I know a number of people who have undergone it, and I have spoken with doctors who employ the therapy on their bipolar patients.
The way I understand it, those of us with bipolar disorder have differences in the way our brain chemistry works. The neurotransmitters show up out of phase, and as a result, we get depressed and suicidal, as well as all the manic symptoms like paranoia and hallucinations and whatnot.
In order to fix us, they need to get chemistry sequence back in proper order. They have a number of tools to do this with. There are a number of places in the process where they can intervene in order to reset the process.
Electroshock induces a kind of seizure, which is like stopping the mental/chemical process entirely, with the hope that when it restarts, it can restart the proper way. It’s similar to what they do to folks whose hearts are not beating properly. The shock stops the heart and then they hope it will start in the correct sequence.
Just as with hearts, brains also don’t always restart properly, so they have to try it again or give up on the therapy. But it does work on occasion. And when it works, it does a really good job.
The problem is that you never know who it will work on because all of us are different and they don’t know how to predict these things yet. We just don’t know enough about brains. So they have to try it and see.
Electroshock should do exactly the same thing to a regular brain as it does to a maladjusted brain. It’s stop it and we hope it’ll start up in the proper sequence again. It is the same if you stopped and started a normal heart. You’d hope it would start up properly.
But they might not start up properly. This is why doctors say, “first, do no harm.” You never treat someone who doesn’t need treating. Not if you’re an ethical practitioner.
There is no predicting how a “normal” brain would react to electroshock. It seems likely that there would be the memory effects that others have discussed. It is also possible the brain might get moved into improper functioning. They could end up with their brain chemistry out of phase.