We know quite a lot. For example, we know that brains have various different nueromodulatory pathways. Take for example dopamine reward mechanism that is being talked about more openly these day. Dopamine is literally secreted by various different parts of the brain and affect different pathways.
I don't think it is anywhere feasible to emulate anything resembling this in a computational neural network with fixed input and output neurons.
Dopamine is not permanent, though. We're talking about long-term synaptic plasticity, not short-term neurotransmitter modulation.
Dopamine modulates long term potentiation and depression, in some complicated way.
Aren't we already emulating it? It's sort of a distributed and overlaid reward function, which we just undistributed