The role of glomeruli in the neural representation of odors: results from optical recording studies.
CG Galizia, R Menzel
Inst. Biologie - Neurobiologie, Fachbereich BioChemPharm, Freie Universität Berlin, D-14195 Berlin, Germany
Abstract
Odors are received by olfactory receptors, which send their axons to the first sensory neuropils, the antennal lobes (in insects) or the olfactory bulb (in vertebrates). From here, processed olfactory information is relayed to higher order brain centres. A striking similarity of the olfactory systems across animal phyla is the presence of glomeruli in this first sensory neuropil. Various experiments have shown that odors elicit a mosaic of activated glomeruli, suggesting that odor quality is coded in an ‘across glomeruli’ activity code. In recent years, studies using optical recording techniques have greatly improved our understanding of the resulting 'across glomeruli pattern', making it possible to simultaneously measure responses in several, often identifiable, glomeruli. For the honeybee Apis mellifera, a functional atlas of odor representation is being created: in this atlas, the glomeruli being activated by different odorants are named. Still, several limitations remain to be solved. In this paper, we review what optical recording of odor-evoked glomerular activity patterns has revealed so far, and discuss the necessary next steps, with emphasis on the honeybee.