Abstract
We investigate the interplay of odor identity and concentration coding in the antennal lobe (AL) of the honeybee Apis mellifera. In this primary olfactory center of the honeybee brain, odors are encoded by the spatio-temporal response patterns of olfactory glomeruli. With rising odor concentration, further glomerular responses are recruited into the patterns, which affects distances between the patterns. Based on calcium-imaging recordings, we found that such pattern broadening renders distances between glomerular response patterns closer to chemical distances between the corresponding odor molecules. Our results offer an explanation for the honeybee's improved odor discrimination performance at higher odor concentrations.
Highlights
The nature of olfactory systems seems to inevitably entangle odor identity and concentration
(2) Pattern development along the concentration range is smooth, i.e., different concentrations of the same odor can be connected by straight lines in almost all cases. (3) odor response patterns are roughly sorted by chemicalsimilarity of the odors, in particular carbon chain length
The evidence gathered in this work suggests that (1) odor discrimination is improved at higher odor concentrations, as response pattern distances are better estimates of chemical distances (Figure 6), and that (2) generalization over concentration levels of the same odor is possible to some extent due to pattern continuity and smooth transitions between patterns for concentration levels of the same odor (Figure 2)
Summary
The nature of olfactory systems seems to inevitably entangle odor identity and concentration. The response patterns of olfactory glomeruli encode odor identity (Malnic et al, 1999; Galizia and Menzel, 2000; Wang et al, 2003; Falasconi et al, 2012), and more glomeruli join the response patterns with increasing odor concentration (Malnic et al, 1999; Wachowiak et al, 2002; Sachse and Galizia, 2003; Wang et al, 2003), i.e., patterns, as well as distances between patterns change. Optical imaging with calcium-sensitive fluorescent dyes is an established technique (Galizia et al, 1999b; Sachse and Galizia, 2003) for recording responses of many olfactory glomeruli simultaneously, rendering the honeybee a suitable model organism
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