Learning or speaking multiple languages exercises your brain, helping you process information in a more efficient way, and that's true no matter what age you are, researchers say.

That's because the brain of a bilingual person is constantly referencing both languages and then choosing which language to utilize and which to ignore in processing any information, a study at Northwestern University found.

This constant brain "exercise" keeps the brain nimble so it doesn't need to work so hard in performing cognitive tasks, they report in the journal Brain and Language.

"It's like a stop light," says lead study author Viorica Marian, a professor of communication science and disorder. "Bilinguals are always giving the green light to one language and red to another. When you have to do that all the time, you get really good at inhibiting the words you don't need."

In the study, the researchers used MRI scans to observe the phenomena of co-activation and inhibition in bilingual participants.

Co-activation in bilingual comprehension means fluent bilinguals can have both their languages "active" simultaneously, whether they are consciously using them or not.

Inhibition is the ability to select the correct language for the cognitive task at hand despite competition by the other language.

In the study, participants heard a spoken word -- for instance, "cloud" -- and were then shown four pictures, including one displaying a cloud and another picture evoking a similar-sounding word, such as "clown."

The participants had to indicate the correct picture and ignore the one of a similar-sounding word.

Because the brains of bilingual people are more comfortable with controlling two languages and inhibiting the irrelevant words, there proved better at filtering out the competing words, the researchers found.

"Inhibitory control is a hallmark of cognition," Marian says. "Whether we're driving or performing surgery, it's important to focus on what really matters and ignore what doesn't."

The benefit of bilingualism holds for people of all ages, she suggests, and may explain why bilingualism can apparently provide a protective advantage against Alzheimer's and dementia.

"That's the exciting part," she says. "Using another language provides the brain built-in exercise. You don't have to go out of your way to do a puzzle because the brain is already constantly juggling two languages."

So instead of Sudoku, consider becoming a polyglot, she suggests.

"It's never too late to learn another language," she adds. "The benefits can be seen even after just one semester of studying."

"Even minimal knowledge of a second language is advantageous."