Differential coding by two olfactory subsystems in the honeybee brain.

Sensory systems use parallel processing to extract and process different features of environmental stimuli. Parallel processing has been studied in the auditory, visual, and somatosensory systems, but equivalent research in the olfactory modality is scarce. The honeybee Apis mellifera is an interesting model for such research as its relatively simple brain contains a dual olfactory system, with a clear neural dichotomy from the periphery to higher-order centers, based on two main neuronal tracts [medial (m) and lateral (l) antenno-protocerebral tract (APT)]. The function of this dual system is as yet unknown, and attributes like odor quality and odor quantity might be separately encoded in these subsystems. We have thus studied olfactory coding at the input of both subsystems, using in vivo calcium imaging. As one of the subsystems (m-APT) has never been imaged before, a novel imaging preparation was developed to this end, and responses to a panel of aliphatic odorants at different concentrations were compared in both subsystems. Our data show a global redundancy of olfactory coding at the input of both subsystems but unravel some specificities for encoding chemical group and carbon chain length of odor molecules.