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George A. Ojemann

✓ Individual variability in the localization of language, as measured by object-naming, was assessed for left lateral peri-Sylvian cortex with a multi-sample technique of stimulation mapping at a constant current. This study was performed during craniotomy under local anesthesia in 10 patients with medically intractable epilepsy and the usual pattern of left brain dominance for language. A high degree of variability in the exact location of naming was present. Only one area, a small portion of the third frontal convolution immediately in front of the motor strip, showed naming changes in all patients in whom it was sampled. This area is considerably smaller than the classical Broca's area. Elsewhere in language cortex, including all parts of the posterior language area, there was considerable individual variability. Because of this, the classical model of language localization is an inaccurate basis for establishing the risk of aphasia in surgical therapy of dominant hemisphere peri-Sylvian lesions in this and related patient populations. Rather, that risk should be assessed from the individual localization of language, established by the multisample technique of stimulation mapping.

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George A. Ojemann

✓ There has been a recent renewal of interest in surgical therapy for medically intractable epilepsies. Cortical resection and callosotomy are the most widely accepted modes of surgical management. The indications for each of these approaches are reviewed. Although there has been much interest in imaging techniques, including positron emission tomography, to identify epileptogenic zones, identification still depends primarily on the electroencephalogram (EEG). There are several approaches to the evaluation and intraoperative management of patients undergoing cortical resection for temporal lobe epileptogenic zones. These range from selection based on scalp interictal EEG criteria, with resections guided by electrocorticography and functional mapping, to selection based on the location of ictal onset as recorded by chronically implanted depth electrodes, with an anatomically standard resection of the temporal lobe or resection limited to amygdalohippocampectomy. No one approach provides the optimum balance of benefits to risks and costs for all patients.

The relative value of the different approaches for various populations of patients with medically intractable partial complex seizures is reviewed. Techniques for minimizing the morbidity of these operations, especially in regard to language and memory, are also discussed, as are the contributions to an understanding of the neurobiology of human epilepsy and human higher functions derived from the surgical therapy of epilepsy.

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George A. Ojemann and Carl B. Dodrill

✓ Verbal memory deficits remain a major complication of dominant hemisphere temporal lobectomy for epilepsy. The extent of this deficit was assessed preoperatively and 1 month and 1 year postoperatively with the Wechsler Verbal Memory Scale (WMSV) in 14 adults undergoing left temporal lobectomy. Intraoperative localization of language and verbal memory was also performed by electrical stimulation mapping. The WMSV score decreased an average of 22% at 1 month (13 cases), and 11% at 1 year (10 cases), even though in the majority of cases the medial extent of the resections had been significantly modified as a result of preoperative memory changes in response to intracarotid amobarbital perfusion testing. Memory decline was greater in patients who were not seizure-free, and correlated with the lateral (but not the medial) extent of the resection. The memory deficit could be predicted intraoperatively with 80% accuracy from the relationship of the resection to sites identified by electrical stimulation mapping as essential to naming or input or storage aspects of memory. This technique was applied prospectively in two additional cases with left temporal epileptic foci and complete verbal memory loss with left hemisphere amobarbital inactivation. These resections were tailored to avoid the essential naming and memory sites; the WMSV score increased 1 month postoperatively in both cases. This study identifies a lateral cortical component for verbal memory. Sites essential for that component can be localized intraoperatively with stimulation mapping; when they are spared in a resection, verbal memory deficit following dominant hemisphere temporal lobectomy can be prevented even in high-risk cases.

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Cortical language localization in left, dominant hemisphere

An electrical stimulation mapping investigation in 117 patients

George Ojemann, Jeff Ojemann, E. Lettich and M. Berger

✓ 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.

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Cortical language localization in left, dominant hemisphere

An electrical stimulation mapping investigation in 117 patients

George Ojemann, Jeff Ojemann, E. Lettich and M. Berger

✓ 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.

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Jeffrey G. Ojemann, George A. Ojemann and Ettore Lettich

Object. Cortical stimulation mapping has traditionally relied on disruption of object naming to define essential language areas. In this study, the authors reviewed the use of a different language task, verb generation, in mapping language. This task has greater use in brain imaging studies and may be used to test aspects of language different from those of object naming.

Methods. In 14 patients, cortical stimulation mapping performed using a verb generation task provided a map of language areas in the frontal and temporoparietal cortices. These verb generation maps often overlapped object naming ones and, in many patients, different areas of cortex were found to be involved in the two functions. In three patients, stimulation mapping was performed during the initial performance of the verb generation task and also during learned performance of the task. Parallel to findings of published neuroimaging studies, a larger area of stimulated cortex led to disruption of verb generation in response to stimulation during novel task performance than during learned performance.

Conclusions. Results of cortical stimulation mapping closely resemble those of functional neuroimaging when both implement the verb generation task. The precise map of the temporoparietal language cortex depends on the task used for mapping.

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Mitchel S. Berger, Wendy A. Cohen and George A. Ojemann

✓ Brain maps derived intraoperatively from patients undergoing tumor resection were correlated retrospectively with magnetic resonance (MR) images with respect to the precise localization of the motor cortex in an attempt to identify useful preoperative MR imaging landmarks that correspond to functional brain regions. Superior axial T2-weighted MR images consistently localized the central sulcus, whereas parasagittal and far-lateral sagittal images readily identified the rolandic (sensorimotor) cortex, as a functional unit, based on the cingulate-marginal sulcus and insula, respectively. It is therefore concluded that multiplanar MR images may serve as a useful preoperative planning aid prior to removing intrinsic brain tumors within or adjacent to the motor cortex.

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George A. Ojemann, Katharine Blick Hoyenga and Arthur A. Ward Jr.

✓ The acute change in short-term verbal memory following ventrolateral thalamotomy in patients with dyskinesia was measured by the technique of Peterson and Peterson. Performance on this test of short-term verbal memory deteriorated following left but not right ventrolateral thalamotomy. This deterioration could not be accounted for solely by disturbance in speech mechanisms after left thalamotomy (although these were present), but may be related to disturbance in retrieval mechanisms of short-term verbal memory. The relative magnitude of this deterioration in performance after left thalamotomy could be partially predicted at the time of operation by some of the effects of electrical stimulation of the ventrolateral thalamus on the same test. A large decrease in recall errors with stimulation during the presentation of material to be later recalled, and a small increase in recall errors with stimulation at the time of recall, correlated with little disturbance of short-term verbal memory following left thalamotomy.

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Richard W. Leech, F. Tod Welch and George A. Ojemann

✓ A case is reported in which bilateral subdural hematomas were caused by metastatic adenocarcinoma in the subdural membranes. This diffuse dural carcinomatosis was associated with widespread intravascular tumor growth and a marked vascular and fibrous proliferation, interpreted as a tumor-induced angiodesmoplasia. The hematomas resulted from separation and hemorrhage into this highly vascular abnormal areolar layer of the dura.

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Kim J. Burchiel, George A. Ojemann and Nicole Bolender

✓ A method is described for determining stereotaxic coordinates using computerized tomographic scanning and intraoperative ventriculography of the third ventricle.