The Olfactory Bulb Facilitates Use of Category Bounds for Classification of Odorants in Different Intensity Groups.

Justin Losacco,Diego Restrepo,Nicholas M George,Naoki Hiratani

doi:10.3389/fncel.2020.613635

Abstract

Signal processing of odor inputs to the olfactory bulb (OB) changes through top-down modulation whose shaping of neural rhythms in response to changes in stimulus intensity is not understood. Here we asked whether the representation of a high vs. low intensity odorant in the OB by oscillatory neural activity changed as the animal learned to discriminate odorant concentration ranges in a go-no go task. We trained mice to discriminate between high vs. low concentration odorants by learning to lick to the rewarded group (low or high). We recorded the local field potential (LFP) in the OB of these mice and calculated the theta-referenced beta or gamma oscillation power (theta phase-referenced power, or tPRP). We found that as the mouse learned to differentiate odorant concentrations, tPRP diverged between trials for the rewarded vs. the unrewarded concentration range. For the proficient animal, linear discriminant analysis was able to predict the rewarded odorant group and the performance of this classifier correlated with the percent correct behavior in the odor concentration discrimination task. Interestingly, the behavioral response and decoding accuracy were asymmetric as a function of concentration when the rewarded stimulus was shifted between the high and low odorant concentration ranges. A model for decision making motivated by the statistics of OB activity that uses a single threshold in a logarithmic concentration scale displays this asymmetry. Taken together with previous studies on the intensity criteria for decisions on odorant concentrations, our finding suggests that OB oscillatory events facilitate decision making to classify concentrations using a single intensity criterion.

Highlights

IntroductionAssociative learning and changes in attention modulate circuit activity in early sensory processing areas such as the olfactory bulb (OB) (Doucette et al, 2011; Gschwend et al, 2015; Chu et al, 2016; Losacco et al, 2020), the lateral geniculate nucleus (Ling et al, 2015) and the primary visual cortex (Pakan et al, 2018; Henschke et al, 2020)
Do oscillations in the olfactory bulb (OB) encode odorant concentration ranges and does the accuracy of encoding change as mice learn to discriminate in the go-no go task? We used tetrodes to record local field potential (LFP) oscillations in the OB of mice learning to associate a range of odorant concentrations with a water reward
We studied changes in odorant signal processing in the OB of awake behaving mice learning to discriminate low and high concentration odorants in a go-no go task

Summary

Introduction

Associative learning and changes in attention modulate circuit activity in early sensory processing areas such as the OB (Doucette et al, 2011; Gschwend et al, 2015; Chu et al, 2016; Losacco et al, 2020), the lateral geniculate nucleus (Ling et al, 2015) and the primary visual cortex (Pakan et al, 2018; Henschke et al, 2020). In the OB, mitral cells change firing frequency and synchrony as mice learn to distinguish a rewarded odor from an unrewarded one (Doucette et al, 2011; Gire et al, 2013; Gschwend et al, 2015). This process aids in signal processing and improves stimulus decoding from neural activity. Mice were presented with six logarithmically spaced odorant concentrations (Wojcik and Sirotin, 2014) and they were rewarded when they licked a spout for 2 s in the presence of either the three highest or three lowest odorant concentrations (the rewarded stimulus)

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Conclusion