Differentially Modifies Stimulus Encoding in Primary Sensory

22 Experience shapes both central olfactory system function and odor 23 perception. In piriform cortex, odor experience appears critical for 24 synthetic processing of odor mixtures which contributes to perceptual 25 learning and perceptual acuity, as well as contributing to memory for 26 events and/or rewards associated with odors. Here, we examined the effect 27 of odor fear conditioning on piriform cortical single-unit responses to the 28 learned aversive odor, as well as its effects on similar (overlapping mixtures) 29 in freely moving rats. We found that odor-evoked fear responses were 30 training paradigm-dependent. Simple association of a CS+ odor with foot-31 shock (US) led to generalized fear (cue-evoked freezing) to similar odors. 32 However, after differential conditioning, which included trials where a CS-33 odor (a mixture overlapping with the CS+) was not paired with shock, 34 freezing responses were CS+ odor-specific and less generalized. Pseudo-35 conditioning led to no odor-evoked freezing. These differential levels of 36 stimulus control over freezing were associated with different training-37 induced changes in single-unit odor responses in anterior piriform cortex 38 (aPCX). Both simple and differential conditioning induced a significant 39 decrease in aPCX single-unit spontaneous activity compared to pre-training 40 levels while pseudo-conditioning did not. Simple conditioning enhanced 41 mean receptive field size (breadth of tuning) of the aPCX units, while 42 differential conditioning reduced mean receptive field size. These results 43 suggest that generalized fear is associated with an impairment of olfactory 44 cortical discrimination. Furthermore, changes in sensory processing are 45 dependent on the nature of training, and can predict the stimulus 46 controlled behavioral outcome of the training.