Abstract
Odors are rarely composed of a single compound, but rather contain a large and complex variety of chemical components. Often, these mixtures are perceived as having unique qualities that can be quite different than the combination of their components. In many cases, a majority of the components of a mixture cannot be individually identified. This synthetic processing of odor information suggests that individual component representations of the mixture must interact somewhere along the olfactory pathway. The anatomical nature of sensory neuron input into segregated glomeruli with the bulb suggests that initial input of odor information into the bulb is analytic. However, a large network of interneurons within the olfactory bulb could allow for mixture interactions via mechanisms such as lateral inhibition. Currently in mammals, it is unclear if postsynaptic mitral/tufted cell glomerular mixture responses reflect the analytical mixture input, or provide the initial basis for synthetic processing with the olfactory system. To address this, olfactory bulb glomerular binary mixture representations were compared to representations of each component using transgenic mice expressing the calcium indicator G-CaMP2 in olfactory bulb mitral/tufted cells. Overall, dorsal surface mixture representations showed little mixture interaction and often appeared as a simple combination of the component representations. Based on this, it is concluded that dorsal surface glomerular mixture representations remain largely analytical with nearly all component information preserved.
Highlights
Olfaction is considered a synthetic sense, with odors being perceived as unique, individual perceptions
As the glomerular layer is the site of information transfer from receptor neuron to output neuron within the bulb, it provides an ideal place to investigate if the complex mixture interactions observed in mitral cells can arise from lateral processing in the early stages of the olfactory bulb (OB)
With the odorants and concentrations used here, postsynaptic mixture-evoked maps appeared to reflect a simple combination of the maps evoked by each individual component with very little mixture interaction observed
Summary
Olfaction is considered a synthetic sense, with odors being perceived as unique, individual perceptions. This is most apparent in the case of mixtures, where identification of individual components of a mixture is difficult, especially as the number of components is increased [1]. While naturally occurring odorants are often composed of hundreds of components, the quality of many of the individual components is often not perceived in the mixture, a phenomenon known as mixture interaction. While evidence exists for interactions at the receptor level [2,3,4,5,6,7] recent imaging experiments suggest that olfactory sensory neuron input patterns onto the olfactory bulb (OB) are largely analytical with little component interaction [8,9,10]. More frequent and complex interactions have been observed in deeper levels, especially in olfactory output neurons [10,11,12,13,14,15] and olfactory cortex [12,14,16]
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