Narrator: 100 years ago, scientists believe language depended on two key areas in the left hemisphere— a region behind the ear, identified by a German doctor, Carl Wernicke, seemed to be responsible for overall meaning. It handled word selection and sentence construction. An area further forward, found by a French doctor, Paul Broca, was thought to control the last stage of generating the speech sounds. Since then, a far more complex picture has emerged.

Wilson Talley: (on tape) Ladies and gentlemen, I'm pleased to participate in this evening's discussion of health considerations in the development of energy sources. These considerations have been with us for some time—

Narrator: Dr. Wilson Talley, award-winning nuclear physicist, scientific advisor to the American government, will never be able to speak like this again, because he suffered a stroke.

Wilson Talley: (on tape) Only with the advent of nuclear energy—

Wilson Talley: Much, very nice. That's March 1998, the stroke. March 6. Sleep. And right here, about 2:00 PM, I got up. The bathroom was here. And when— and found out this, and very strange.

Nina Dronkers: Dr. Talley has a great deal of difficulty understanding anything that's said to him or even things that he reads. And he also has a great deal of difficulty in producing language. Now what happens when he tries to talk is that the words come out very fluently, but what he says doesn't have a lot of content to it. He has difficulty in finding the words that he wants, and he has a great deal of difficulty also in producing sentences that are coherent, that really reflect what it is he wants to say.

Narrator: A brain scan revealed that a hemorrhage had destroyed large parts of Wilson's left hemisphere, including the whole of Wernicke's area.

Nina Dronkers has assembled a unique collection of brain scans of stroke patients with language disorders. It turns out that many have indeed damaged the two classic language areas. But the broader picture reveals a network of many different brain areas which handle specific aspects of language.

Nina Dronkers: We've seen that there are certain patients who have a great deal of trouble really just naming things. We've found patients who have difficulty understanding the grammatical rules of language. All of those different kinds of patterns tell us, first of all, that the process of language is incredibly complex. And also that there must be many different brain areas that subserve each and every one of those different functions.

Computer: Touch the white circle.

Wilson Talley: Circle?

Narrator: Patients often seem to recover some of the basic aspects of language, like the ability to recognize word sounds, which suggests that these functions don't require their own specialized brain structures.

Computer: Touch the green square.

Wilson Talley: Green, green.

Nina Dronkers: Unfortunately, we rarely see complete, total recovery in our aphasic patients.

Man: Excellent.

Wilson Talley: Thank you.

Nina Dronkers: And the fact is that, in most of them, a fairly significant amount of brain has been affected by their injuries, and that it is difficult for other brain areas that have, for such a long period of time, been doing something else to suddenly take on this new function. And what we think happens is that the remaining brain areas try to take on this task of language, but they do it in their own way. But unfortunately, they're not as good at it as those left hemisphere language mechanisms, because they haven't been doing that all of those years.