Central processing of olfaction.

Studies on the properties of olfactory receptors and of the olfactory glomeruli indicate that there is spatial segregation of response to particular characteristics of odorant molecules at the input level of the olfactory bulb. Existing anatomical information and studies of synaptic mechanisms in the olfactory bulb suggest that the bulb circuitry might act as a contrast detection mechanism analyzing a spatially organized input. Recent electrophysiological studies have supported this idea. Extracellular recordings have shown that the similarity between responses of cell pairs to the same stimulus odor depend upon the distance between those cells. Intracellular recordings from mitral and tufted cells have shown spatially organized excitatory and inhibitory responses to localized electrical stimulation of the input layer of the bulb. Some of the major interneurons of the olfactory bulb have also been identified during odor and localized electrical stimulation. These recordings are also consistent with a spatially based organization.