Rat Olfactory Bulb Mitral Cells Receive Sparse Glomerular Inputs

Abstract

Center-surround receptive fields are a fundamental unit of brain organization. It has been proposed that olfactory bulb mitral cells exhibit this functional circuitry, with excitation from one glomerulus and inhibition from a broad field of glomeruli within reach of the lateral dendrites. We investigated this hypothesis using a combination of in vivo intrinsic imaging, single-unit recording, and a large panel of odors. Assuming a broad inhibitory field, a mitral cell would be influenced by >100 contiguous glomeruli and should respond to many odors. Instead, the observed response rate was an order of magnitude lower. A quantitative model indicates that mitral cell responses can be explained by just a handful of glomeruli. These glomeruli are spatially dispersed on the bulb and represent a broad range of odor sensitivities. We conclude that mitral cells do not have center-surround receptive fields. Instead, each mitral cell performs a specific computation combining a small and diverse set of glomerular inputs.

Timescale-dependent shaping of correlation by olfactory bulb lateral inhibition

“…Unlike purely center-surround lateral inhibitory circuits (such as the retina) (55), olfactory bulb lateral inhibition is less topographically confined (11,56,57) and mitral cells can laterally influence distant cells (37,(58)(59)(60). Further, the reciprocal nature of dendrodendritic synapses in the olfactory bulb may facilitate the generation and activation of shared inputs.…”

In vivo vomeronasal stimulation reveals sensory encoding of conspecific and allospecific cues by the mouse accessory olfactory bulb

“…Unlike mitral cells in the main olfactory bulb (MOB), in which responses are shaped by input from one or a few receptor cell classes (11,12), AOB output neurons receive convergent inputs from multiple glomeruli (13,14). This architecture could provide a platform for integrative information processing that significantly differs from that observed in the main olfactory system.…”

Is the Olfactory Bulb Computationally Similar to the Retina?

“…Fantana et al (2008) found a few glomeruli that were activated by Յ20 odors, whereas the most broadly tuned mitral cells they encountered responded to at most 10 odors. This is consistent with receptor neurons being FIG. 1.…”

“…Recently, Fantana et al (2008) directly addressed this fundamental question by combining functional imaging of the bulb to record olfactory inputs with extracellular recordings of the bulbar output neurons, while delivering 200 different olfactory stimuli to the nose of anesthetized rats. Their conclusions about olfactory bulb function are quite different from a previous widely accepted model, which proposed a computational role for the bulb quite similar to that of the retina, as subsequently described (Yokoi et al 1995).…”

“…The question remains: Do granule cells give rise to lateral inhibition in the bulb? Fantana et al (2008) set out to answer this question. To illustrate their line of reasoning, based on the predictions of the lateral inhibition model, consider the diagram shown in Fig.…”