The problem isn't the number of neurons and their connections, but the complexity and diversity of them. There are hundreds of signalling molecules and recepto

The problem isn't the number of neurons and their connections, but the complexity and diversity of them. There are hundreds of signalling molecules and receptors that haven't been characterised. Some molecules diffuse over long distances, others are taken up and recycled depending on the local environment. Surrounding non-neuronal cells alter the ionic and metabolic states of networks, and can physically block (or sometimes actively transport) neurotransmitters. Each neuron type has its own response characteristics (activation function) that can completely change depending on the context. Even different locations on the same neuron have different receptors and transmitters, and can alternate between inhibitory or excitatory functions. To give an example of the difficulty, we've had a complete map of the neural connectivity of C. elegans for 30 years, which consists of only 302 neurons, and we still don't know how many of the cells and circuits function. I think the only solution will be high-throughput phenotyping. Test cell types and mutants under different circumstances until we have a deep-enough understand of these systems and their interactions to model them. It takes humans far too long to do experiments. We need more lab automation.