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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.

Intraoperative brain mapping techniques were used to localize language cortex, sensorimotor pathways, and seizure foci in children with supratentorial brain tumors. The methods of direct cortical and subcortical stimulation, in addition to electrocorticography, enabled us to maximize tumor resection, minimize morbidity, and eradicate epileptogenic zones which were always adjacent to, but not involving, the tumor nidus. Language localization was found to be quite variable in the children tested and anatomically unpredictable based on the preoperative neurological or radiological examination. Physiological mapping techniques, therefore, appear to be safe, reliable, and very useful for operations on tumors located within or adjacent to eloquent brain regions in the pediatric population.

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We have recorded neuronal responses in the lateral temporal lobe of man to overt speech during open brain surgery for epilepsy. Tests included overt naming of objects and reading words or short sentences shown on a projector screen, repetition of tape recorded words or sentences presented over a loudspeaker, and free conversation. Neuronal activity in the dominant and non-dominant temporal lobe were about equally affected by overt speech. As during listening to language (see Creutzfeldt et al. 1989), responses differed between recordings from sites in the superior and the middle or inferior temporal gyrus. In the superior temporal gyrus all neurons responded clearly and each in a characteristic manner. Activation could be related to phonemic aspects, to segmentation or to the length of spoken words or sentences. However, neurons were mostly differently affected by listening to words and language as compared to overt speaking. In neuronal populations recorded simultaneously with one or two microelectrodes, some neurons responded predominantly to one or the other type of speech. Excitatory responses during overt speaking were always auditory. In the middle temporal gyrus more neurons (about 2/3) responded to overt speaking than to listening alone. Activations elicited during overt speech were seen in about 1/3 of our sample, but they were more sluggish than those recorded in the superior gyrus. A prominent feature was suppression of on-going activity, which we found in about 1/3 of middle and in some superior temporal gyrus neurons. This suppression could precede vocalization by up to a few hundred ms, and could outlast it by up to 1 s. Evoked ECoG-potentials to words heard or spoken were different, and those to overt speech were more widespread.

Some neurosurgeons state that intra-axial tumors may be resected with a low risk of neurological deficit if the tumor removal stays within the confines of the grossly abnormal tissue. This is thought to be so even when the lesion is presumably located in a functional area, providing that the adjacent normal-appearing cortex and subcortical white matter are not disturbed. This retrospective analysis presents evidence that this view is not always correct, because functioning motor, sensory, or language tissue can be located within a grossly obvious tumor or the surrounding infiltrated brain. Intraoperative stimulation mapping techniques identified 28 patients, ranging in age between 22 and 73 years, who showed evidence of functional tissue within the boundaries of infiltrative gliomas, as identified by correlation with computed tomography and magnetic resonance imaging scans, intraoperative ultrasound, gross visualization, and histological confirmation. Direct stimulation mapping of cortical and subcortical portions of the tumor during resections identified motor, sensory, naming, reading, or speech arrest function. Nineteen patients had new or worsened neurological deficits immediately after the operation, but after 3 months, only 6 continued to show new deficits whereas 18 showed no deficits and 2 improved. These results demonstrate that regardless of the degree of tumor infiltration, swelling, apparent necrosis, and gross distortion by the mass, functional cortex and subcortical white matter may be located within the tumor or the adjacent infiltrated brain. Therefore, to safely maximize glioma resection in these functional areas, intraoperative stimulation mapping may be used to identify functional cortical or subcortical tissue within, as well as adjacent to, the tumor, thus avoiding permanent injury.

Surgical removal of epileptogenic brain is indicated for treatment of many medically refractory focal seizure disorders. One of the important factors in providing good results from surgery is the accuracy of identifying the epileptogenic focus. However, accurate localization may be difficult when only standard scalp recordings are used. Many epilepsy centers have used intracranial recording techniques to better define regions of cortical epileptogenicity . Although subdural strip electrodes were first utilized many years ago, the more popular method of intracranial recording has been by intracortical depth electrodes. The authors present their method of placing subdural strip electrodes for extensive recordings from the cortex. To date, this method has been used to provide continuous monitoring of the electrocorticogram in 28 patients for periods up to 3 weeks, with only two minor complications. This procedure is relatively safe and a valuable alternative to placing intracortical depth electrodes.

The supplementary motor area (SMA) is a region located within each cerebral hemisphere at the posterior mesial border of the frontal lobe adjacent to the falx. The functional significance of this area has been somewhat unclear, and information regarding its influence on motor output has largely been based on evoked responses to direct stimulation in primates and humans. In this series of patients with primary and metastatic tumors involving the dominant hemisphere SMA, a distinct pattern of postoperative deficits and recovery has emerged which emphasizes the role of this critical area in the initiation of motor activity, including speech. Based upon this analysis, ablation of this region after first identifying the primary motor cortex may be accomplished without risk of permanent loss of motor activity or speech function, despite the initial severe deficits.