Side-specific olfactory conditioning leads to more specific odor representation between sides but not within sides in the honeybee antennal lobes

Honeybees can be trained to associate odorants to sucrose reward by conditioning the proboscis extension re- sponse. Using this paradigm, we have recently shown that bees can solve a side-specific task: they learn simulta- neously to discriminate a reinforced odor A from a non- reinforced odor B at one antenna (AB) and the reversed problem at the other antenna (AB). Side-specific (AB/ BA) conditioning is an interesting tool to measure neuro- physiological changes due to olfactory learning because the same odorant is excitatory (CS) on one brain side and inhibitory (CS) on the opposite side. In the bee brain, the antennal lobe (AL) is the first olfactory relay where the olfac- tory memory is established. Using calcium imaging, we com- pared odor-evoked activity in the functional units, the glo- meruli, of the two ALs, both in naive and conditioned individ- uals. Each odor evoked a different pattern of glomerular activity, which was symmetrical between sides and highly conserved among naive animals. In conditioned bees, re- sponse patterns were overall symmetrical but showed more active glomeruli and topical differences between sides. By representing odor vectors in a virtual olfactory space whose dimensions are the responses of 23 identified glomeruli, we found that distances between odor representations on each brain side were significantly higher in conditioned than in naive bees, but only for CS and CS. However, the distance between CS and CS representations was equal to that of naive individuals. Our work suggests that side-specific con- ditioning decorrelates odor representations between AL sides but not between CS and CS within one AL. © 2003 IBRO. Published by Elsevier Ltd. All rights reserved.