Increased blood flow to the brain after a microscopic stroke doesn't mean that part of the brain has recovered. At least not yet.
A study in Science Advances used advanced neural monitoring technology to discover a significant disconnect between how long it takes blood flow and brain function to recover in the region of a microinfarct, a tiny stroke in tissue less than 1 millimeter in size.
The study shows "a pronounced neurovascular dissociation that occurs immediately after small-scale strokes, becomes the most severe a few days after, lasts into chronic periods and varies with the level of ischemia," the researchers wrote.
The study in rodent models revealed the restoration of blood flow in the brain occurs first, followed by restoration of neuronal electrical activity. They observed that neuronal recovery could take weeks even for small strokes, and possibly longer for larger strokes.
The study required implants and instrumentation designed to monitor both blood flow and brain activity simultaneously before, during and after the onset of strokes.
"This started with the device," said the senior author, who developed a flexible neural electrode. "That was my transition from being trained as a material physicist to neuroengineering.
"As soon as we had the electrodes, I wanted to use them to understand brain functions and dysfunctions in a domain that was difficult to probe with previous technology," the senior author said. "The electrodes are extremely flexible and well suited to be combined with optical imaging in exactly the same brain regions."
The electrodes were combined with optical lines able to measure blood flow by recording laser speckle patterns. The combined data, gathered for as long as eight weeks, gave the researchers an accurate comparison between blood flow and electrical activity.
"The strokes we focus on are so small that when they happen, it's very hard to detect them from behavioral measures," the author said. "We would not easily see impairment in animal locomotion,
"The implications in humans are similar," the author said. "These microinfarcts can occur spontaneously, especially in aged populations. Because they're so tiny, it's not like you're having a stroke. You will not notice it at all. But it has been long hypothesized that it's related to vascular dementia."
While the study would be hard to replicate in humans, the implications could improve diagnoses of patients who suffer microinfarcts.
"There are a lot of similarities in neurovascular coupling in rodent models and in humans," the author said. "What we observed in rodents likely has a similar signature in humans, and I hope that can be of use to clinicians."
"We're interested in knowing not just how a single microinfarct would alter neural activity but also, cumulatively, whether the effect of multiple microinfarcts that occur at different times would be stronger or weaker than the sum of the individuals," the author said.
Blood flow recovers faster than brain in micro strokes
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