A single, tiny stroke can cause brain damage and lead to changed behavior or even disability, says a new study.

Researchers from University of California, San Diego have found that blocking a single blood vessel in the brain can cause tissue damage. However, a drug already in use can slow down these changes and reduce the risk of early on-set of dementia.

Researchers used laser light to clot blood at definite points in the blood vessels that go from surface of the brain towards the neural tissue of rats.

When they looked at the brains after a week, they saw that the parts of brain were damaged in a way that was similar to brain damage seen in people with dementia. These tiny lesions are extremely difficult to see with a conventional MRI scan.

"It's controversial whether that sort of damage has consequences, although the tide of evidence has been growing as human diagnostics improve," said David Kleinfeld, professor of physics and neurobiology, lead author of the study.

esearchers wanted to see if the changes in brain affected the rats' behavior. To test this, researchers trained thirsty rats to jump from one platform to another to get water in the dark.

The rats jump to the second platform if they could feel the platform with a paw or a snout, or even with their whiskers. Many rats can be trained to rely on a single whisker (when others are clipped) to judge the distance of the platform. Rats don't jump to the next platform if they don't feel the next platform.

"The whiskers line up in rows and each one is linked to a specific spot in the brain. By training them to use just one whisker, we were able to distill a behavior down to a very small part of the brain," Andy Y. Shih, lead author of the paper.

When researchers blocked single microvessels that fed a column of brain cells that respond to signals received from the remaining whisker, the rats still crossed to the far platform when the gap was small.

However, the rats quit jumping when the platform was beyond the reach of their snout.

When rats were given FDA-approved drug memantine, they jumped the whisker wide gaps and their brains showed fewer signs of brain damage.

"This data shows us, for the first time, that even a tiny stroke can lead to disability. I am afraid that tiny strokes in our patients contribute-over the long term-to illness such as dementia and Alzheimer's disease," said Patrick D. Lyden, a co-author of the study and chair of the department of neurology at Cedars-Sinai Medical Center in Los Angeles.

The study is published in the journal Nature Neuroscience.