TORONTO -- An experimental procedure that stimulates the brain with electrical pulses through the skull may help people recover the ability to speak after suffering a stroke, researchers say.

Up to 30 per cent of stroke survivors are left with a condition called aphasia, in which they have difficulty understanding language, speaking, reading or writing.

In a small study, Canadian and German researchers tested the effects of transcranial magnetic stimulation, or TMS, on patients recovering from a stroke but left with different degrees of aphasia caused by the damage to their brains.

Twenty-four stroke patients were enrolled in the trial, with 13 getting TMS and 11 treated with a sham procedure. Following the sessions, participants were immediately given speech language therapy.

Patients received 20 minutes of TMS or sham stimulation followed by 45 minutes of speech and language therapy for 10 days, the authors report in the American Heart Association journal Stroke.

"Those who received the real treatment recovered better from their aphasia than those who received the sham treatment," said lead author Dr. Alexander Thiel, director of the stroke unit at Jewish General Hospital in Montreal.

Improvements in the TMS-treated group were about two to three times greater than in the sham-treatment group, he said Thursday from Montreal.

"Even those who received the sham treatment, they also improved, but they didn't improve as much as the others."

There are different types of aphasia, said Thiel, who worked with colleagues at the Max Planck Institute for neurological research in Cologne, Germany, where he worked before coming to Canada.

"The most common one is expressive aphasia, so they have difficulty formulating full sentences, difficulties getting correct words out or that they want to tell you something and they know exactly what they want to tell but they can't get the words out.

"And that, of course, is very frustrating."

TMS is a non-invasive procedure, in which a handheld magnetic coil is applied to the skull, lining up over a specific area on one side of the brain. The device delivers a low-intensity electrical current which causes muscles to contract, creating a "tingling, twitching" feeling in the scalp.

The device is applied to the side of skull where the brain has not been affected by the stroke -- in this case on the right side.

"So we try to shut down the unaffected hemisphere so all the therapeutic effort would go to the affected hemisphere," said Thiel, explaining that the effects of TMS last about 30 to 45 minutes, during which time patients undergo speech-language therapy.

The idea is to shut down the right side to force the weakened left side of the brain -- particularly the areas involved in speech -- to do all the work of relearning language, he said. The mental exercise also may prompt the brain to form new connections, a phenomenon known as neuroplasticity.

"We want to re-activate what's there in the left hemisphere, make it work," he said. "This is similar to physical rehabilitation where the unaffected limb is immobilized with a splint so that the patient must use the affected limb during the therapy session."

Researchers also tested writing and reading ability.

"We saw some effect on writing, some improvement, but the main improvement was really in naming objects," Thiel said. "And this is very important because if you can't speak, the first thing you start with or a little child starts with, it points at things and names them."

Not all stroke survivors with aphasia could be treated with the electrical stimulation technique. People who have seizures or wear a pacemaker would not be candidates, and anyone with complete speech loss would likely not benefit, he pointed out.

The small trial is a proof-of-concept study, which shows TMS was safe for patients and appeared to have benefit in overcoming aphasia more quickly. But more research is needed to definitively prove its effectiveness, Thiel stressed.

In October, the scientists will begin an international, multicentred trial of TMS with about 100 stroke patients. Dubbed NORTHSTAR, the study will include three Canadian centres -- two in Montreal and one in Toronto.

The researchers want to get patients into the study as early as possible following a stroke, ideally about a month after the event. That's because genes that kick into gear to form new connections in the brain peak about two to three weeks after a stroke, he said.

"We think that there is a window of opportunity where these kinds of therapies are especially effective."