Is there doubt as to whether a neuron can be represented computationally?
1. You have to solve the interaction problem (how does the mind interact with the physical world?)
2. You need to explain why the world is not physically closed without blatantly violating physical theory / natural laws.
3. From the fact that the mind is nonphysical, it does not follow that computationalism is false. On the contrary, I'd say that computationalism is still the best explanation of how human thinking works even for a dualist. (All the alternatives are quite mystical, except maybe for hypercomputationalism.)