ACHEMS 2019
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SPLTRAK Abstract Submission
Associative olfactory fear learning alters spatiotemporal coding of olfactory bulb output cells
Jordan M. Ross & Max L. Fletcher
University of Tennessee Health Science Center, Memphis, TN, United States

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 fear of these stimuli remains unclear. Using awake wide-field calcium imaging of excitatory post-synaptic olfactory bulb (OB) cells, we established that the glomerular representations of neutral odorants become more similar to the representation of the CS following fear learning, possibly providing an initial neural basis for fear generalization. Additionally, we identified two distinct circuits mediating odor-shock glomerular enhancements; one associative learning-independent but CS-specific, and another that requires associative learning and supports global enhancements. As our glomerular imaging encompassed responses from heterogenous cell types, we are now focused on investigating the learning-induced alterations of specific OB cell populations. Using a similar fear learning paradigm in combination with awake 2-photon imaging, we demonstrate that responses of mitral cells, superficial tufted cells, and juxtaglomerular cells are differentially modulated following fear learning, which may support the previously identified distinct mechanisms of glomerular enhancements. Many of the changes are temporally dynamic, even persisting after odor offset, which reflects rich sculpting of somatic responses. Furthermore, fear learning potentiates mitral cell responses of non-CS odors, regardless of peak timing or initial polarity. This acts to increase the correlation between CS and non-CS responses, especially throughout the duration of the odor presentation which may be relevant to the behavioral time scales of generalized freezing.