Input-output transformation of odour representation in the mouse olfactory bulb via inhibitory network activity
Thu-P1-016
Presented by: Tobias Ackels
Convergence of olfactory sensory neurons (OSNs) onto discrete glomeruli generates a topographic map of olfactory receptor identity in the olfactory bulb (OB). Sensory input activates stereotypical glomerular patterns determined by the molecular receptive range of individual glomeruli. The combinatorial code of activated glomeruli holds information about the identity of an odour stimulus, before being processed by central circuits. Within a glomerulus information gets transferred to OB output neurons (mitral and tufted cells (MTCs)) which in turn form synaptic connections with inhibitory granule cells (GCs) via their lateral dendrites.
Here we monitored glomerular input and output signals in mice in response to a panel of 48 odours that cover a wide range of chemical space using in vivo 2-photon Ca2+ imaging. We employed triple-transgenic mouse lines that either express GCaMP6f under the OMP-promoter (input) or the Tbet-promoter (output), alongside a fluorescently tagged M72 or O174 glomerulus. The resulting response profiles revealed higher and more structured correlations of activity patterns for the input (n = 148 glomeruli, 5 mice) compared to the output (n = 185 glomeruli, 13 mice). A similar decorrelation, or whitening, of odour representations from input to output has previously been observed in the zebrafish OB (Friedrich and Laurent, 2001) and has been attested to be mediated by inhibitory interneurons (Wanner and Friedrich, 2020).
To investigate potential mechanisms underlying the whitening that we observed, we created an artificial neural network (ANN) that models the contribution of GCs to the output signal. Our results show that implementing the modelled inhibitory GC-MTC connection faithfully recapitulates the physiological responses observed in vivo both in terms of level and pattern of decorrelation.
Here we monitored glomerular input and output signals in mice in response to a panel of 48 odours that cover a wide range of chemical space using in vivo 2-photon Ca2+ imaging. We employed triple-transgenic mouse lines that either express GCaMP6f under the OMP-promoter (input) or the Tbet-promoter (output), alongside a fluorescently tagged M72 or O174 glomerulus. The resulting response profiles revealed higher and more structured correlations of activity patterns for the input (n = 148 glomeruli, 5 mice) compared to the output (n = 185 glomeruli, 13 mice). A similar decorrelation, or whitening, of odour representations from input to output has previously been observed in the zebrafish OB (Friedrich and Laurent, 2001) and has been attested to be mediated by inhibitory interneurons (Wanner and Friedrich, 2020).
To investigate potential mechanisms underlying the whitening that we observed, we created an artificial neural network (ANN) that models the contribution of GCs to the output signal. Our results show that implementing the modelled inhibitory GC-MTC connection faithfully recapitulates the physiological responses observed in vivo both in terms of level and pattern of decorrelation.