however. Rather, PCx re-organizes odor relationships relative to those in the sensory periphery and clusters representations of related odors. Odor responses in PCx have also been shown to be modulated by contextual factors like tasks and rewards, and preliminary work from the Datta lab suggests that PCx odor relationships may be modified by passive odor experience. Despite these insights, it is unclear how the structure of cortical odor space evolves over time with learning and experience. I hypothesize that relationships between odor representations in PCx are reorganized through experience to reflect associations between odors in the world and drive behaviorally relevant perceptual categorization. In Aim 1, I will explore how temporal odor associations influence neural and perceptual odor similarity. I will combine long-term electrophysiological recordings in PCx with behavioral assays of perception to examine whether odors which are repeatedly experienced together are represented more similarly in PCx and perceived more similarly. I will also utilize targeted genetic perturbations to examine the role of intracortical associative circuit plasticity in these changes. In Aim 2, I will investigate contextual odor associations to ask whether odors associated with the same context in an odor-visual virtual reality environment are represented and perceived more similarly. Together, these experiments will reveal how learning and experience shape odor representations in the mammalian olfactory cortex and provide broader insights the mechanisms of flexible sensory processing.