Despite a better understanding of the organization of the cortical network underlying the semantic system, very few data are currently available regarding its anatomo-functional connectivity. Here, we report on a series of 17 patients operated on under local anaesthesia for a cerebral low-grade glioma located within the dominant hemisphere. Prior to and during resection, intraoperative electrical stimulation was used to map sensorimotor and language structures so that permanent neurological deficits could be avoided. In a number of cases, cortical and subcortical stimulation caused semantic paraphasias. Using postoperative MRI, we correlated these functional findings with the anatomical locations of the sites where semantic errors were elicited by stimulation, especially at the subcortical level, with the aim of studying the connectivity underlying the semantic system. In temporal gliomas, cortical sites involved in semantic processing were found around the posterior part of the superior temporal sulcus, with subcortical pathways reproducibly located under the depth of this sulcus. In insular gliomas, although stimulation elicited no semantic disturbances at the cortical level, such semantic paraphasias were generated at the level of the anterior floor of the external capsule. In frontal tumours, cortical regions implicated in semantics were detected in the lateral orbitofrontal region and dorsolateral prefrontal cortex, with subcortical fibres located under the inferior frontal sulcus. All these eloquent structures were systematically preserved, thereby avoiding permanent postoperative deficits. Our results provide arguments in favour of the existence of a main ventral subcortical pathway underlying the semantic system, within the dominant hemisphere, joining the two essential cortical epicentres of this network: the posterior and superior temporal areas, and the orbitofrontal and dorsolateral prefontal regions. Such a ventral stream might anatomically partly correspond to the inferior fronto-occipital fasciculus.

Although advances in diffusion tensor imaging have enabled us to better study the anatomy of the inferior longitudinal fasciculus (ILF), its function remains poorly understood. Recently, it was suggested that the subcortical network subserving the language semantics could be constituted, in parallel with the inferior occipitofrontal fasciculus, by the left ILF, joining the posterior occipitotemporal regions to the temporal pole, then relayed by the uncinate fasciculus connecting the anterior temporal pole to the frontobasal areas. Nevertheless, this hypothesis was solely based on neurofunctional imaging, allowing a cortical mapping but with no anatomofunctional information regarding the white matter. Here, we report a series of 12 patients operated on under local anaesthesia for a cerebral low-grade glioma located within the left temporal lobe. Before and during resection, we used the method of intraoperative direct electrostimulation, enabling us to perform accurate and reliable anatomofunctional correlations both at cortical and subcortical levels. In order to map the ILF. Using postoperative MRI, we correlated these functional findings with the anatomical locations of the sites where language disturbances were elicited by stimulations, both at cortical and subcortical levels. Our goal was to study the potential existence of parallel and distributed language networks crossing the left dominant temporal lobe, subserved by distinct subcortical pathways--namely the inferior occipitofrontal fasciculus and the ILF. Intraoperative stimulation of the anterior and middle temporal cortex elicited anomia in four patients. At the subcortical level, semantic paraphasia were induced in seven patients during stimulation of the inferior occipitofrontal fasciculus, and phonological paraphasia was generated in seven patients by stimulating the arcuate fasciculus. Interestingly, subcortical stimulation never elicited any language disturbances when performed at the level of the ILF. In addition, following a transient postoperative language deficit, all patients recovered, despite the resection of at least one part of the ILF, as confirmed by control MRI. On the basis of these results, we suggest that the "semantic ventral stream" could be constituted by at least two parallel pathways within the left dominant temporal lobe: (i) a direct pathway, the inferior occipitofrontal fasciculus, that connects the posterior temporal areas and the orbitofrontal region, crucial for language semantic processing, since it elicits semantic paraphasia when stimulated; (ii) and also possibly an indirect pathway subserved by the ILF, not indispensable for language, since it can be compensated both during stimulation and after resection.

The use of functional mapping of the white matter together with cortical mapping allowed the authors to optimize the benefit/risk ratio of surgery of low-grade glioma invading eloquent regions. Given that preoperative fiber tracking with the aid of neuroimaging is not yet validated, we used intraoperative real-time cortical and subcortical stimulations as a valuable adjunct to the other mapping methods.

Despite a better understanding of the anatomy of the uncinate fasciculus (UF), its function remains poorly known. Our aim was to study the exact role of UF in language, and the possible existence of parallel distributed language networks within the "ventral stream", underlaid by distinct subcortical tracts--namely the inferior occipito-temporal fasciculus (IOF) and UF.We report a series of 13 patients operated on awake for a glioma involving the left anterior temporal lobe or the orbitofrontal area. We used intraoperative electrostimulation, to perform accurate and reliable anatomofunctional correlations both at cortical and subcortical levels. Using postoperative MRI, we correlated these functional findings with the anatomical locations of the sites where language disturbances were elicited by stimulation.Intraoperative cortical stimulation found perilesional language sites in all cases. Subcortically, semantic paraphasia were induced in the 13 patients by stimulating the IOF, and phonological paraphasia were generated in 6 patients by stimulating the arcuate fasciculus. Interestingly, subcortical stimulation never elicited any language disturbances when performed at the level of the UF. Moreover, after a transient postoperative language deficit, all patients recovered, despite the removal of at least one part of the UF, as confirmed by control MRI.We suggest that UF is not systematically essential for language. It can be explained by the fact that the "semantic ventral stream" might be constituted by at least two parallel pathways, i. e. a direct pathway underlaid by the IOF, crucial for language semantics, and an indirect pathway subserved by UF, which can be functionally compensated. However, we have to underline the fact not all language functions can be probed during surgery, and that more sensitive tasks have now to be added.