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Geert-Jan Rutten and Nick Ramsey

Dissociated language functions are largely invalidated by standard techniques such as the amobarbital test and cortical stimulation. Language studies in which magnetoencephalography (MEG) and functional magnetic resonance (fMR) imaging are used to record data while the patient performs lexicosemantic tasks have enabled researchers to perform independent brain mapping for temporal and frontal language functions (MEG is used for temporal and fMR imaging for frontal functions). In this case report, the authors describe a right-handed patient in whom a right-sided insular glioma was diagnosed. The patient had a right-lateralized receptive language area, but expressive language function was identified in the left hemisphere on fMR imaging– and MEG-based mapping. Examinations were performed in 20 right-handed patients with low-grade gliomas (control group) for careful comparison with and interpretation of this patient's results. In these tests, all patients were asked to generate verbs related to acoustically presented nouns (verb generation) for fMR imaging, and to categorize as abstract or concrete a set of visually presented words consisting of three Japanese letters for fMR imaging and MEG.

The most prominent display of fMR imaging activation by the verb-generation task was observed in the left inferior and middle frontal gyri in all participants, including the patient presented here. Estimated dipoles identified with the abstract/concrete categorization task were concentrated in the superior temporal and supra-marginal gyri in the left hemisphere in all control patients. In this patient, however, the right superior temporal region demonstrated significantly stronger activations on MEG and fMR imaging with the abstract/concrete categorization task. Suspected dissociation of the language functions was successfully mapped with these two imaging modalities and was validated by the modified amobarbital test and the postoperative neurological status. The authors describe detailed functional profiles obtained in this patient and review the cases of four previously described patients in whom dissociated language functions were found.

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Geert-Jan Rutten and Nick F. Ramsey

New functional neuroimaging techniques are changing our understanding of the human brain, and there is now convincing evidence to move away from the classic and clinical static concepts of functional topography. In a modern neurocognitive view, functions are thought to be represented in dynamic large-scale networks. The authors review the current (limited) role of functional MR imaging in brain surgery and the possibilities of new functional MR imaging techniques for research and neurosurgical practice. A critique of current clinical gold standard techniques (electrocortical stimulation and the Wada test) is given.

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Kuan H. Kho, Frans S. S. Leijten, Geert-Jan Rutten, Jan Vermeulen, Peter van Rijen and Nick F. Ramsey

✓ The Wada test is still considered the gold standard for determining the language-dominant hemisphere prior to brain surgery. The authors report on a 34-year-old right-handed woman whose Wada test results indicated that the right hemisphere was dominant for language. In contrast, functional magnetic resonance (fMR) imaging was indicative of bilaterally represented language functions. Activation in the left hemisphere demonstrated on fMR imaging was most pronounced in the Broca area. Importantly, fMR imaging results in this area were confirmed on electrocortical stimulation mapping. These contradictory findings indicated that a right hemispherre dominance for language according to the Wada test should be questioned and verified using electrocortical stimulation. Nonetheless, the question remains whether involvement of these areas in the left frontal hemisphere is critical for language, as these were spared during surgery.

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Kuan H. Kho, Geert-Jan M. Rutten, Frans S. S. Leijten, Arjen van der Schaaf, Peter C. van Rijen and Nick F. Ramsey

✓Electrocortical stimulation mapping (ESM) is the clinical standard for localizing critical sensorimotor and language functions, but other functions can be assessed with this technique as well. The authors describe an 8-year-old girl with a left frontal desmoplastic gangliocytoma and medically intractable epilepsy who underwent a chronic invasive recording using electrode grids. Prior to electrode implantation, functional magnetic resonance (fMR) imaging was performed using a research protocol that included a working memory task. The ESM procedure interfered with working memory at a dorsolateral prefrontal site as predicted by fMR imaging, but because this site was part of the epileptogenic region, it was included in the resection. Since the operation the patient has been seizure free and her overall cognitive performance has improved. Yet she shows a selective impairment in working memory tasks that has persisted for over two years, indicating that the area identified using fMR imaging and ESM was critically involved in working memory. Her performance did improve, however, suggesting that compensatory mechanisms took place. This case reveals an important and perhaps critical function of the dorsolateral prefrontal cortex. Work continues to assess the specific cognitive functions subserved by the region identified with fMR imaging and ESM.

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Geert-Jan Rutten, Nick Ramsey, Herke-Jan Noordmans, Peter Willems, Peter van Rijen, Jan Willem Berkelbach van der Sprenkel, Max Viergever and Cees van Veelen

In recent years, surgical navigation systems have become equipped to allow incorporation of data such as functional neuronavigation data. Functional magnetic resonance (fMR) imaging is a noninvasive modality that demonstrates various brain functions. Although still in an experimental stage, fMR imaging is a promising tool for mapping of motor and language functions. One advantage is that it can be implemented in presurgical imaging protocols and is therefore potentially widely available in general neurosurgical practice. In this paper the integration of fMR imaging and surgical navigation is described, and the potential advantages and pitfalls of its application in clinical practice are discussed.