The relevance of linking neural activity patterns to perceptual tasks — a core objective of cognitive neuroscience — is highlighted by a new study in the honeybee Apis mellifera. Reporting in PloS Biology, Guerrieri, Schubert and colleagues show that odours that are encoded as physiologically similar are also perceived to be similar by bees.

To determine the perceptual similarity of odours, Guerrieri et al. adopted the olfactory conditioning of the proboscis extension response, a classical conditioning paradigm in which an olfactory stimulus (the conditioned stimulus, or CS) is paired with a sucrose feed until extension of the proboscis is evoked by the CS alone. They used 16 odours that varied in two chemical features: functional group and carbon-chain length. Each bee was conditioned to one of the odours and tested for generalization responses — in which different but similar stimuli are treated as equivalents — to four odours, one of which could be the trained odour.

The researchers found that all the odorants could be learned, and that generalization depended on functional group (for example, generalization was high from ketones to alcohols and aldehydes) and chain length (generalization was higher between long-chain than between short-chain odorants). They went on to build an olfactory perceptual space for the honeybee by principal components analysis (PCA), in which the relationships between odours were represented in a limited number of dimensions. The PCA showed a clear organization of odours depending on their chemical characteristics — functional group and chain length being 'inner dimensions' of the bees' olfactory space. Distances between odours in this perceptual space correlated with physiological distances — a measure of the similarity of odours based on neural activation patterns — obtained in optical imaging experiments of antennal lobe activity.

This study confirms that olfactory neural activity corresponds to olfactory perception, and shows how invertebrate models such as the honeybee can be used to answer fundamental questions about the neurobiology of perception. As this line of enquiry is pursued with more odours, comprising a range of molecular features, we will gain a more complete description of the honeybee's olfactory perceptual space, and a better understanding of how perceptual measures relate to patterns of neural activity.