Characterizing network properties of the whole-brain Drosophila connectome

Characterizing the network properties of animal brains may lead to a better understanding of computation and information flow in these complex organs. However, to date very few whole-brain neuron-level reconstructions have been completed across organisms. The collaborative Flywire project1-2 has completed the proofreading of a connectome for a Drosophila female brain which contains both complete hemispheres of the central brain and includes neurons that receive inputs in the optic lobes. Here, we dissect the network properties of the complete central brain of the fruit fly. We characterized the distributions of synaptic connection weights and network motifs in 75 anatomically defined brain regions, or neuropils, and found that different neuropils have different network statistics. We constructed a projectome describing how connected these neuropils are to each other, and identified the dominant neurotransmitters exchanged between each neuropil pair. To group neurons by connectivity rather than by anatomy, we employed spectral clustering to sort neurons into modules. We found that many of these modules correspond to neuron classes with known biological functions. Finally, we identified groups of neurons which project across the midline, a population which likely plays a critical role in sending signals from one hemisphere of the brain to the other. Together, these results highlight how the topology of the anatomical neuronal network may direct and constrain the flow of information across the brain of the fly.