Specifically an blockage type stroke. I get the blockage causes part of the brain tissue to die. As rehab happens and people get back some of their function, is that dead tissue regrowing again? Or is it just that other parts of the brain pick up the work of the dead tissue? Why some things come back and some never do?
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Hard to give a definitive answer on this one because there’s a lot of variety in how stroke patients recover and a lot of the underlying mechanisms are still unknown. There is a distinction in stroke care between “recovery” (when damaged neural circuits are replaced to innervate the affected tissue) and “compensation” (when the patient teaches themselves, consciously or not, to use different, unaffected muscle groups and their associated undamaged neural circuits for tasks that the damaged tissue used to handle). Occasionally people exhibit genuine recovery but it’s pretty rare. Generally time is a crucial factor – the longer neurons are deprived of oxygen, the less likely/able they are to recover, and starting physical therapy quicker is more likely to lead to recovery – but beyond that there is a lot of debate over what is the most effective course of treatment.
I used to work in a stroke lab (best job I ever had) and we got some good results suggesting that there was, at least in mice, what we called a “sensitive period.” We’d train them in a task they didn’t do natively but could learn (grasping food pellets with one paw), give them a small stroke in the part of the brain that controlled that paw which would destroy that ability, then see what we could do to help them relearn it. The mouse brain would respond to motor training within a day of the stroke with pretty decent recovery, but if you waited a week they’d never regain their ability. We also got an interesting result where if we injected them with a drug cocktail made of liquefied pig brain – a real shotgun approach, “who knows what signaling molecules might be helpful so let’s just use all of them!” – we could wait a week before training again and they’d relearn it about as well as those that got trained again immediately. But that was just in mice.
So, yeah, the best answer is pretty much “we don’t really know yet.” Sometimes people recover, usually they don’t, fast treatment helps but isn’t guaranteed. Part of the problem is that even with the vast amount of information we already have, medicine only has a pretty basic understanding of how the brain works. A guy named Emerson Pugh said something that I quote a lot – “If the brain were so simple that we could understand it, we would be so simple that we couldn’t.”
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