Abstract
Humans and other animals can recognize an odorant as the same over a range of odorant concentrations. It remains unclear whether the olfactory bulb, the brain structure that mediates the first stage of olfactory information processing, participates in generating this perceptual concentration invariance. Olfactory bulb glomeruli are regions of neuropil that contain input and output processes: olfactory receptor neuron nerve terminals (input) and mitral/tufted cell apical dendrites (output). Differences between the input and output of a brain region define the function(s) carried out by that region. Here we compare the activity signals from the input and output across a range of odorant concentrations. The output maps maintain a relatively stable representation of odor identity over the tested concentration range, even though the input maps and signals change markedly. These results provide direct evidence that the mammalian olfactory bulb likely participates in generating the perception of concentration invariance of odor quality.
Highlights
The glomerular maps of the input to the olfactory bulb are a confound of odorant identity and odorant concentration[4, 5, 7,8,9], a result we have confirmed (Fig. 2, Supplementary Figs 2–4)
Our results show that odorant identity is more likely determined by the glomerular output of the olfactory bulb (Fig. 5)
The olfactory bulb in large part removes the qualitative effect of odorant concentration so that the output maps mainly represent odorant identity, the population average activity signal of the mitral and tufted cells connected to a glomerulus still encodes intensity differences
Summary
We carried out the input measurements in transgenic mice that express GCaMP6f in the olfactory receptor cell input (OMP-GCaMP6f) (Fig. 4a; Supplementary Fig. 1a–c; 11 hemi-bulbs in 7 preparations). In this comparison where the same sensor was used, both the input and output activity patterns, map correlations, and signal amplitudes as a function of concentration were similar to the results presented in Fig. 3 where different sensors were used but the comparison was made in individual mice.
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