神経科学：ショウジョウバエの脳の完全な地図

The first wiring diagram of the whole brain of a fruit fly, containing around 140,000 neurons and over 50 million connections, is presented in Nature this week. The map is part of a collection of papers from the FlyWire Consortium. The work offers opportunities to study how the brain functions in greater detail than previously possible and paves the way for mapping the brains of other species.

Brain functions, which underlie a range of sophisticated behaviours, are driven by the activity of neurons and the connections between these brain cells. Mapping out these connections can offer insight into how the brain works. The fruit fly, Drosophila melanogaster, is a commonly used model organism for biomedical science and is an ideal starting point for drawing up a complete wiring diagram of neural circuits. Their brains contain around a million times fewer neurons than human brains, but the fruit fly displays a range of complex behaviours, from flying and navigation to social interactions. While partial maps have previously been constructed for the fruit fly, a complete map for the whole brain has been lacking.

The first complete wiring map, or connectome, of the fruit fly brain is described by Sebastian Seung, Mala Murthy and colleagues. Previously, the largest fruit fly connectome was derived from a ‘hemibrain’, containing around 20,000 neurons connected by around 14 million synapses. The new map from the FlyWire Consortium contains around seven times more neurons (139,255) and nearly four times more synapses (54.5 million). To make sense of the connectome, Davi Bock, Gregory Jefferis and colleagues provide an annotation of the neuronal classes, cell types and functional groups in a second paper. They identify more than 8,400 cell types, of which 4,581 are new (mostly from brain regions outside the previously studied hemibrain). Other papers in the collection shed light on how connectivity between specific neurons drives behaviours such as communication between brain regions or movement.

Together, the work enables the study of how brain function is determined by the structure of brain circuits, providing a valuable resource for neuroscience research. Moreover, the approaches used to construct the wiring diagram of the fruit fly brain set the stage for future large-scale connectome projects in other species, the authors conclude.
 

1. Dorkenwald, S., Matsliah, A., Sterling, A.R. et al. Neuronal wiring diagram of an adult brain. Nature 634, 124–138 (2024). https://doi.org/10.1038/s41586-024-07558-y
2. Schlegel, P., Yin, Y., Bates, A.S. et al. Whole-brain annotation and multi-connectome cell typing of Drosophila. Nature 634, 139–152 (2024). https://doi.org/10.1038/s41586-024-07686-5
3. Shiu, P.K., Sterne, G.R., Spiller, N. et al. A Drosophila computational brain model reveals sensorimotor processing. Nature 634, 210–219 (2024). https://doi.org/10.1038/s41586-024-07763-9
4. Seung, H.S. Predicting visual function by interpreting a neuronal wiring diagram. Nature 634, 113–123 (2024). https://doi.org/10.1038/s41586-024-07953-5
5. Garner, D., Kind, E., Lai, J.Y.H. et al. Connectomic reconstruction predicts visual features used for navigation. Nature 634, 181–190 (2024). https://doi.org/10.1038/s41586-024-07967-z