The Drosophila connectome is a complete list of the roughly 135,000 neurons in the brain of the fruit fly Drosophila melanogaster, along with all of the connections (synapses) between these neurons. As of 2013, the Drosophila connectome is a work in progress. Portions of two of the 76 compartments of the Drosophila brain have connectomes available, and others are subjects of ongoing study.
Connectome research (connectomics) has a number of competing objectives. On the one hand, investigators prefer an organism small enough that the connectome can be obtained in a reasonable amount of time. This argues for a small creature. On the other hand, one of the main uses of a connectome is to relate structure and behavior, so an animal with a large behavioral repertoire is desirable. It's also very helpful to use an animal with a large existing community of experimentalists, and many available genetic tools. Drosophila looks very good on these counts:
- The brain contains about 135,000 neurons, small enough to be reconstructed in the near future.
- The fruit fly exhibits many complex behaviors. Hundreds of different behaviors (feeding, grooming, flying, mating, learning, and so on) have been qualitatively and quantitatively studied over the years.
- The genetics of the fruit fly are well understood, and many (tens of thousands) of genetic variants are available.
- There are many electrophysiology, calcium imaging, and other studies ongoing with Drosophila.
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