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.

Q. So high school French is useful for something other than ordering a special meal in a restaurant?

A. Sorry, no. You have to use both languages all the time. You won’t get the bilingual benefit from occasional use.

Q. One would think bilingualism might help with multitasking — does it?

A. Yes, multitasking is one of the things the executive control system handles. We wondered, “Are bilinguals better at multitasking?” So we put monolinguals and bilinguals into a driving simulator. Through headphones, we gave them extra tasks to do — as if they were driving and talking on cellphones. We then measured how much worse their driving got. Now, everybody’s driving got worse. But the bilinguals, their driving didn’t drop as much. Because adding on another task while trying to concentrate on a driving problem, that’s what bilingualism gives you — though I wouldn’t advise doing this.

Q. Has the development of new neuroimaging technologies changed your work?

A. Tremendously. It used to be that we could only see what parts of the brain lit up when our subjects performed different tasks. Now, with the new technologies, we can see how all the brain structures work in accord with each other.

In terms of monolinguals and bilinguals, the big thing that we have found is that the connections are different. So we have monolinguals solving a problem, and they use X systems, but when bilinguals solve the same problem, they use others. One of the things we’ve seen is that on certain kinds of even nonverbal tests, bilingual people are faster. Why? Well, when we look in their brains through neuroimaging, it appears like they’re using a different kind of a network that might include language centers to solve a completely nonverbal problem. Their whole brain appears to rewire because of bilingualism.