The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

I then asked Dr. Hamdi to sing “Happy Birthday.” He sang it effortlessly. Not only could he carry the tune well, but all the words were there and correctly pronounced. This was in stark contrast to his speech, which, in addition to missing important connecting words and lacking phrase structure, also contained mispronounced words and lacked the intonation, rhythm, and the melodious flow of normal speech. If his problem were poor control of his vocal apparatus, he shouldn’t have been able to sing, either. To this day we don’t know why Broca’s patients can sing. One possibility is that language function is based mainly in the left hemisphere, which is damaged in these patients, whereas singing is done by the right hemisphere.

We had already learned a great deal after just a few minutes of testing. Dr. Hamdi’s problems with expressing himself were not caused by a partial paralysis or weakness of his mouth and tongue. He had a disorder of language, not of speech, and the two are radically different. A parrot can talk—it has speech, you might say—but it doesn’t have language.

HUMAN LANGUAGE SEEMS so complex, multidimensional, and richly evocative that one is tempted to think that almost the entire brain, or large chunks of it at least, must be involved. After all, even the utterance of a single word like “rose” evokes a whole host of associations and emotions: the first rose you ever got, the fragrance, rose gardens you were promised, rosy lips and cheeks, thorns, rose-colored glasses, and so on. Doesn’t this imply that many far-flung regions of the brain must cooperate to generate the concept of a rose? Surely the word is just the handle, or focus, around which swirls a halo of associations, meanings, and memories.

There’s probably some truth to this, but the evidence from aphasics such as Dr. Hamdi suggests the very opposite—that the brain has neural circuits specialized for language. Indeed, it may even be that separate components or stages of language processing are dealt with by different parts of the brain, although we should really think of them as parts of one large interconnected system. We are accustomed to thinking of language as a single function, but this is an illusion. Vision feels like a unitary faculty to us as well, yet as noted in Chapter 2, seeing relies on numerous quasi-independent areas. Language is similar. A sentence, loosely speaking, has three distinct components, which are normally so closely interwoven that they don’t feel separate. First, there are the building blocks we call words (lexicon) that denote objects, actions, and events. Second, there is the actual meaning (semantics) conveyed by the sentence. And third, there is syntactic structure (loosely speaking, grammar), which involves the use of function words and recursion. The rules of syntax generate the complex hierarchical phrase structure of human language, which at its core allows the unambiguous communication of fine nuances of meaning and intention.

Human beings are the only creatures to have true language. Even chimps, who can be trained to sign simple sentences like “Give me fruit,” can’t come close to complex sentences such as “It’s true that Joe is the big alpha male, but he’s starting to get old and lazy, so don’t worry about what he might do unless he seems to be in an especially nasty mood.” The seemingly infinite flexibility and open-endedness of our language is one of the hallmarks of the human species. In ordinary speech, meaning and syntactic structure are so closely intertwined that it’s hard to believe that they are really distinct. But you can have a perfectly grammatical sentence that is meaningless gibberish, as in the linguist Noam Chomsky’s famous example, “Colorless green ideas sleep furiously.” Conversely, a meaningful idea can be conveyed adequately by a nongrammatical sentence, as Dr. Hamdi has shown us. (“It’s difficult, ummm, left side perfectly okay.”)

It turns out that different parts of the brain are specialized for these three different aspects of language: lexicon, semantics, and syntax. But the agreement among researchers ends there. The degree of specialization is hotly debated. Language, more than any other topic, tends to polarize academics. I don’t quite know why, but fortunately it isn’t my field. In any case, by most accounts Broca’s area seems mainly concerned with syntactic structure. So Dr. Hamdi had no better chance than a chimp of generating long sentences full of hypotheticals and subordinate clauses. Yet he had no difficulty in communicating his ideas by just stringing words together in approximately the right order, like Tarzan. (Or surfer dudes in California.)