Representations of olfactory information and circuit organizations of the olfactory system in insect brains

Abstract

The insect olfactory system shares many features with the vertebrate system and has been studied as an excellent model for olfactory information processing. Olfactory receptors have been identified molecularly and functionally and olfactory glomeruli have been revealed as functional units of the first order olfactory center. These findings have led to the understanding of so called “labeled line” processing and “combinatorial coding” as basic functions for olfactory processing. Recently, progress in research using Drosophila melanogaster has revealed detailed functions and circuit organizations for olfactory processing, especially with the understanding of the circuit structure of higher brain centers, changing our view of the olfactory processing. Recent findings have revealed the complete circuits of sex pheromone processing, innate odor valence representation, labeled line processing for ecologically relevant odors, dopamine modulation at the mushroom body output compartments and the comprehensive identification of lateral horn neurons. Here we review pheromone and general odor processing from the antennal lobe through higher brain centers such as the mushroom body and lateral horn to the behavioral output, with special reference to recent progress on the research in moths and fruit flies.