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Thursday May 28, 1998 NEW YORK (Reuters) -- An extraordinary experiment using electrodes implanted on the surface of the brain of a conscious patient allowed a team of neurosurgeons, neuropsychologists, and cognitive scientists to directly measure the speed of language processing and object comprehension. The patient, a 22-year-old student fluent in both English and Farsi, had 174 platinum electrodes implanted in his cortex in preparation for surgery to cure chronic, severe epilepsy. The electrodes are normally used to identify the exact region of the brain that must be removed to control seizure activity. This patient volunteered to undergo a series of linguistic tests with the electrodes in place. He was asked to name and categorize various objects, words and pictures while the electrodes recorded the electrical activity of his brain. The researchers, led by neurologist Dr. John Hart, of Johns Hopkins University, Baltimore, Maryland, found that an area of the brain called the left occipitotemporal gyrus became active about 300 milliseconds after the patient saw the picture or object. Some of the same tests were then repeated while the investigators passed a small electrical current through a few of the electrodes. The current disabled tiny portions of the patient's brain for a fraction of a second at a time. If the team applied current to the occipitotemporal gyrus, located near the rear base of the brain, the patient experienced difficulty speaking normally. He had trouble finding words, and his speech became garbled. Hart describes the patient's errors in an accompanying press release: "Applying current (in the gyrus) as we presented the patient with a new test could cause problems in understanding what objects are; misinterpretations of verbs, colors or shapes; and word-finding difficulties in spontaneous speech." If the current was applied at the same time or up to 400 milliseconds after a picture was shown to him, he could not name the object before him. But if electrical current was delayed until at least one second after he saw the picture, he had no trouble naming the object. The researchers report their results in the May 25th issue of the Proceedings of the National Academy of Sciences. They conclude from these experiments that the patient's speech processing begins about 300 milliseconds after he sees an object, and ends before a second has elapsed. Familiar objects take about 450 milliseconds to process, but unfamiliar objects can take up to 750 milliseconds to comprehend. The results imply that important aspects of recognition and comprehension can be localized to one area in the brain, and give support to the theory that language comprehension processing has a single, discrete system in the brain. The time course also leads the authors to suggest that "information accumulates gradually, rather than in a strictly all-or-none fashion." SOURCE: Proceedings of the National Academy of Sciences 1998;95:498-6503. -- Judith Richards, London, Ontario, Canada [log in to unmask]