Processing of Odor Mixtures in the Drosophila Antennal Lobe Reveals both Global Inhibition and Glomerulus-Specific Interactions

In an appetitive context, honeybees (Apis mellifera) learn to associate odors with a reward of sucrose solution. If an odor is presented immediately before the sucrose, an elemental association is formed that enables the odor to release the proboscis extension response (PER). Olfactory conditioning of PER was used to study whether, beyond elemental associations, honeybees are able to process configural associations. Bees were trained in a positive and anegative patterning discrimination problem. In the first problem, single odorants were nonreinforced whereas the compound was reinforced. In the second problem, single odorants were reinforced whereas the compound was nonreinforced. We studied whether bees can solve these problems and whether the ratio between the number of presentations of the reinforced stimuli and the number of presentations of the nonreinforced stimuli affects discrimination. Honeybees differentiated reinforced and nonreinforced stimuli in positive and negative patterning discriminations. They thus can process configural associations. The variation of the ratio of reinforced to nonreinforced stimuli modulated the amount of differentiation. The assignment of singular codes to complex odor blends could be implemented at the neural level: When bees are stimulated with odor mixtures, the activation patterns evoked at the primary olfactory neuropile, the antennal lobe, may be combinations of the single odorant responses that are not necessarily fully additive.

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Antennal Lobe of the Honeybee

Handbook of Brain Microcircuits ◽

10.1093/med/9780190636111.003.0028 ◽

2017 ◽

pp. 345-352

Author(s):

Jürgen Rybak ◽

Randolf Menzel

Keyword(s):

Olfactory Receptor ◽

Antennal Lobe ◽

Activity Patterns ◽

Odor Concentration ◽

Large Numbers ◽

Odor Mixtures ◽

Functional Analog ◽

Basic Functions ◽

Receptor Neurons ◽

Vast Range

The antennal lobe (AL) of an insect is the functional analog of the olfactory bulb in mammals. The first-level synaptic interaction of large numbers of multiple types of olfactory receptor neurons (OSNs) with AL interneurons serves the function of reliably coding a vast range of odorants and their mixtures and the separation between odor identity and odor concentration. Honeybees learn and discriminate among a seemingly unlimited number of odors (natural and artificial), categorize odor mixtures as unique stimuli, identify odors within 250 ms and odor sequences within 6 ms, and generalize odors according to the respective combinatorial glomerulus activity patterns in the AL. Therefore, the AL is the first-order neuropil serving basic functions of odor discrimination, categorization, generalization, and learning. This chapter first describes the internal organization of the AL, its inputs, and its outputs, and then analyzes the local circuit of a prototypical glomerulus.

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