PESHAWAR: Mini-strokes are a type of stroke that only last for a few minutes. A new research suggests that the effect of a mini-stroke is more serious than previously thought. The team was led by Andy Shih, PhD, an assistant professor of neurosciences at MUSC, and the findings were published in the Journal of Cerebral Blood Flow and Metabolism. Shih and the team designed a mouse model so that they could study the effects of individual microinfarcts on the cortical tissue over several weeks following the ministroke. The barrel cortex is part of the somatosensory cortex of mice, marsupials, and other rodents, and it has a specific structure that mirrors the whiskers on the snout. For this experiment, researchers implanted cranial windows in the barrel cortex, and then compared functional readouts of brain activity with the location of the mini-stroke core. They performed both in vivo and post-mortem brain analyses. The team used c-Fos expression and in vivo, two-photon imaging of single vessel hemodynamic responses in order to measure the precise scale of sensory-evoked neural activity. The post-mortem c-Fos immunostaining showed that the mini-stroke had affected an area 12 times greater in volume than the microinfarct core. Additionally, the single vessel two-photon imaging revealed that the neuronal activity across this affected area was depressed for 14-17 days after the mini-stroke. The results were deemed “surprising” by the researchers. Andy Shih said that “I knew larger strokes could have distant effects, but I was surprised that something of this scale could have such a large effect. The MRI signal increased and then went away as we had expected, but we were surprised on autopsy to see that there was still lots going on – tissue damage and neuro inflammation. Even after 3 weeks, the neurally evoked blood flow responses had only partially recovered. This means a microinfarct can come and go and you can see it briefly with MRI but it leaves a lasting impression on brain function — possibly for months.” Shih explains the significance of the study both in terms of the methodology typically used to assess the impact of mini-strokes, and the implications for preventive care. “These infarcts are so small and unpredictable, we just have not had good tools to detect them while the person was still alive,” he says. “Until now, we just had post-mortem snapshots of these infarcts at the end of the dementia battle as well as measures of the person’s cognitive decline, which might have been taken years before the brain became available for study.” Most mini-strokes are difficult to detect with conventional neuroimaging techniques, as often the in vivo data does not match the post-mortem histological evidence. This makes it difficult for researchers to connect the mini-strokes with the development of cognitive decline over time. However, the research conducted by Shih and the team bypassed these difficulties by creating a model allowing them to follow the effects of individual cortical mini-strokes over several weeks. Furthermore, Shih suggests that the findings might also shape future preventive practices. Given that microinfarcts have such a long-lasting impact over a wide area, several microinfarcts may cause “enough accumulated damage in the brain’s circuitry to equal the impact of a larger event. On a clinical level, maybe therapeutics can play a bigger role. Maybe drugs that we already have can mitigate the cumulative damage of microinfarcts If an MRI shows a person is at high risk for microinfarcts, maybe one day we can put them on a drug for a while to reduce the impacts of these lesions.”