Dense encoding of natural odorants by ensembles of sparsely activated neurons in the olfactory bulb.
Sensory information undergoes substantial transformation along sensory pathways, usually encompassing sparsening of activity. In the olfactory bulb, though natural odorants evoke dense glomerular input maps, mitral and tufted (M/T) cells tuning is considered to be sparse because of highly odor-specific firing rate change. However, experiments used to draw this conclusion were either based on recordings performed in anesthetized preparations or used monomolecular odorants presented at arbitrary concentrations. In this study, we evaluated the lifetime and population sparseness evoked by natural odorants by capturing spike temporal patterning of neuronal assemblies instead of individual M/T tonic activity. Using functional imaging and tetrode recordings in awake mice, we show that natural odorants at their native concentrations are encoded by broad assemblies of M/T cells. While reducing odorant concentrations, we observed a reduced number of activated glomeruli representations and consequently a narrowing of M/T tuning curves. We conclude that natural odorants at their native concentrations recruit M/T cells with phasic rather than tonic activity. When encoding odorants in assemblies, M/T cells carry information about a vast number of odorants (lifetime sparseness). In addition, each natural odorant activates a broad M/T cell assembly (population sparseness).
Department of Basic Neurosciences, Faculty of Medicine, University of Geneva, 1 rue Michel-Servet, 1211 Genève 4, Switzerland.|Geneva Neuroscience Center, University of Geneva, Switzerland.|Department of Genetics and Evolution, University of Geneva, 1211 Geneva, Switzerland.
Olivier
O
Gschwend
Department of Basic Neurosciences, Faculty of Medicine, University of Geneva, 1 rue Michel-Servet, 1211 Genève 4, Switzerland.|Geneva Neuroscience Center, University of Geneva, Switzerland.
Jonathan
J
Beroud
Department of Basic Neurosciences, Faculty of Medicine, University of Geneva, 1 rue Michel-Servet, 1211 Genève 4, Switzerland.|Geneva Neuroscience Center, University of Geneva, Switzerland.
Roberto
R
Vincis
Geneva Neuroscience Center, University of Geneva, Switzerland.|Department of Genetics and Evolution, University of Geneva, 1211 Geneva, Switzerland.
Ivan
I
Rodriguez
Department of Basic Neurosciences, Faculty of Medicine, University of Geneva, 1 rue Michel-Servet, 1211 Genève 4, Switzerland.|Geneva Neuroscience Center, University of Geneva, Switzerland.
Alan
A
Carleton
D000818:Animals; D005071:Evoked Potentials / Q000502:physiology*; D008297:Male; D051379:Mice; D009812:Odorants; D009830:Olfactory Bulb / Q000166:cytology / Q000502:physiology*; D055696:Olfactory Perception / Q000502:physiology*; D018035:Receptors, Odorant / Q000378:metabolism*; D011984:Sensory Receptor Cells / Q000166:cytology / Q000378:metabolism*
D018035:Receptors, Odorant