Neurons aren't simple little machines, axons talk to each other.

He and his colleagues first discovered individual nerve cells can fire off signals even in the absence of electrical stimulations in the cell body or dendrites. It's not always stimulus in, immediate action potential out. (Action potentials are the fundamental electrical signaling elements used by neurons; they are very brief changes in the membrane voltage of the neuron.)

"This cellular memory is a novelty," Spruston said. "The neuron is responding to the history of what happened to it in the minute or so before." Spruston and Sheffield found that the cellular memory is stored in the axon and the action potential is generated farther down the axon than they would have expected. Instead of being near the cell body it occurs toward the end of the axon.

Their studies of individual neurons (from the hippocampus and neocortex of mice) led to experiments with multiple neurons, which resulted in perhaps the biggest surprise of all. The researchers found that one axon can talk to another. They stimulated one neuron, and detected the persistent firing in the other unstimulated neuron.

No dendrites or cell bodies were involved in this communication. "The axons are talking to each other, but it's a complete mystery as to how it works," Spruston said. "The next big question is: how widespread is this behavior? Is this an oddity or does in happen in lots of neurons? We don't think it's rare, so it's important for us to understand under what conditions it occurs and how this happens."

The original article (paywall).

Assuming this is all true, how does it affect the feasibility of uploading? Anyone want to bet on whether things are even more complicated than the current discoveries?

ETA: It seems unlikely to me that you have to simulate every atom to upload a person, and more unlikely that it's enough to view neurons as binary switches. Is there any good way to think about how much abstraction you can get away with in uploading?

Yes, I know it's a vague standard. I'm not sure how good an upload needs to be. How good would be good enough for you?