Olfactory fear conditioning non-specifically enhances glomerular odor responses and increases representational overlap of learned and neutral odors

Associative fear learning produces fear toward the conditioned stimulus (CS) and often generalization, the expansion of fear from the CS to similar, unlearned stimuli. However, how fear learning affects early sensory processing of learned and unlearned stimuli in relation to behavioral fear responses to these stimuli remains unclear. We subjected mice to a classical olfactory fear conditioning paradigm and used awake, in vivo calcium imaging to quantify learning-induced changes in glomerular odor responses, which constitutes the first site of olfactory processing in the brain. The results demonstrate that olfactory fear learning non-specifically enhances glomerular odor representations in a learning-dependent manner and increases representational similarity between the CS and non-conditioned odors. This mechanism may prime the system towards generalization of learned fear. Additionally, CS-specific enhancements remain even when associative learning is blocked; suggesting two separate mechanisms lead to enhanced glomerular responses following odor-shock pairings.