Electrical Stimulation

Electrical stimulation of the brain in awake subjects undergoing neurosurgery was introduced in the 1930s by Wilder Penfield and colleagues at the Montreal Neurological Institute. Penfield treated patients with focal brain lesions, operating to remove damaged tissue. In doing so, Penfield performed intraoperative electrical stimulation mapping to identify areas of the cortex whose loss would be debilitating. Of relevance to this article, Penfield mapped language-related brain areas, compiling data from scores of cases to produce functional maps of language areas, including Broca's area. (The reader is encouraged to investigate the numerous journal articles and books published by Penfield and colleagues.) Today, the most prolific applicants of Penfield's intraoperative cortical mapping technique are George Ojemann and colleagues at the University of Washington. In a classic, 1982 review of his cases, Ojemann reported on more than 100 patients, indicating that the location and extent of Broca's area (and other language areas) are more complex and variable than previously thought, at least in a population of persons with chronic brain lesions. The technique of electrical stimulation mapping of the cortex allowed the study of language areas, and Broca's area in particular, to expand into testing the use of normal tissue in specific locations in conscious patients rather than simply documenting the effects of damage to areas of the cortex. Electrical stimulation mapping has emphasized the individual variability of language areas of the brain in clinical populations, and recent work seems to show that the classically defined Broca's area may not be necessary for speech processing. The works of Penfield and Ojemann have made a major contribution to the knowledge of the location and functions of Broca's area.

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