Stroke is a hellish cat gnawing its way through different disparate parts of the brain. Let's see how!!
The average stroke kills less than 3% of the total number of neurons in the brain. And that is way worse than it sounds. That small area of infarct insidiously exports itself to all reaches of the brain.
The first part of this process happens when the area surrounding the dead area (the penumbra) is "dragged into" the damaged part of the brain. And this surrounding area is not usually re-incorporated into the brains function. Through a process known as "learned nonuse," a healthcare system hell-bent (a lot of hell in this post sorry) – not on recovery – but rather on getting survivors to no longer be a burden on the healthcare system. And the word "burden" is euphemistic – it means cash.
Because the focus is on getting rid of the patient, and not recovery, the area surrounding the stroke is not used. And it is usually not used for the rest of the person's life. But the insidious nature is of stroke is not yet fully realized.
Many different areas of the brain outside of the dead zone, and the penumbra, are dragged into the mayhem. A process known as diaschisis takes over, and exports the damage to outpost throughout the brain. Why does this happen? Because the entire brain is interconnected, when one system goes down (The part of the brain killed by the stroke) and all the other areas connected to that dead zone also become either less functional or non-functional. Look at it this way: the classic neuroscience way of putting the way the brain operates is this: "neurons that fire together wired together." That means one part of the brain, if it communicates with a completely different part of the brain, we'll both benefit. If one of those area dies (as in stroke) the undamaged other area will also become less functional. But diaschisis is not the end of the story. The insidious nature the rambling and insidious nature of stroke marches on…
The next issue has to do with the strokes affect on the survivors life. After their stroke, survivors will typically become less socially engaged, less employable, less mobile, etc. The bad news is that the brain is designed to be socially engaged, engaged in productive activity, and to explore new things. The upshot of a less engaged brain is this: the entire brain goes through a literal "pruning". In fact, neuroscientists call this process a "pruning of the dendritic arbor." Throughout the brain neurons no longer use for the daily skills they once were, disengage from each other. In a sort of bad neuroplasticity, the brain becomes less capable. But, you guessed it, we're not done yet…
The final, and one of the worst and most insidious effects of the stroke is this: through a series of direct communication and chemical reactions, the "reptilian brain" is dragged into the evil march of stroke. Areas like the hippocampus and limbic system – areas that are responsible for emotions, and mood regulation, are also wracked by the stroke.
It is heartening, and it certainly is a point of view that I have promoted over the years, that the average stroke is really small. And the stroke sits in a highly redundant, and highly changeable (plastic) environment. All of that seems like good news. You have a small area of death, surrounded by a large family of neurons willing to take over for those that are killed by the stroke.
But the more I learn about stroke the more I understand that the stroke is not just the stroke. Echos of that small area reverberate. The ripple effect of that small area wraps its tentacles around-- and through-- the entire brain.