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Abstract:
Animals typically perceive natural odor cues in their olfactory environment as a complex mixture
of chemically diverse components. In insects, the initial representation of an odor mixture
occurs in the first olfactory center of the brain, the antennal lobe (AL). The contribution of
single neurons to the processing of complex mixtures in insects, and in particular moths, is still
largely unknown. Using a novel multicomponent stimulus system to equilibrate component and
mixture concentrations according to vapor pressure, we performed intracellular recordings of
projection and interneurons in an attempt to quantitatively characterize mixture representation and
integration properties of single AL neurons in the moth. We found that the fine spatiotemporal
representation of 2–7 component mixtures among single neurons in the AL revealed a highly
combinatorial, non-linear process for coding host mixtures presumably shaped by the AL network:
82% of mixture responding projection neurons and local interneurons showed non-linear spike
frequencies in response to a defined host odor mixture, exhibiting an array of interactions
including suppression, hypoadditivity, and synergism. Our results indicate that odor mixtures
are represented by each cell as a unique combinatorial representation, and there is no general
rule by which the network computes the mixture in comparison to single components. On
the single neuron level, we show that those differences manifest in a variety of parameters,
including the spatial location, frequency, latency, and temporal pattern of the response kinetics.