The olfactory system has been optimized over evolutionary time to perform an exquisite function: analyze odorant molecules by their molecular features, and synthesize holistic representations of them when presented in complex mixtures. It has been estimated that the olfactory system is able to detect approximately 10,000 odors (Axel 1995) over a large range of concentrations. However, unlike the sense of hearing or vision, this modality has been elusive to psychophysical analysis because no simple set of physical properties, such as light wavelengths for sight or sound frequency for hearing, has been found. Rather, olfaction appears to be intrinsically multidimensional. Along with the multidimensional nature of olfaction, the striking similarity of different olfactory systems across phyla (Hildebrand and Shepherd 1997) suggests that its architecture has been optimized to reflect basic properties of olfactory stimuli.
The objective of this study is to analyze how odor intensity and odor quality information is encoded on the first stages of the olfactory pathway: the olfactory epithelium and the olfactory glomerular layer. To study the olfactory epithelium, we built computational models of olfactory receptor neuron (ORN) populations based on their experimental statistical distributions. These models are based on the detailed characterization of the odor concentration response of ORN populations reported by Rospars et al. (2003). To study the glomerular layer, we modeled the ORN axon projections and lateral inhibitory interactions occurring at the olfactory glomeruli. The odor intensity and odor quality information conveyed by these two stages of the olfactory system is evaluated using the information theory. We consider the amount of information transmitted as a measure of the efficiency of the coding strategy followed at each stage.
In this chapter we first present an introduction that contains background regarding the early stages of the olfactory system, the ORN models used in this work, and a description of the information theoretic measure used: the mutual information. Then, we present the three studies performed in this work. In Section 2.2, we study the coding of odor intensity at the olfactory epithelium. In the next section (2.3), we perform the odor intensity study at the following anatomical stage: the glomerular layer. Finally, in Section 2.4 the study of odor intensity is extended to odor quality as well and applied at the olfactory epithelium.
© 2013 by Taylor & Francis Group, LLC.