Sparse incomplete representations: A novel role for olfactory granule cells

TL;DR

This paper presents a model explaining how olfactory granule cells contribute to the emergence of sparse odor representations in the olfactory bulb through self-organization and incomplete stimulus encoding.

Contribution

It introduces a novel role for granule cells in creating incomplete odor representations that lead to sparse mitral cell responses, highlighting a new functional perspective.

Findings

Granule cells build incomplete odor representations.

Sparse mitral cell responses emerge from excitation-inhibition balance.

Transient responses may be less sparse than steady-state responses.

Abstract

Mitral cells of the olfactory bulb form sparse representations of the odorants and transmit this information to the cortex. The olfactory code carried by the mitral cells is sparser than the inputs that they receive. In this study we analyze the mechanisms and functional significance of sparse olfactory codes. We consider a model of olfactory bulb containing populations of excitatory mitral and inhibitory granule cells. We argue that sparse codes may emerge as a result of self organization in the network leading to the precise balance between mitral cells' excitatory inputs and inhibition provided by the granule cells. We propose a novel role for the olfactory granule cells. We show that these cells can build representations of odorant stimuli that are not fully accurate. Due to the incompleteness in the granule cell representation, the exact excitation-inhibition balance is established only for some mitral cells leading to sparse responses of the mitral cell. Our model suggests a functional significance to the dendrodendritic synapses that mediate interactions between mitral and granule cells. The model accounts for the sparse olfactory code in the steady state and predicts that transient dynamics may be less sparse.