Thanks to an unusual opportunity to implant electrodes into the brains of alert adults, researchers have described the sequence and timing of distinct steps in language processing to a finer degree than previous methods have allowed.

The brain's language center, named Broca's area after the French physician Pierre Paul Broca who discovered it in 1865, has remained a relative black box since its recognition.

Unlike other brain-based functions, such as movement or vision, there are no animal models for language study—formal language being a uniquely human skill. So observing how the brain rapidly recognizes and produces words has been challenging for even contemporary scientists who have to rely largely on comparatively imprecise techniques, such as functional magnetic resonance imaging (fMRI) or lesion studies.

Researchers got a break, however, in the form of patients in line for surgical treatment for epilepsy. As part of preparation for their surgery, three adults had electrodes implanted in Broca's area and anterior temporal cortex to allow doctors to pinpoint which areas of the brain would be best to remove. During the procedure, known as intracranial electrophysiology, researchers asked the patients to silently sound-out words they saw on a screen and to fill in the missing verb in the proper tense or the proper form of a missing noun. Meanwhile, the researchers were recording the local electric field potentials from the wired areas of subjects' brains to the nearest millisecond—and millimeter.

After studying the readouts, the researchers found that in these normally reading adults, word identification, grammar and pronunciation all activated parts of Broca's area—and in a very neatly defined sequence. Like clockwork, it took about 200 milliseconds to identify a word, 320 milliseconds for grammatical composition and 450 milliseconds for phonological encoding.

The results of the research, which was led by Ned Sahin, a postdoctoral fellow at the University of California, San Diego's Department of Radiology and Harvard University's Department of Psychology, were published online Thursday in the journal Science.

"Sahin et al. demonstrate, by recording neuronal activity in the human brain, that different kinds of linguistic information are indeed sequentially processed within Broca's area," Peter Hagoort and Willem Levelt, both of the Max Plank Institute for Psycholinguistics in the Netherlands, wrote in a commentary in the same issue of Science accompanying the paper.

Previous studies had shown that the brain takes about 600 milliseconds to form vocal speech. So the speed with which each of these processes occurred was not as big of a surprise to Sahin and his colleagues as the fact that these three distinct tasks were done separately, in a tightly timed sequence, and within millimeters of each other in the brain.

Another curious finding was that, unlike in other studies that have shown nouns and verbs to be understood and formulated differently, the electrode work showed the two parts of speech to be processed in much the same way.

"It was striking that where we looked we only saw similarities—of time, amplitude and shape of the wave," Sahin says about the electrical signals recorded during processing of nouns and verbs. He notes that their data doesn't presume to overturn previous findings, but "there seems to be something that we've tapped into that are shared between the two categories. We've found a process dealing with the morphology and structure of words—as well as their identity and how to pronounce them—that cuts across two very different categories of words."

The electrical readouts also help to dispel the theory that another part of the brain, Wernicke's area, is primarily responsible for reading and hearing language. Their data show that, in fact, Broca's area also activated during the reading and identification phases. These findings, "indicate that the role of Broca's area…should be characterized in more general terms," Hagoort and Levelt wrote.

Even though opportunities for this procedure are infrequent, Sahin and his team plan to use it again in the future to look more broadly at the full brain's involvement in language: "Everything from when the person first sees the word—the visual parts of the brain—to the motor parts" [is] involved in speech, he says.

Despite the new findings, a lot remains to be discovered about Broca's area and language processing in general, Sahin says. "The area of the brain in question has been under intense study for over 150 years, but we still don't know what it does," Sahin notes, adding: "We don't have the whole picture, [but] it helps us understand how language is processed in the brain."