Mini-strokes are thought to be fairly fleeting, often lasting a few minutes with symptoms gone within 24 hours and no apparent lingering effects -- although they do heighten a person's risk of full-blown stroke in the future.

They're transient, as one might infer from their formal name, transient ischemic attack. They've come and gone.

But experiments conducted at a neuroscience lab in British Columbia paint a picture of a more lasting effect.

Researchers used transcranial magnetic stimulation to examine patterns of brain activity in 13 patients who had experienced TIAs 14 to 30 days earlier, and compared them to the brain activity of 13 healthy people.

Lara Boyd, a neuroscientist with the Brain Research Centre at Vancouver Coastal Health Research Institute and the University of British Columbia, said magnetic resonance imaging might or might not reveal a little damaged area or lesion in the brain after a TIA.

"But we wondered if we could maybe detect something with neurophysiology, with electro-physiology, that has previously gone unnoticed," she said in an interview.

The non-invasive method involves putting a pulse of electrical current into the brain; for example, it allows scientists to measure how much current is needed to cause a motor response, such as a muscle twitch.

"By using some variations on this particular approach, we can then gauge how excitable the brain is," Boyd said.

It's already known that after a stroke, the stroke side of the brain is not very excitable because damage causes it to be suppressed or depressed, she said.

And now, the B.C. lab has found essentially the same thing in patients who have had a TIA.

"They're now supposedly recovered two weeks after that event. We still see the same pattern, or similar pattern, of suppression of the damaged side of the brain," Boyd said.

"So it's indicating to us that something is seriously wrong in that part of the brain, that this event was not transient. We see this kind of lasting effect in the ability to excite the side of the brain that was hurt by the TIA."

The research was published Thursday in Stroke, the journal of the American Heart Association.

Boyd said a longitudinal study of 60 people will come next, to examine TIA patients in the emergency department, at 14 days, 30 days and 60 days to see if this changes over time.

"And then our real main question is, 'Could this be a useful tool in predicting who's at most risk for going on and having a full-blown stroke?"'

It's also hoped that the technique can help discern whether someone is having a TIA or a migraine, which sometimes has similar symptoms.

Boyd said a TIA is a serious medical event, and there is approximately a 20 per cent risk of going on to have a full-blown stroke within the next 60 days.

"It's causing lasting change in your brain and you should definitely take it seriously and seek medical attention," she advised.

"What's actually incredibly common is that someone has these symptoms -- sudden motor weakness or change in vision or loss of sensation -- but after an hour or two it gets better. And so they think, 'Well, I don't want to bother my physician, I'm really busy, I don't have time to go to emerg,' and they don't follow it up."

Dr. David Spence, director of the Stroke Prevention & Atherosclerosis Research Centre at the Robarts Research Institute in London, Ont., said the study's findings are interesting but not surprising.

It won't change the approach to managing TIAs since they are already regarded as serious matters requiring investigation and urgent treatment, he said in an email.

"What I think it will more likely change is investigation into loss of cognitive function: if TIAs cause brain damage, they should increase the risk of cognitive decline," wrote Spence, who is also a professor at the University of Western Ontario.