Olfactory Information Processing in theDrosophilaAntennal Lobe: Anything Goes?

Abstract

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 processing we have used the calcium sensor G-CaMP to perform in vivo recordings of odor-evoked spatiotemporal activity patterns in five genetically defined neuron populations of the antennal lobe of Drosophila melanogaster: three distinct populations of local neurons (two GABAergic and one cholinergic), as well as sensory neurons and projection neurons. Odor-specific and concentration dependent spatiotemporal response patterns varied among neuron populations. Activity transfer differed along the olfactory pathway for different glomerulus-odor combinations: we found cases of profile broadening and of linear and complex transfer. Moreover, the discriminability between the odors also varied across neuron populations and was maximal in projection neurons. Discriminatory power increased with higher odor concentrations over a wide dynamic range, but decreased at the highest concentration. These results show the complexity and diversity of odor information processing mechanisms across olfactory glomeruli in the fly antennal lobe.

Olfactory Trace Conditioning inDrosophila

“…First, lateral movement was corrected by means of anatomical landmarks within and between measurements. Glomeruli were identified based on anatomical cues and on their response profiles (according to Silbering and Galizia, 2007;Silbering et al, 2008). The glomerular response patterns for 1-butanol and propionic acid corresponded well to the previously described response patterns (Silbering et al, 2008).…”

“…Glomeruli were identified based on anatomical cues and on their response profiles (according to Silbering and Galizia, 2007;Silbering et al, 2008). The glomerular response patterns for 1-butanol and propionic acid corresponded well to the previously described response patterns (Silbering et al, 2008). Glomerular responses were calculated by averaging the light intensity of 7 ϫ 7 pixels in the glomerulus center (corresponding to 6.3 ϫ 6.3 m).…”

“…3D). Post-odor ORN responses in Drosophila have been found previously (Hallem et al, 2004;Silbering and Galizia, 2007;Silbering et al, 2008), but their specificity and dynamics have not been studied in detail. Odors were presented using the same design as in the behavioral experiments, as 10-s-long pulses.…”

Data-driven honeybee antennal lobe model suggests how stimulus-onset asynchrony can aid odour segregation

“…We will here assume the same connectivity pattern for the bee. Within the AL, a network of intraand inter-glomerular inhibitory local neurons (LNs) and excitatory local neurons has been found to be involved in odour processing in the fly (Olsen et al, 2007;Shang et al, 2007;Silbering and Galizia, 2007;Silbering et al, 2008) and the bee (Sachse and Galizia, 2002). It is however currently unknown how the AL network contributes to odour segregation based on millisecond stimulus onset-asynchrony.…”

Learning pattern recognition and decision making in the insect brain

“…It is known that increasing odor concentrations recruit increasing numbers of glomeruli [86] and the activity of the projection neurons within the AL [87,88,89]. From the behavioral point of view, increasing the synapses of the local inhibitory neurons makes gases repulsive and to change the number of excitatory synapses makes odorants attractive [90].…”