The brain is remarkably plastic, and can compensate for all sorts of damage ... right up until the point that it can’t. This is a tautology, but the point is that there usually aren’t any symptoms until these are fairly far developed, which is a big contributor to the fairly terrible prognoses, and the fact that deterioration after the first noticeable symptom is rapid. The effect is magnified in the young and those otherwise in good health, as they have more effective reserve.
