Cortical language localization in left, dominant hemisphere

An electrical stimulation mapping investigation in 117 patients

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✓ The localization of cortical sites essential for language was assessed by stimulation mapping in the left, dominant hemispheres of 117 patients. Sites were related to language when stimulation at a current below the threshold for afterdischarge evoked repeated statistically significant errors in object naming. The language center was highly localized in many patients to form several mosaics of 1 to 2 sq cm, usually one in the frontal and one or more in the temporoparietal lobe. The area of individual mosaics, and the total area related to language was usually much smaller than the traditional Broca-Wernicke areas. There was substantial individual variability in the exact location of language function, some of which correlated with the patient's sex and verbal intelligence. These features were present for patients as young as 4 years and as old as 80 years, and for those with lesions acquired in early life or adulthood. These findings indicate a need for revision of the classical model of language localization. The combination of discrete localization in individual patients but substantial individual variability between patients also has major clinical implications for cortical resections of the dominant hemisphere, for it means that language cannot be reliably localized on anatomic criteria alone. A maximal resection with minimal risk of postoperative aphasia requires individual localization of language with a technique like stimulation mapping.

Article Information

Address reprint requests to: George Ojemann, M.D., Department of Neurological Surgery, University of Washington, RI-20, Seattle, Washington 98195.

© AANS, except where prohibited by US copyright law.

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    Sites essential for naming (filled circles) in a 24-year-old woman with a verbal IQ of 81. Stimulation at 6 mA; control error rate in the absence of stimulation was 3.7%. Open circles indicate stimulation sites without evoked errors; single nonsignificant error shown by a small dot. M and S identify sites with motor (M) or sensory (S) responses. Note the localized posterior language area with closely spaced surrounding stimulation sites without errors.

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    Sites essential for naming (filled circles) in a 46-year-old woman with a verbal IQ of 91. Stimulation at 7 mA; control error rate in the absence of stimulation was 6%. Open circles indicate stimulation sites without evoked errors. Note the relatively large posterior language area, but very localized anterior language site, and a language site in the anterior superior temporal gyrus (arrow) in front of rolandic cortex, 4 cm from the temporal tip. M and S indicate sites with motor (M) or sensory (S) responses.

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    Sites of significant evoked naming errors (filled circles) in a 4-year-old boy (upper) and a 70-year-old man (lower), both with medial temporal lobe gliomas. Open circles indicate stimulation sites without evoked errors. The 4-year-old boy was stimulated through a chronic subdural grid. Note that both patients show very localized temporal language sites. M and S indicate sites with motor (M) or sensory (S) responses.

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    Large dominant hemisphere temporoparietal resections of much of the classical Wernicke area in two patients, with no postoperative worsening of language function. The resections spared the sites of repeated evoked naming errors. Both patients had only left-sided speech areas based on preoperative intracarotid amobarbital perfusion testing. Filled circles indicate sites essential for naming; open circles indicate stimulation sites without evoked errors; single nonsignificant error shown by a small dot. M and S indicate sites with motor (M) or sensory (S) responses. Upper: This patient with superior temporal gyms oligodendroglioma and intractable seizures experienced no language change after the resection delineated by the shaded area. The patient returned to teaching postoperatively. Lower: This patient with widespread lateral temporal epileptic focus had no language deficits preoperatively. Following the resection indicated by the shaded area, oral language returned to normal within a week, although reading remained slow for a longer period.

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    Variability in language localization in 117 patients. Individual maps are aligned as described in the text, and cortex is divided into zones identified by dashed lines. Upper number in each zone is the number of patients with a site in that zone; lower number in circle is the percentage of those patients with sites of significant evoked naming errors in that zone. M and S indicate motor (M) or sensory (S) cortex.

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    Sites essential for naming (filled circles) in a 24-year-old woman with a verbal IQ of 94. Stimulation at 2 mA; control error rate in the absence of stimulation was 1.2%. Open circles indicate stimulation sites without evoked errors; single nonsignificant error shown by a small dot. The posterior language area (slightly larger than in the patient illustrated in Fig. 1) is oriented transversely to the superior temporal gyrus. Note also that the intensity of the stimulating current does not determine the size of language area (compare to Fig. 1). M indicates sites with motor response.

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    Sites essential for naming (filled circles) in an 18-year-old woman with a verbal IQ of 95. Stimulation at 4 mA; control error rate in the absence of stimulation was 0%. Open circles indicate stimulation sites without evoked errors. This patient was left-handed, but had only left language according to the intracarotid amobarbital perfusion test. Language in this unusual parietal location imposes no limits on a temporal resection. M and S indicate sites with motor (M) or sensory

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    Sites essential for naming (filled circles) in a 37-year-old woman with a verbal IQ of 99. Stimulation at 6 mA; control error rate in the absence of stimulation was 0%. Open circles indicate stimulation sites without evoked errors; single nonsignificant error shown by small dots. No posterior language sites were identified despite extensive mapping. A posterior temporal resection (dashed line) was associated with no language changes, even acutely. M and S indicate sites with motor (M) or sensory (S) responses.

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    Sites essential for naming (filled circles) in an 18-year-old man with a verbal IQ of 91. Stimulation at 5 mA; control error rate in the absence of stimulation was 1.7%. Open circles indicate stimulation sites without evoked errors; single nonsignificant error shown by a small dot. No changes in naming or counting were evoked at frontal sites. M and S indicate sites with motor (M) or sensory (S) responses.

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    Sites essential for naming (filled circles) in a 20-year-old man with a verbal IQ of 91. Stimulation at 5 mA; control error rate in the absence of stimulation was 0%. Open circles indicate stimulation sites without evoked errors; single nonsignificant error shown by small dots. Inferior frontal language sites extend nearly to the pterion. The frontal resection came within 1 cm of the anterior language area, and was followed by a significant expression aphasia lasting several weeks. M and S indicate sites with motor (M) or sensory (S) responses.

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    Site of evoked naming errors (filled circles) in a 45-year-old man following removal of a parietal glioma (shaded area) that exposed the planum temporale. Note the localized site of evoked naming errors on the planum (arrow), adjacent to a similar superior temporal gyrus surface site. Stimulation at 4 mA; control error rate in the absence of stimulation was 0.9%. Open circles indicate stimulation sites without evoked errors. No naming errors were evoked from stimulation of cortex overlying the tumor and no language disturbance followed the resection. M and S indicate sites with motor (M) or sensory (S) responses.

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    Sex and VIQ differences in language localization*

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