•Data issued from brain stimulation enables to re-examine the neural basis of language.•A hodotopical model of language processing challenges the modular view.•This model is based on parallel ...distributed cortico-subcortical subnetworks.•Phonological, semantic and syntactic processing are served by distinct sub-circuits.•Anatomic constraints are incorporated into this dynamic model.
From recent findings provided by brain stimulation mapping during picture naming, we re-examine the neural basis of language. We studied structural–functional relationships by correlating the types of language disturbances generated by stimulation in awake patients, mimicking a transient virtual lesion both at cortical and subcortical levels (white matter and deep grey nuclei), with the anatomical location of the stimulation probe. We propose a hodotopical (delocalized) and dynamic model of language processing, which challenges the traditional modular and serial view. According to this model, following the visual input, the language network is organized in parallel, segregated (even if interconnected) large-scale cortico-subcortical sub-networks underlying semantic, phonological and syntactic processing. Our model offers several advantages (i) it explains double dissociations during stimulation (comprehension versus naming disorders, semantic versus phonemic paraphasias, syntactic versus naming disturbances, plurimodal judgment versus naming disorders); (ii) it takes into account the cortical and subcortical anatomic constraints; (iii) it explains the possible recovery of aphasia following a lesion within the “classical” language areas; (iv) it establishes links with a model executive functions.
The heterogeneity and complexity of white matter (WM) pathways of the human brain were discretely described by pioneers such as Willis, Stenon, Malpighi, Vieussens and Vicq d'Azyr up to the beginning ...of the 19th century. Subsequently, novel approaches to the gross dissection of brain internal structures have led to a new understanding of WM organization, notably due to the works of Reil, Gall and Burdach highlighting the fascicular organization of WM. Meynert then proposed a definitive tripartite organization in association, commissural and projection WM pathways. The enduring anatomical work of Dejerine at the turn of the 20th century describing WM pathways in detail has been the paramount authority on this topic (including its terminology) for over a century, enriched sporadically by studies based on blunt Klingler dissection. Currently, diffusion-weighted magnetic resonance imaging (DWI) is used to reveal the WM fiber tracts of the human brain
by measuring the diffusion of water molecules, especially along axons. It is then possible by tractography to reconstitute the WM pathways of the human brain step by step at an unprecedented level of precision in large cohorts. However, tractography algorithms, although powerful, still face the complexity of the organization of WM pathways, and there is a crucial need to benefit from the exact definitions of the trajectories and endings of all WM fascicles. Beyond such definitions, the emergence of DWI-based tractography has mostly revealed strong heterogeneity in naming the different bundles, especially the long-range association pathways. This review addresses the various terminologies known for the WM association bundles, aiming to describe the rules of arrangements followed by these bundles and to propose a new nomenclature based on the structural wiring diagram of the human brain.
Despite recent advances in non-invasive brain mapping imaging, the resectability of a given area in a patient harboring a WHO grade II glioma cannot be predicted preoperatively with high reliability, ...due to mechanisms of functional reorganization. Therefore, intraoperative mapping by direct electrical stimulation remains the gold standard for detection and preservation of eloquent areas during glioma surgery, because it enables to perform on-line anatomo-functional correlations. To study potentials and limitations of brain plasticity, we gathered 58 postoperative MRI of patients operated on for a WHO grade II glioma under direct electrical cortico-subcortical stimulation. Postoperative images were registered on the MNI template to construct an atlas of functional resectability for which each voxel represents the probability to observe residual non-resectable tumor, that is, non-compensable area. The resulting atlas offers a rigorous framework to identify areas with high plastic potential (i.e. with probabilities of residual tumor close to 0), with low compensatory capabilities (i.e. probabilities of residual tumor close to 1) and with intermediate level of resectability (probability around 0.5). The resulting atlas highlights the utmost importance of preserving a core of connectivity through the main associative pathways, namely, it supports the existence of a “minimal common brain” among patients.
►Resectability of brain areas is unpredictable before tumor surgery due to reshaping. ►Electrical mapping allows the study of potentials and limitations of plasticity. ►We build an atlas of functional resectability based on postoperative residue. ►Each voxel represents the probability to observe non-compensable area. ►Our atlas highlights the existence of a “minimal common brain” among patients.
Over the past two decades, it has been demonstrated that brain mapping in an awake patient is a very reliable tool for brain tumor resection, allowing us to maximize the extent of resection while ...minimizing the functional risk.1 This methodology is becoming more and more popular, and different teams have introduced many new tasks in their intraoperative battery, for motor functions2 as well as for cognitive functions.3,4 While the aim of preserving functions better and better cannot be blamed, it should be kept in mind that selecting for each case a personalized minimal set of tasks is crucial: the awake surgery team has to find an optimal trade-off between the number of tasks incorporated in the intraoperative battery and the limited amount of time of the awake period (about 2 h, in keeping with the onset of the patient's tiredness, which renders monitoring unreliable). More than that, there is a risk of introducing tasks that would be too sensitive, in the sense that the removal of a positive site would not necessarily lead to a permanent deficit of the function, meaning that brain mapping would restrict the extent of resection for no good reasons. We, thus, would like to highlight in this letter that the introduction of a new task tapping a specific sensorimotor, cognitive, or emotional process should follow a strict scientific plan.
Awake surgery for low-grade gliomas is currently considered the best procedure to improve the extent of resection and guarantee a "worth living life" for patients, meaning avoiding not only motor but ...also cognitive deficits. However, tumors located in the right hemisphere, especially in the right frontal lobe, are still rarely operated on in awake condition; one of the reasons possibly being that there is little information in the literature describing the rates and nature of long-lasting neuropsychological deficits following resection of right frontal glioma. To investigate long-term cognitive deficits after awake surgery in right frontal IDH-mutated glioma. We retrospectively analyzed a consecutive series of awake surgical resections between 2012 and 2020 for right frontal IDH-mutated glioma. We studied the patients' subjective complaints and objective neuropsychological evaluations, both before and after surgery. Our results were then put in perspective with the literature. Twenty surgical cases (including 5 cases of redo surgery) in eighteen patients (medium age: 42.5 range 26-58) were included in the study. The median preoperative volume was 37 cc; WHO grading was II, III and IV in 70%, 20%, and 10% of cases, respectively. Preoperatively, few patients had related subjective cognitive or behavioral impairment, while evaluations revealed mild deficits in 45% of cases, most often concerning executive functions, attention, working memory and speed processing. Immediate postoperative evaluations showed severe deficits of executive functions in 75% of cases but also attentional deficits (65%), spatial neglect (60%) and behavioral disturbances (apathy, aprosodia/amimia, emotional sensitivity, anosognosia). Four months after surgery, although psychometric z-scores were unchanged at the group level, individual evaluations showed a slight decrease of performance in 9/20 cases for at least one of the following domains: executive functions, speed processing, attention, semantic cognition, social cognition. Our results are generally consistent with those of the literature, confirming that the right frontal lobe is a highly eloquent area and suggesting the importance of operating these patients in awake conditions.
In this paper, we review the literature about the definitions of errors observed by direct electrical stimulation during language testing. As a practical application, we propose an optimized strategy ...for differentiating accurately motor arrest, speech arrest, and anomia in the context of intraoperative mapping. Finally, we also discuss the anatomical correlates of the networks sustaining these different errors, both cortically and axonally.
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