If you are weight lifting to muscle fatigue as in body building regimens, you may be causing too much muscle cell breakdown. You also may be just getting to much adrenaline flowing through your body which can over-stress your brain. Either one could cause the foggy feelings.

You will likely do better with lighter weights with more reps than heavier weights to fatigue.

Regarding neuroplasticity, I would like to see some research about where neuroplasticity abounds and where it is less likely. From what I have read, most neuroplasticity claims refer to a brains ability to develop skills later in life that would have more normally developed during youthful maturing.

There is a big difference between repairing damaged brain circuits and developing or strengthening under-developed brain skills. Most research appears to focus on the later concept of neuroplasticity.

To a person with PCS, there is a good value to neuroplasticity. Those under-developed brain circuits can be strengthened to help overcome the other weaknesses that resulted from the brain injury. A comparison would be, If you have injured and permanently lost function and strength in your right arm and hand, you can strengthen and improve function in your left arm and hand to compensate.