You may have heard it before: being bilingual can help ward off dementia. Now, a new study offers the brain scans to back up those findings.

A number of studies in recent years have shown that knowing more than one language and speaking them regularly can delay the onset of dementia. Those studies reached their conclusions by looking at bilingual and monolingual seniors and then noting the age at which the patients began to decline cognitively with memory problems, attention problems and difficulty with planning and organization.

This new study from Toronto researchers included CT (computed tomography) brain scans of patients who had been diagnosed with probable Alzheimer's disease and who had similar levels of education and cognitive skills.

The team found that the scans of the bilingual patients showed twice as much damage in areas of the brain known to be affected by Alzheimer's. And yet, cognitively, these patients were doing as well as their monolingual counterparts.

The finding suggests that being bilingual somehow preserves cognitive function, even with areas of the brain being destroyed by disease, says Dr. Tom Schweizer, a neuroscientist at St. Michael's Hospital who led the study.

"What we noticed was that in the areas associated with Alzheimer's pathology -- so that's the temporal cortex, which is the area of the brain that serves memory function -- we noticed that the bilingual patients had twice as much atrophy in those areas than the monolingual patients," Schweizer explained to CTV's Canada AM.

"That's interesting because, despite the extra disease burden in the bilingual patients, they maintained their level of cognitive performance as well as monolingual patients."

The study, which appears in the journal Cortex, was small, involving just 40 patients, half of whom were fluent in another language. But it's being called the first to provide physical evidence to confirm the previous research on the topic.

While it should stand to reason that brains that look more damaged would perform worse on thinking tests, Schweizer theorizes that being bilingual somehow protects the brain, boosting its "cognitive reserve" and resilience to damage.

It's still unclear how being bilingual protects the brain. Schweizer says it could be that bilingual people who are constantly switching from one language to another are exercising their brain without even realizing it.

"We think it's enhancing neural networks in the brain; it's actually making the brain a little more efficient and so it can probably compensate for any type of disease process," he explained.

The study authors say that while being bilingual might delay the onset of dementia symptoms, bilingualism can't prevent dementia.

But they say more study is needed to determine whether, once dementia symptoms appear, the disease progresses faster in bilingual people than monolingual patients.

They'd also like to know whether a second language has to be learned early in life to provide the most benefit.

The team would like to repeat the study in a larger sample of patients, using more sophisticated MRIs, which do a better job of noting brain damage.

The concept that one can build up "cognitive reserve" is one of the reason that why many physicians encourage older people to do brain work, like crossword or Sudoku puzzles, says Schweizer.

"You may not want to pick up another language; you may want to learn a musical instrument -- anything to exercise the brain and keep it active in your retirement years, and hopefully before that so you can keep that ball rolling."