Note: I'm not an electrical engineer, I'm a materials engineer. So maybe this question has an obvious answer, but I couldn't find one with a Google search. I also have no idea if I tagged this properly, sorry!
I was reading through this open access paper on evolvable circuit components and was pretty much following it, right up until the demonstration section at the end. In the caption to the following figure, the authors note:
Measuring the current at the terminal where VIn1 is applied, as shown in panel c, causes the current from both inputs to have the same sign.
Why should the ammeter have that effect when it's moved from the position in a to the position in c?
(I'm also a bit confused by the final graph in b; does the negative current reading here imply that current is flowing back from ground when V2 is applied after training?)