New York, Jan 17 (IANS): Although mini-strokes may seem to last only for a few minutes, the effect may be long lasting and is likely to contribute to dementia, research have suggested.

Mini-strokes or "transient ischemic attack" (TIA) is a brief stroke-like attack that occurs when there is a temporary drop in the blood supply to the brain.

Mini-strokes -- also called cortical microinfarcts -- cause minuscule lesions of approximately 0.05-3 millimetres in diameter.

However, the findings showed that a mini-stroke can create a dysfunction in the brain that could be as large as 12 times than what was visible by histology or magnetic resonance imaging (MRI).

The functional deficit caused by a single microinfarct occurs across a much larger area of viable peri-lesional tissue than was previously understood and the resulting deficits are much longer-lasting.

The neuronal activity across the affected tissue area was found to remain partially depressed for 14 to 17 days after the microinfarct.

"Even after three weeks, the neurally evoked blood flow responses had only partially recovered. So, that 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," said Andy Shih, Assistant Professor at the Medical University of South Carolina in the US.

Furthermore, these tiny infarcts occur not only in the brain's grey matter, but also in the white matter, which sends messages from one part of the brain to another.

"Over time, after you have a lot of microinfarcts, there may be enough accumulated damage in the brain's circuitry to equal the impact of a larger event," Shih said.

For the study, the team developed a mouse model so that they could examine the effects of individual cortical microinfarcts on surrounding tissue function in vivo over several weeks post-event.