Honey bee antennal lobe calcium imaging

Odour processing exhibits multiple parallels between vertebrate and
invertebrate olfactory systems. Insects, in particular, have emerged as
relevant models for olfactory studies because of the tractability of their
olfactory circuits. Here, we used fast calcium imaging to track the
activity of projection neurons in the honey bee antennal lobe (AL) during
olfactory stimulation at high temporal resolution. We observed a
heterogeneity of response profiles and an abundance of inhibitory
activities, resulting in various response latencies and stimulus-specific
post-odour neural signatures. Recorded calcium signals were fed to a
mushroom body (MB) model constructed implementing the fundamental features
of connectivity between olfactory projection neurons, Kenyon cells (KC),
and MB output neurons (MBON). The model accounts for the increase of
odorant discrimination in the MB compared to the AL and reveals the
recruitment of two distinct KC populations that represent odorants and
their aftersmell as two separate but temporally coherent neural objects.
Finally, we showed that the learning-induced modulation of KC-to-MBON
synapses can explain both the variations in associative learning scores
across different conditioning protocols used in bees and the bees'
response latency. Thus, it provides a simple explanation of how the time
contingency between the stimulus and the reward can be encoded without the
need for time tracking. This study broadens our understanding of olfactory
coding and learning in honey bees. It demonstrates that a model based on
simple MB connectivity rules and fed with real physiological data can
explain fundamental aspects of odour processing and associative learning.