Yeah it's confusing to me too. Though I have heard that some mental symptoms do not necessarily mean it's from the brain itself, but can be caused by toxicity elsewhere, just as problems elsewhere can be created by brain mercury. E.g. hormonal problems and ongoing yeast can be indicative of brain mercury. Just as some mental symptoms maybe indicative of gut/liver toxicity.

My mental symptoms often got worse during detox. Each time you detox, you stir up the toxins and at the time you can feel like you're getting worse and it can make you feel like giving up. Either way, I felt bad anyway, so intensification of symptoms was often the sign that I was hitting the target, particularly when followed by some improvement, even if it was temporary, as more toxins would then rise to the surface and I'd feel bad again. But when you keep at it, those little patches of relief and improvement can start to increase further and last longer. It's just a case of persisting and not giving up.

Yeah, I too have heard that some cells are unable to regenerate. I'm not sure what to believe. But I think the body has amazing healing powers if it is given the chance and sources of toxicity are removed and existing toxicity is "detoxed" and reduced enough for health to start shining through again. One may never be 100%, but if you're used to being so chronically ill, then any improvement can feel dramatic!