What you are describing is exactly how long-term potentiation/LTP (or depression/LTD, for that matter) is measured electrophysiologically.
Here's an example from a 1988 review by Nicoll et al:
Nicoll, R. A., Kauer, J. A., & Malenka, R. C. (1988). The current excitement in long term potentiation. Neuron, 1(2), 97-103.
The x-axis is time in minutes, the ...