There's also the possibility that the abnormality isn't on the scale of a wire carrying high current vs no current; it could be a fairly subtle set of changes, with a high level of background signals. Furthermore, it's unlikely to be the exact same wiring pattern in the exact same place in all people.
I'm thinking of the pre-digital telephone system, where the cables consisted of a large number of individual wires woven together, connected in pairs through various switches for a given connection. I think you could get crosstalk between two conversations if the connections were in just the right--extremely unlikey but still possible--pattern. There would be no abnormality in the individual wires; it's the pattern as a whole responsible. Identifying the brain pattern responsible for ME's fatigue-like symptom might be impractical even after another hundred years of tech development. A huge hurricane might be caused by a specific butterly flap, but identifying which flap is not practical.
