Behavioral/Systems/Cognitive Olfactory Information Processing in the Drosophila Antennal Lobe: Anything Goes?

When an animal smells an odor, olfactory sensory neurons generate an activity pattern across olfactory glomeruli of the first sensory neuropil, the insect antennal lobe or the vertebrate olfactory bulb. Here, several networks of local neurons interact with sensory neurons and with output neurons—insect projection neurons, or vertebrate mitral/tufted cells. The extent and form of information processing taking place in these local networks has been subject of controversy. To investigate the role of local neurons in odor information processingwehaveused the calciumsensorG-CaMP toperform in vivo recordingsof odor-evoked spatiotemporal activitypatterns in five genetically defined neuron populations of the antennal lobe ofDrosophilamelanogaster: three distinct populations of local neurons (two GABAergic and one cholinergic), as well as sensory neurons and projection neurons. Odor-specific and concentration dependent spatio-temporal response patterns varied among neuron populations. Activity transfer differed along the olfactory pathway for different glomerulus–odor combinations:we found cases of profile broadening andof linear and complex transfer.Moreover, thediscriminability between the odors also varied across neuron populations and wasmaximal in projection neurons. Discriminatory power increased with higherodor concentrationsover awidedynamic range, butdecreasedat thehighest concentration.These results show the complexity and diversity of odor information processing mechanisms across olfactory glomeruli in the fly antennal lobe. Key words: olfactory processing; odor concentration; antennal lobe network; local neurons; Drosophila melanogaster; calcium imagin