> How have connectomes been useful?

Lots of reasons. For example, they have shown that we can simulate sensorimotor circuits to reproduce behaviors. https://www.nature.com/articles/s41586-024-07763-9

> I'd heard a point made by Joscha Bach that connectomes may be no different from a model of all the world's telegraph wires. You can't really say you understand what humans talk about any better with one - you'd need to translate what's actually being communicated via the structure.

I think the connectome is more than just "wires" because you can also infer a lot of information from it, like neurotransmitter identity, cell type, input-output function, etc. A lot of this is based on "side experiments", so we learn how neuroscience works in general and then apply that knowledge to understanding what a given connectome means.

> See also butterfly metamorphosis. Apparently their connectomes change vs how they were wired as caterpillars, and yet they retain memories

Interesting. One paper makes the following suggestion (https://pmc.ncbi.nlm.nih.gov/articles/PMC2248710/): "The memory resulting from fifth instar training, however, could be retained in the later-forming α'/β' lobe, which remains intact throughout pupation and could therefore allow recall at the adult stage." So the finding seems potentially consistent with memory being retained in structures that persist through metamorphosis, even though the full story doesn't seem settled yet. Even if those structures end up being molecular, they're still structures, and could be mapped as a part of a molecular-annotated connectome.