It's not clear whether a parameter in a neural network maps cleanly onto a synapse in a biological brain.

I think it's becoming pretty clear that they don't. First, scientists uncovered many additional ways neurons interact with one another[1]. Second, it seems that individual neurons do way more computing than in the simplistic ANN models [2].

[1]: https://en.wikipedia.org/wiki/Ephaptic_coupling

[2]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5740076/l

It’s very clear that they don’t.

I remember reading about fruit fly brains and how we're at a point where we can computationally simulate them now, but I'm not sure where that went.

Anyone know?

Take a look at http://fruitflybrain.org/