Network plasticity in the honey bee antennal lobe during odor presentation

Abstract

Odorant processing presents multiple parallels across animal species, and insects became relevant models for the study of olfactory coding because of the tractability of the underlying neural circuits. Within the insect brain, odorants are received by olfactory sensory neurons and processed by the antennal lobe network. Such a network comprises multiple nodes, named glomeruli, that receive sensory information and are interconnected by local interneurons participating in shaping the neural representation of an odorant. The study of functional connectivity between the nodes of a sensory network in vivo is a challenging task that requires simultaneous recording from multiple nodes at high temporal resolutions. Here, we used fast two-photon microscopy to follow the calcium dynamics of antennal lobe glomeruli and applied Granger causality analysis to assess the functional directed connectivity among network nodes during and after olfactory stimulation. Our findings show that there is a significant causal coupling between network nodes also in the absence of olfactory stimulation. However, connectivity patterns change upon odorant arrival, showing an increase in connection density and conveying odorant-specific information. Furthermore, we show that causal functional connectivity is unique in individual subjects, and cannot be detected upon artificial glomerular scrambling across individuals. This demonstrates that network states do not consist solely of correlations of mean glomerular responses, which are known to be conserved across bees.