Something as simple as a prion can completely destroy it and then there's Phineas Gage, someone whom all neurobio students learn about on day one of their course. Neuroplasticity can be quite amazing.
I don't think it's exactly correct to say "a prion" can destroy it. One single prion I don't think would cause significant damage in most cases, if there could somehow be only a single one. The issue is that it's believed a prion will gradually cause nearby proteins to misfold and also become prions, and then it probably starts recurring exponentially like a pathogen infection, and your brain physically deteriorates and falls apart with no way to stop or reverse it. A very similar deterioration process appears to happen with other disorders like Alzheimer's and the form of dementia discussed in this article, though the root cause still isn't understood.
I don't have specific recommendations, but I think that the potential for recovery should be much higher than what people with neurodegenerative diseases suffer from, like what was described in this article.
There're a lot of risk and uncertainty trade-offs, and everyone reacts to things differently due to their genetics and what they're suffering from, but nootropic substances could potentially help here. They could possibly help as a short-term aid that improves memory and attention to detail while the nootropic is in effect, and some can actually potentially create long-term improvements.
They're very under-studied, and they definitely require a lot of careful research, gradual self-testing, and acceptance of some risk (some nootropics have almost no risk, and some have a moderate level), but it could be worth looking into.