Since humans learned to speak, they have put their words into two basic categories, nouns and verbs. Nouns denote objects; verbs refer to actions. Dictionaries of specialized words have been added by bankers, lawyers, scientists, and clergy, but this core distinction remains.
Birds sing, but sings don’t bird, in any language.
Scientists would really like to know how our brain arranges words into meaningful sentences, how it does grammar. “Knowing this would help us understand how the brain organizes knowledge,” says Alfonso Caramazza, Daniel and Amy Starch Professor of Psychology at Harvard University.
Caramazza is one of many people who look for clues to this organization in brain-damaged people. Those with injuries in certain areas under the left temple often show difficulties producing nouns. Others who suffered trauma on the front left side of the brain may struggle with verbs. He describes one case of an injury to the front left side that resulted in such a deficit. Closer examination revealed a small area of the brain that was not getting enough blood. When the medical team restored blood flow, that patient regained the ability to produce and comprehend verbs.
Working with Kevin Shapiro, an M.D.-Ph.D. graduate student, Caramazza is trying to pinpoint the difficulties such patients face when processing nouns and verbs. For example, some of them find it tough to use these words in a sentence. They can say “the sails” but not “he sails.”
With the assistance of Lauren Moo at the Harvard Medical School, Caramazza used an MRI brain scanner at Massachusetts General Hospital in Boston to obtain images of brain activity while volunteers spoke short phrases and sentences. Other researchers have done such scanning experiments, but this is the first time that specific brain sites were seen to be activated by either nouns or verbs, but not both.
“For the first time we were able to identify areas of the brain where no overlap occurs between production of nouns and verbs,” Caramazza maintains.
The experiments were described in the online edition of the Proceedings of the National Academy of Science (http://www.pnas.org) on Jan. 16.
Wugs and zibs
Five men and five women said things like “many doors” or “he weeps,” with their heads in an MRI scanner that shows which areas of the brain are most active at the time. Their ages ranged from 19 to 25 years, all of them healthy, native English speakers. Eighteen others, all Harvard students, did the same tasks outside the scanner for comparison purposes. All were right-handers, people whose language ability is predominantly on the left side of their brains. Lefties can be left, right, or mixed.
In addition to ordinary words describing real objects and actions, the subjects spoke nonwords in sentences such as “he zibs” or “the wugs.” That didn’t fool their brains. Their gray matter treated “zibs” as a verb and “wugs” as a noun.
In other experiments, the subjects produced both concrete and abstract nouns and verbs (“head” and “idea,” “run” and “enjoy”). Then they went through plurals, tenses, and irregular forms like “sit” and “sat,” “play” and “played,” “goose” and “geese.” That didn’t change the brain areas that were activated by either nouns or verbs but not both.
“If the same brain areas keep responding in the same way, it suggests that we have found the core areas where these basic parts of speech are represented,” notes Caramazza.
Of course, this is only a beginning for understanding how sentences get from your brain to your mouth. Other nearby brain circuits are needed to handle plurals, tenses, and irregular forms and to make sure “sings don’t bird” and people don’t “sitted” down. These areas can and do handle both nouns and verbs, including such things as nouns used as verbs like “kiss me,” or “he bugs me.”
At a loss for words
Eventually, such understanding should help people who lose their ability to speak or comprehend words as a result of brain damage. If a person becomes noun- or verb-impaired, surgeons and other specialists now know where to look for a solution. As the whole circuitry involved in producing sensible sentences is unveiled by research, techniques may be developed to treat linguistic blocks between what people intend to say and what they can say.
Once all the areas that hold nouns and verbs and get them into your mouth are fully mapped, they can guide surgeons who must work in those sensitive neighborhoods. Caramazza uses the example of surgery to reduce epileptic seizures. During such delicate work, surgeons need to know what areas to avoid with their scalpels.
Caramazza admits that such applications are far down the road, but they are things that he says add “impetus” to his research. For now, however, he can enjoy the knowledge of making a big contribution to solving a very old linguistic mystery.