"The bilinguals, we found, manifested a cognitive system with the ability to attend to important information and ignore the less important.
Q. How does this work — do you understand it?
A. Yes. There’s a system in your brain, the executive control system. It’s a general manager. Its job is to keep you focused on what is relevant, while ignoring distractions. It’s what makes it possible for you to hold two different things in your mind at one time and switch between them.
If you have two languages and you use them regularly, the way the brain’s networks work is that every time you speak, both languages pop up and the executive control system has to sort through everything and attend to what’s relevant in the moment. Therefore the bilinguals use that system more, and it’s that regular use that makes that system more efficient.
Q. One of your most startling recent findings is that bilingualism helps forestall the symptoms of Alzheimer’s disease. How did you come to learn this?
A. We did two kinds of studies. In the first, published in 2004, we found that normally aging bilinguals had better cognitive functioning than normally aging monolinguals. Bilingual older adults performed better than monolingual older adults on executive control tasks. That was very impressive because it didn’t have to be that way. It could have turned out that everybody just lost function equally as they got older.
That evidence made us look at people who didn’t have normal cognitive function. In our next studies , we looked at the medical records of 400 Alzheimer’s patients. On average, the bilinguals showed Alzheimer’s symptoms five or six years later than those who spoke only one language. This didn’t mean that the bilinguals didn’t have Alzheimer’s. It meant that as the disease took root in their brains, they were able to continue functioning at a higher level. They could cope with the disease for longer.
Executive control is affected in MS as well. Being bilingual might prolong time to cognitive disability in MS as it does in Alzheimer's.