Abstract
How do physico-chemical stimulus features, perception, and physiology relate? Given the multi-layered and parallel architecture of brains, the question specifically is where physiological activity patterns correspond to stimulus features and/or perception. Perceived distances between six odour pairs are defined behaviourally from four independent odour recognition tasks. We find that, in register with the physico-chemical distances of these odours, perceived distances for 3-octanol and n-amylacetate are consistently smallest in all four tasks, while the other five odour pairs are about equally distinct. Optical imaging in the antennal lobe, using a calcium sensor transgenically expressed in only first-order sensory or only second-order olfactory projection neurons, reveals that 3-octanol and n-amylacetate are distinctly represented in sensory neurons, but appear merged in projection neurons. These results may suggest that within-antennal lobe processing funnels sensory signals into behaviourally meaningful categories, in register with the physico-chemical relatedness of the odours.
Highlights
A flourishing period of research over the past three decades has led to a reasonably detailed picture of how different odours can cause different activity patterns along the olfactory pathway [reviewed in 1–5]
A behavioural handle on perceived difference Our approach was to ask whether flies perceive a test odour as the same or as different from a previously learned olfactory stimulus
The relationship between olfactory perception and physiology has been elegantly studied in the honeybee [22]: One out of 16
Summary
A flourishing period of research over the past three decades has led to a reasonably detailed picture of how different odours can cause different activity patterns along the olfactory pathway [reviewed in 1–5]. Odours are detected by sensory neurons housed within sensillae on the third antennal segment and the maxillary palps These sensory neurons project to the antennal lobes, the functional equivalent of the olfactory bulb in vertebrates. Each sensory neuron typically expresses one functional Or receptor gene, endowing different types of sensory neuron with partially overlapping ligand profiles [6,7]. Those sensory neurons expressing a common Or receptor gene converge onto one glomerulus within the antennal lobe [8,9] For different odours, this entails combinatorially different activity patterns of glomeruli [10,11,12]. We ask at which stage of this pathway neuronal activity patterns correspond to perception in the fly [for a pioneering study in the bee: 22]
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