Limited plastic potential of the left ventral premotor cortex in speech articulation: evidence from intraoperative awake mapping in glioma patients

Postoperative reorganization of the supplementary motor area complex: A possible latent bihemispheric network

PURPOSE

Brain plasticity after multistep surgery in low-grade glioma is highly variable; the neurosurgical approach must be individualised and functional imaging can be used for this purpose. In supplementary motor area complex (SMAC) tumors, the early and adequate functional recovery of patients raises the possibility of a latent bihemispheric or "mirror" cortico-subcortical network, which would develop depending on the needs of each patient.

METHODS

Functional and DTI-MR data from 4 right-handed patients with left frontal low grade gliomas near the SMAC, who were operated at least in two occasions were collected. The time of the reintervention was variable (18 months- 8 years), related to the tumor growth. All patients were evaluated by a neuropsychologist and imaged before each surgery, in a 3 T MR, with a 24 multichanel head coil Motor and expressive language task-fMRI and DTI sequences were obtained to evidence the main cortico-subcortical components of the SMAC. Data were processed with Brainwave (GE Medical Systems) and with an Iplan Fiber Tracking tool (MEDTRONIC), respectively RESULTS: None of our patients presented permanent neurological deficits after the first or second functional surgery. Three patients with partial or complete resection of the left middle and / or inferior frontal gyrus, and the left frontal aslant tract evidenced new right hemispherical cortical activity. This right shift were not observed in the patient without left middle gyrus resection, indeed with partial absent of the left frontal aslant tract.

CONCLUSION

SMAC is a latent cortico-subcortical bihemispheric network that allows it to reorganize itself in response to specific neurological deficits. We highlight the importance in the cortical reorganization of the left middle frontal gyrus in the SMAC, closely connected with the essential language areas of this region, but also we focused in the potential cortioco-subcortical changes to compensate the functionality of the FAT.

Fibration symmetry-breaking supports functional transitions in a brain network engaged in language

In his book 'A Beautiful Question', physicist Frank Wilczek argues that symmetry is 'nature's deep design,' governing the behavior of the universe, from the smallest particles to the largest structures. While symmetry is a cornerstone of physics, it has not yet been found widespread applicability to describe biological systems, particularly the human brain. In this context, we study the human brain network engaged in language and explore the relationship between the structural connectivity (connectome or structural network) and the emergent synchronization of the mesoscopic regions of interest (functional network). We explain this relationship through a different kind of symmetry than physical symmetry, derived from the categorical notion of Grothendieck fibrations. This introduces a new understanding of the human brain by proposing a local symmetry theory of the connectome, which accounts for how the structure of the brain's network determines its coherent activity. Among the allowed patterns of structural connectivity, synchronization elicits different symmetry subsets according to the functional engagement of the brain. We show that the resting state is a particular realization of the cerebral synchronization pattern characterized by a fibration symmetry that is broken in the transition from rest to language. Our findings suggest that the brain's network symmetry at the local level determines its coherent function, and we can understand this relationship from theoretical principles.

Fibration symmetry-breaking supports functional transitions in a brain network engaged in language

In his book 'A Beautiful Question' 1, physicist Frank Wilczek argues that symmetry is 'nature's deep design,' governing the behavior of the universe, from the smallest particles to the largest structures 1-4. While symmetry is a cornerstone of physics, it has not yet been found widespread applicability to describe biological systems 5, particularly the human brain. In this context, we study the human brain network engaged in language and explore the relationship between the structural connectivity (connectome or structural network) and the emergent synchronization of the mesoscopic regions of interest (functional network). We explain this relationship through a different kind of symmetry than physical symmetry, derived from the categorical notion of Grothendieck fibrations 6. This introduces a new understanding of the human brain by proposing a local symmetry theory of the connectome, which accounts for how the structure of the brain's network determines its coherent activity. Among the allowed patterns of structural connectivity, synchronization elicits different symmetry subsets according to the functional engagement of the brain. We show that the resting state is a particular realization of the cerebral synchronization pattern characterized by a fibration symmetry that is broken 7 in the transition from rest to language. Our findings suggest that the brain's network symmetry at the local level determines its coherent function, and we can understand this relationship from theoretical principles.

Current State of Functional MRI in the Presurgical Planning of Brain Tumors

Surgical resection of brain tumors is challenging because of the delicate balance between maximizing tumor removal and preserving vital brain functions. Functional MRI (fMRI) offers noninvasive preoperative mapping of widely distributed brain areas and is increasingly used in presurgical functional mapping. However, its impact on survival and functional outcomes is still not well-supported by evidence. Task-based fMRI (tb-fMRI) maps blood oxygen level-dependent (BOLD) signal changes during specific tasks, while resting-state fMRI (rs-fMRI) examines spontaneous brain activity. rs-fMRI may be useful for patients who cannot perform tasks, but its reliability is affected by tumor-induced changes, challenges in data processing, and noise. Validation studies comparing fMRI with direct cortical stimulation (DCS) show variable concordance, particularly for cognitive functions such as language; however, concordance for tb-fMRI is generally greater than that for rs-fMRI. Preoperative fMRI, in combination with MRI tractography and intraoperative DCS, may result in improved survival and extent of resection and reduced functional deficits. fMRI has the potential to guide surgical planning and help identify targets for intraoperative mapping, but there is currently limited prospective evidence of its impact on patient outcomes. This review describes the current state of fMRI for preoperative assessment in patients undergoing brain tumor resection. Keywords: MR-Functional Imaging, CNS, Brain/Brain Stem, Anatomy, Oncology, Functional MRI, Functional Anatomy, Task-based, Resting State, Surgical Planning, Brain Tumor © RSNA, 2023.

The arcuate fasciculus: Combining structure and function into surgical considerations

BACKGROUND

Two Centuries from today, Karl Friedrich Burdach attributed the nomenclature "arcuate fasciculus" to a white matter (WM) pathway connecting the frontal to the temporal cortices by arching around the Sylvian fissure. Although this label remained essentially unvaried, the concepts related to it and the characterization of the structural properties of this bundle evolved along with the methodological progress of the past years. Concurrently, the functional relevance of the arcuate fasciculus (AF) classically restricted to the linguistic domain has extended to further cognitive abilities. These features make it a relevant structure to consider in a large variety of neurosurgical procedures.

OBJECTIVE

Herein, we build on our previous review uncovering the connectivity provided by the Superior Longitudinal System, including the AF, and provide a handy representation of the structural organization of the AF by considering the frequency of defined reports in the literature. By adopting the same approach, we implement an account of which functions are mediated by this WM bundle. We highlight how this information can be transferred to the neurosurgical field by presenting four surgical cases of glioma resection requiring the evaluation of the relationship between the AF and the nearby structures, and the safest approaches to adopt.

CONCLUSIONS

Our cumulative overview reports the most common wiring patterns and functional implications to be expected when approaching the study of the AF, while still considering seldom descriptions as an account of interindividual variability. Given its extension and the variety of cortical territories it reaches, the AF is a pivotal structure for different cognitive functions, and thorough understanding of its structural wiring and the functions it mediates is necessary for preserving the patient's cognitive abilities during glioma resection.

Intraoperative functional remapping unveils evolving patterns of cortical plasticity

The efficiency with which the brain reorganizes following injury not only depends on the extent and the severity of the lesion, but also on its temporal features. It is established that diffuse low-grade gliomas (DLGG), brain tumours with a slow-growth rate, induce a compensatory modulation of the anatomo-functional architecture, making this kind of tumours an ideal lesion model to study the dynamics of neuroplasticity. Direct electrostimulation (DES) mapping is a well-tried procedure used during awake resection surgeries to identify and spare cortical epicentres which are critical for a range of functions. Because DLGG is a chronic disease, it inevitably relapses years after the initial surgery, and thus requires a second surgery to reduce tumour volume again. In this context, contrasting the cortical mappings obtained during two sequential neurosurgeries offers a unique opportunity to both identify and characterize the dynamic (i.e. re-evolving) patterns of cortical re-arrangements. Here, we capitalized on an unprecedented series of 101 DLGG patients who benefited from two DES-guided neurosurgeries usually spaced several years apart, resulting in a large DES dataset of 2082 cortical sites. All sites (either non-functional or associated with language, speech, motor, somatosensory and semantic processing) were recorded in Montreal Neurological Institute (MNI) space. Next, we used a multi-step approach to generate probabilistic neuroplasticity maps that reflected the dynamic rearrangements of cortical mappings from one surgery to another, both at the population and individual level. Voxel-wise neuroplasticity maps revealed regions with a relatively high potential of evolving reorganizations at the population level, including the supplementary motor area (SMA, Pmax = 0.63), the dorsolateral prefrontal cortex (dlPFC, Pmax = 0.61), the anterior ventral premotor cortex (vPMC, Pmax = 0.43) and the middle superior temporal gyrus (STG Pmax = 0.36). Parcel-wise neuroplasticity maps confirmed this potential for the dlPFC (Fisher's exact test, PFDR-corrected = 6.6 × 10-5), the anterior (PFDR-corrected = 0.0039) and the ventral precentral gyrus (PFDR-corrected = 0.0058). A series of clustering analyses revealed a topological migration of clusters, especially within the left dlPFC and STG (language sites); the left vPMC (speech arrest/dysarthria sites) and the right SMA (negative motor response sites). At the individual level, these dynamic changes were confirmed for the dlPFC (bilateral), the left vPMC and the anterior left STG (threshold free cluster enhancement, 5000 permutations, family-wise error-corrected). Taken as a whole, our results provide a critical insight into the dynamic potential of DLGG-induced continuing rearrangements of the cerebral cortex, with considerable implications for re-operations.

Situation updating during discourse comprehension recruits right posterior portion of the multiple-demand network

Discourse comprehension involves the construction of a mental representation of the situation model as well as a continuous update of this representation. This mental update is cognitively demanding and likely engages the multiple-demand network. However, there is little evidence for the involvement of the multiple-demand network during situation updating. In this study, we used fMRI to test whether situation updating based on the change of spatial location activated the multiple-demand network. In a discourse comprehension task, readers read two-sentence discourses in which the second sentence either continues or introduces a shift of the spatial location information presented in the first sentence. Compared to situation continuation, situation updating reliably activated the right superior parietal lobule. This area is a part of the multiple-demand network as defined by a digit N-back localizer task and locates within the dorsal attention network as defined in the previous study by Yeo et al. in 2011. Our results provide evidence for the reliable involvement of a specific area of the multiple-demand network in situation updating during high-level discourse processing.

Preoperative individual-target transcranial magnetic stimulation demonstrates an effect comparable to intraoperative direct electrical stimulation in language-eloquent glioma mapping and improves postsurgical outcome: A retrospective fiber-tracking and electromagnetic simulation study

Background

Efforts to resection of glioma lesions located in brain-eloquent areas must balance the extent of resection (EOR) and functional preservation. Currently, intraoperative direct electrical stimulation (DES) is the gold standard for achieving the maximum EOR while preserving as much functionality as possible. However, intraoperative DES inevitably involves risks of infection and epilepsy. The aim of this study was to verify the reliability of individual-target transcranial magnetic stimulation (IT-TMS) in preoperative mapping relative to DES and evaluate its effectiveness based on postsurgical outcomes.

Methods

Sixteen language-eloquent glioma patients were enrolled. Nine of them underwent preoperative nTMS mapping (n=9, nTMS group), and the other seven were assigned to the non-nTMS group and did not undergo preoperative nTMS mapping (n=7). Before surgery, online IT-TMS was performed during a language task in the nTMS group. Sites in the cortex at which this task was disturbed in three consecutive trials were recorded and regarded as positive and designated nTMS hotspots (HS_nTMS). Both groups then underwent awake surgery and intraoperative DES mapping. DES hotspots (HS_DES) were also determined in a manner analogous to HS_nTMS. The spatial distribution of HS_nTMS and HS_DES in the nTMS group was recorded, registered in a single brain template, and compared. The center of gravity (CoG) of HS_nTMS (HS_nTMS-CoG)-based and HS_DES-CoG-based diffusion tensor imaging-fiber tracking (DTI-FT) was performed. The electromagnetic simulation was conducted, and the values were then compared between the nTMS and DES groups, as were the Western Aphasia Battery (WAB) scale and fiber-tracking values.

Results

HS_nTMS and HS_DES showed similar distributions (mean distance 6.32 ± 2.6 mm, distance range 2.2-9.3 mm, 95% CI 3.9-8.7 mm). A higher fractional anisotropy (FA) value in nTMS mapping (P=0.0373) and an analogous fiber tract length (P=0.2290) were observed. A similar distribution of the electric field within the brain tissues induced by nTMS and DES was noted. Compared with the non-nTMS group, the integration of nTMS led to a significant improvement in language performance (WAB scores averaging 78.4 in the nTMS group compared with 59.5 in the non-nTMS group, P=0.0321 < 0.05) as well as in brain-structure preservation (FA value, P=0.0156; tract length, P=0.0166).

Conclusion

Preoperative IT-TMS provides data equally crucial to DES and thus facilitates precise brain mapping and the preservation of linguistic function.

Predictive model of language deficit after removing glioma involving language areas under general anesthesia

Purpose

To establish a predictive model to predict the occurrence of language deficit for patients after surgery of glioma involving language areas (GILAs) under general anesthesia (GA).

Methods

Patients with GILAs were retrospectively collected in our center between January 2009 and December 2020. Clinical variables (age, sex, aphasia quotient [AQ], seizures and KPS), tumor-related variables (recurrent tumor or not, volume, language cortices invaded or not, shortest distance to language areas [SDLA], supplementary motor area or premotor area [SMA/PMA] involved or not and WHO grade) and intraoperative multimodal techniques (used or not) were analyzed by univariate and multivariate analysis to identify their association with temporary or permanent language deficits (TLD/PLD). The predictive model was established according to the identified significant variables. Receiver operating characteristic (ROC) curve was used to assess the accuracy of the predictive model.

Results

Among 530 patients with GILAs, 498 patients and 441 patients were eligible to assess TLD and PLD respectively. The multimodal group had the higher EOR and rate of GTR than conventional group. The incidence of PLD was 13.4% in multimodal group, which was much lower than that (27.6%, P<0.001) in conventional group. Three factors were associated with TLD, including SDLA (OR=0.85, P<0.001), preoperative AQ (OR=1.04, P<0.001) and multimodal techniques used (OR=0.41, P<0.001). Four factors were associated with PLD, including SDLA (OR=0.83, P=0.001), SMA/PMA involved (OR=3.04, P=0.007), preoperative AQ (OR=1.03, P=0.002) and multimodal techniques used (OR=0.35, P<0.001). The optimal shortest distance thresholds in detecting the occurrence of TLD/PLD were 1.5 and 4mm respectively. The optimal AQ thresholds in detecting the occurrence of TLD/PLD were 52 and 61 respectively. The cutoff values of the predictive probability for TLD/PLD were 23.7% and 16.1%. The area under ROC curve of predictive models for TLD and PLD were 0.70 (95%CI: 0.65-0.75) and 0.72 (95%CI: 0.66-0.79) respectively.

Conclusion

The use of multimodal techniques can reduce the risk of postoperative TLD/PLD after removing GILAs under general anesthesia. The established predictive model based on clinical variables can predict the probability of occurrence of TLD and PLD, and it had a moderate predictive accuracy.

Reorganization and Plasticity of the Language Network in Patients with Cerebral Gliomas

Language is organized in large-scale networks in the human brain that show a strong potential for flexible interactions and adaptation. Neuroplasticity is the central mechanism that allows such dynamic modulation to changing conditions across the life span and is particularly important for network reorganization after brain lesions. Most studies on language reorganization focused on language recovery after stroke. Yet, a strong degree of adaptive neuroplasticity can also be observed in patients with brain tumors in language-eloquent brain areas. This review discusses key mechanisms for neural reorganization in patients with brain tumors. Our main aim is to elucidate the underlying mechanisms for intra- and interhemispheric plasticity in the language network in these patients. The following reorganization patterns are discussed: 1) Persisting function within the tumor; 2) Reorganization in perilesional regions; 3) Reorganization in a distributed network of the affected hemisphere; 4) Reorganization to the contralesional hemisphere. In this context, we shed light on language-related reorganization patterns in frontal and temporo-parietal areas and discuss their functional relevance. We also address tumor-related changes in structural and functional connectivity between eloquent brain regions. Thereby, we aim to expand the general understanding of the plastic potential of the neural language network and facilitate clinical decision-making processes for effective, function-preserving tumor treatment.

Cortical and white matter anatomy relevant for the lateral and superior approaches to resect intraaxial lesions within the frontal lobe

Despite being associated with high-order neurocognitive functions, the frontal lobe plays an important role in core neurological functions, such as motor and language functions. The aim of this study was to present a neurosurgical perspective of the cortical and subcortical anatomy of the frontal lobe in terms of surgical treatment of intraaxial frontal lobe lesions. We also discuss the results of direct brain mapping when awake craniotomy is performed. Ten adult cerebral hemispheres were prepared for white matter dissection according to the Klingler technique. Intraaxial frontal lobe lesions are approached with a superior or lateral trajectory during awake conditions. The highly eloquent cortex within the frontal lobe is identified within the inferior frontal gyrus (IFG) and precentral gyrus. The trajectory of the approach is mainly related to the position of the lesion in relation to the arcuate fascicle/superior longitudinal fascicle complex and ventricular system. Knowledge of the cortical and subcortical anatomy and its function within the frontal lobe is essential for preoperative planning and predicting the risk of immediate and long-term postoperative deficits. This allows surgeons to properly set the extent of the resection and type of approach during preoperative planning.

Speech and Language Errors during Awake Brain Surgery and Postoperative Language Outcome in Glioma Patients: A Systematic Review

Awake craniotomy with direct electrical stimulation (DES) is the standard treatment for patients with gliomas in eloquent areas. Even though language is monitored carefully during surgery, many patients suffer from postoperative aphasia, with negative effects on their quality of life. Some perioperative factors are reported to influence postoperative language outcome. However, the influence of different intraoperative speech and language errors on language outcome is not clear. Therefore, we investigate this relation. A systematic search was performed in which 81 studies were included, reporting speech and language errors during awake craniotomy with DES and postoperative language outcomes in adult glioma patients up until 6 July 2020. The frequencies of intraoperative errors and language status were calculated. Binary logistic regressions were performed. Preoperative language deficits were a significant predictor for postoperative acute (OR = 3.42, p < 0.001) and short-term (OR = 1.95, p = 0.007) language deficits. Intraoperative anomia (OR = 2.09, p = 0.015) and intraoperative production errors (e.g., dysarthria or stuttering; OR = 2.06, p = 0.016) were significant predictors for postoperative acute language deficits. Postoperatively, the language deficits that occurred most often were production deficits and spontaneous speech deficits. To conclude, during surgery, intraoperative anomia and production errors should carry particular weight during decision-making concerning the optimal onco-functional balance for a given patient, and spontaneous speech should be monitored. Further prognostic research could facilitate intraoperative decision-making, leading to fewer or less severe postoperative language deficits and improvement of quality of life.

Monitoring Cortico-cortical Evoked Potentials Using Only Two 6-strand Strip Electrodes for Gliomas Extending to the Dominant Side of Frontal Operculum During One-step Tumor Removal Surgery

OBJECTIVE

Resection of the dominant side of gliomas extending to the frontal operculum has high risk of severe language dysfunction. Here, we report recording cortico-cortical evoked potentials (CCEP) using only two 6-strand strip electrodes to monitor language-related fibers intraoperatively. We examined whether this simple procedure is useful for removing gliomas extending to the dominant side of frontal operculum.

METHODS

This study included 7 cases of glioma extending to the left frontal operculum. The frontal language area (FLA) was first identified by functional mapping during awake craniotomy. Next, a 6-strand strip electrode was placed on the FLA, while on the temporal side, an electrode was placed so as to slide parallel to the sylvian fissure toward the posterior language area. Electrical stimulation was performed using the electrode on the frontal side, and CCEPs were measured from the electrode on the temporal side.

RESULTS

CCEPs were detected in all cases. Immediately after surgery, all patients demonstrated language dysfunction to varying degree. CCEP decreased to 10% in 1 patient, who recovered language function after 24 months. CCEP decreased slightly 80% in 1, and, in the 5 other cases, CCEPs did not change. These 5 patients soon recovered language function within 2 weeks to 1 month.

CONCLUSIONS

This study confirmed the utility of CCEP monitoring using only two 6-strand strip electrodes during one-step surgery. We believe this simple method helped in monitoring intraoperative language function and predicting its postoperative recovery in patients with gliomas extending to the dominant side of frontal operculum.

White matter alterations in the dorsal attention network contribute to a high risk of unsafe driving in healthy older people

Aim

Healthy older drivers may be at high risk of fatal traffic accidents. Our recent study showed that volumetric alterations in gray matter in the brain regions within the dorsal attention network (DAN) were strongly related to the risk of unsafe driving in healthy older people. However, the relationship between white matter (WM) structural connectivity and driving ability in healthy older people is still unclear.

Methods

We used diffusion tensor imaging to examine the association between microstructural alterations in the DAN and the risk of unsafe driving among healthy older people. We enrolled 32 healthy older individuals aged over 65 years and screened unsafe drivers using an on-road driving test. We then determined the pattern of WM aberrations in unsafe drivers using tract-based spatial statistics.

Results

The analysis demonstrated that unsafe drivers had significantly higher axial diffusivity values in nine WM clusters compared with safe drivers. These results were primarily observed bilaterally in the dorsal superior longitudinal fasciculus, which is involved in the DAN. Furthermore, correlation analyses showed that higher axial diffusivity values in the superior longitudinal fasciculus were associated with lower Trail Making Test A scores within unsafe drivers. This result suggests that functionally, WM microstructural alterations in the DAN are associated with attention problems, which may contribute to the risk of unsafe driving among healthy older people.

Conclusion

Our findings may elucidate the neurobiological mechanisms underlying the increased risk of unsafe driving in healthy older people, potentially facilitating the development of new interventions to prevent fatal accidents.

Brain Functional Imaging Anatomy

Human brain function is an increasingly complex framework that has important implications in clinical medicine. In this review, the anatomy of the most commonly assessed brain functions in clinical neuroradiology, including motor, language, and vision, is discussed. The anatomy and function of the primary and secondary sensorimotor areas are discussed with clinical case examples. Next, the dual stream of language processing is reviewed, as well as its implications in clinical medicine and surgical planning. Last, the authors discuss the striate and extrastriate visual cortex and review the dual stream model of visual processing.

Integrity of the Left Arcuate Fasciculus Segments Significantly Affects Language Performance in Individuals with Acute/Subacute Post-Stroke Aphasia: A Cross-Sectional Diffusion Tensor Imaging Study

Objective: To investigate the correlation between the left arcuate fasciculus (AF) segments and acute/subacute post-stroke aphasia (PSA). Methods: Twenty-six patients underwent language assessment and MRI scanning. The integrity of the AF based on a three-segment model was evaluated using diffusion tensor imaging. All patients were classified into three groups according to the reconstruction of the left AF: completely reconstructed (group A, 8 cases), non-reconstructed (group B, 6 cases), and partially reconstructed (group C, 12 cases). The correlations and intergroup differences in language performance and diffusion indices were comprehensively estimated. Results: A correlation analyses showed that the lesion load of the language areas and diffusion indices on the left AF posterior and long segments was significantly related to some language subsets, respectively. When controlled lesion load was variable, significant correlations between diffusion indices on the posterior and long segments and comprehension, repetition, naming, and aphasia quotient were retained. Multiple comparison tests revealed intergroup differences in diffusion indices on the left AF posterior and long segments, as well as these language subsets. No significant correlation was found between the anterior segment and language performance. Conclusions: The integrity of the left AF segments, particularly the posterior segment, is crucial for the residual comprehension and repetition abilities in individuals with acute/subacute PSA, and lesion load in cortical language areas is an important factor that should be taken into account when illustrating the contributions of damage to special fiber tracts to language impairments.

Understanding Language Reorganization With Neuroimaging: How Language Adapts to Different Focal Lesions and Insights Into Clinical Applications

When the language-dominant hemisphere is damaged by a focal lesion, the brain may reorganize the language network through functional and structural changes known as adaptive plasticity. Adaptive plasticity is documented for triggers including ischemic, tumoral, and epileptic focal lesions, with effects in clinical practice. Many questions remain regarding language plasticity. Different lesions may induce different patterns of reorganization depending on pathologic features, location in the brain, and timing of onset. Neuroimaging provides insights into language plasticity due to its non-invasiveness, ability to image the whole brain, and large-scale implementation. This review provides an overview of language plasticity on MRI with insights for patient care. First, we describe the structural and functional language network as depicted by neuroimaging. Second, we explore language reorganization triggered by stroke, brain tumors, and epileptic lesions and analyze applications in clinical diagnosis and treatment planning. By comparing different focal lesions, we investigate determinants of language plasticity including lesion location and timing of onset, longitudinal evolution of reorganization, and the relationship between structural and functional changes.

Controversy over the temporal cortical terminations of the left arcuate fasciculus: a reappraisal

The arcuate fasciculus has been considered a major dorsal fronto-temporal white matter pathway linking frontal language production regions with auditory perception in the superior temporal gyrus, the so-called Wernicke's area. In line with this tradition, both historical and contemporary models of language function have assigned primacy to superior temporal projections of the arcuate fasciculus. However, classical anatomical descriptions and emerging behavioural data are at odds with this assumption. On one hand, fronto-temporal projections to Wernicke's area may not be unique to the arcuate fasciculus. On the other hand, dorsal stream language deficits have been reported also for damage to middle, inferior and basal temporal gyri which may be linked to arcuate disconnection. These findings point to a reappraisal of arcuate projections in the temporal lobe. Here, we review anatomical and functional evidence regarding the temporal cortical terminations of the left arcuate fasciculus by incorporating dissection and tractography findings with stimulation data using cortico-cortical evoked potentials and direct electrical stimulation mapping in awake patients. Firstly, we discuss the fibers of the arcuate fasciculus projecting to the superior temporal gyrus and the functional rostro-caudal gradient in this region where both phonological encoding and auditory-motor transformation may be performed. Caudal regions within the temporoparietal junction may be involved in articulation and associated with temporoparietal projections of the third branch of the superior longitudinal fasciculus, while more rostral regions may support encoding of acoustic phonetic features, supported by arcuate fibres. We then move to examine clinical data showing that multimodal phonological encoding is facilitated by projections of the arcuate fasciculus to superior, but also middle, inferior and basal temporal regions. Hence, we discuss how projections of the arcuate fasciculus may contribute to acoustic (middle-posterior superior and middle temporal gyri), visual (posterior inferior temporal/fusiform gyri comprising the visual word form area) and lexical (anterior-middle inferior temporal/fusiform gyri in the basal temporal language area) information in the temporal lobe to be processed, encoded and translated into a dorsal phonological route to the frontal lobe. Finally, we point out surgical implications for this model in terms of the prediction and avoidance of neurological deficit.

The third branch of the superior longitudinal system

One of the major associative fiber pathways in the brain is the superior longitudinal system. This review discusses the current knowledge gained from studies on the third branch of the superior longitudinal system (SLS) regarding its anatomy, functional role in healthy individuals, results from lesion-symptom mapping studies and intraoperative electrostimulation studies. The results of these studies clearly indicate that the third branch of the SLS is a distinct pathway, as seen both from a functional and anatomical perspective. The third branch of the SLS should be distinguished from the long segment of the arcuate fasciculus, that courses along its trajectory but seems implicated in different functions. Moreover, these studies also provide substantial evidence that the right and left third branch of the SLS have different functional roles. Finally, a hypothesis for an integrated anatomo-functional model is proposed, that describes three subcomponents of the third branch of the superior longitudinal system.

Awake Surgery for Left Posterior Insular Low-Grade Glioma Through the Parietorolandic Operculum: The Need to Preserve the Functional Connectivity. A Case Series

Objective: Surgical approach to low-grade glioma (LGG) involving the posterior insula is challenging, especially in the left hemisphere, with a high risk of sensorimotor, language, or visual deterioration. In this study, a case series of 5 right-handed patients harboring a left posterior insular LGG is reported, by detailing a transcorticosubcortical approach.

Method: The five surgeries were achieved in awake patients using cortical and axonal electrostimulation mapping. The glioma was removed through the left rolandic and/or parietal opercula, with preservation of the subcortical connectivity.

Results: The cortical mapping was positive in the five patients, enabling the selection of an optimal transcortical approach, via the anterolateral supramarginal gyrus in four patients and/or via the lateral retrocentral gyrus in three cases (plus through the left superior temporal gyrus in one case). Moreover, the white matter tracts were identified in all cases, i.e., the lateral part of the superior longitudinal fasciculus (five cases), the arcuate fasciculus (four cases), the thalamocortical somatosensory pathways (four cases), the motor pathway (one case), the semantic pathway (three cases), and the optic tract (one case). Complete resection of the LGG was achieved in two patients and near-total resection in three patients. There were no postoperative permanent sensorimotor, language, or visual deficits.

Conclusion: A transcortical approach through the parietorolandic operculum in awake patients represents safe and effective access to the left posterior insular LGG. Detection and preservation of the functional connectivity using direct electrostimulation of the white matter bundles are needed in this cross-road brain region to prevent otherwise predictable postsurgical impairments.

Simultaneous Damage of the Cingulate Cortex Zone II and Fronto-Striatal Circuit Causes Prolonged Selective Attentional Deficits

Selective attention is essential for successful cognitive performance. Although several brain areas are known to be involved in selective attention, damage to some of these areas does not necessarily cause attentional deficits. In the current study, we hypothesized that damage to specific parts of the right cerebral hemisphere, especially the cingulate cortex (CC), causes prolonged selective attentional deficits, and examined the influence of focal brain damage on selective attention. We recruited 36 patients with right cerebral hemispheric WHO grade 2 and 3 brain tumors who underwent surgery. We assessed selective attention over time from pre-operation to 3 months postoperatively using the cancelation test and color Stroop test, and calculated the percentage of deficit. Additionally, two types of imaging analyses were performed: voxel-based lesion symptom mapping (VLSM) and multiple logistic regression analysis, to reveal related brain regions for selective attention. Consequently, we found that the CC and deep part of the middle frontal gyrus were associated with deficits in selective attention via VLSM. Using multiple logistic regression analysis, the CC zone II at the cortical level (p < 0.0001) and the fronto-striatal tract (FST) at the subcortical level (p = 0.0079) were associated with attentional deficit among several regions identified in the VLSM. At 3 months postoperatively, selective attention was impaired in patients who underwent resection of these regions. Moreover, only patients with simultaneous damage of the CC zone II and FST had prolonged attentional deficits until the chronic phase. Our results suggest that the right CC zone II and FST are critical areas for the selective attentional networks.

Functional Approaches to the Surgery of Brain Gliomas

In the surgery of gliomas, recent years have witnessed unprecedented theoretical and technical development, which extensively increased indication to surgery. On one hand, it has been solidly demonstrated the impact of gross total resection on life expectancy. On the other hand, the paradigm shift from classical cortical localization of brain function towards connectomics caused by the resurgence of awake surgery and the advent of tractography has permitted safer surgeries focused on subcortical white matter tracts preservation and allowed for surgical resections within regions, such as Broca's area or the primary motor cortex, which were previously deemed inoperable. Furthermore, new asleep electrophysiological techniques have been developed whenever awake surgery is not an option, such as operating in situations of poor compliance (including paediatric patients) or pre-existing neurological deficits. One such strategy is the use of intraoperative neurophysiological monitoring (IONM), enabling the identification and preservation of functionally defined, but anatomically ambiguous, cortico-subcortical structures through mapping and monitoring techniques. These advances tie in with novel challenges, specifically risk prediction and the impact of neuroplasticity, the indication for tumour resection beyond visible borders, or supratotal resection, and most of all, a reappraisal of the importance of the right hemisphere from early psychosurgery to mapping and preservation of social behaviour, executive control, and decision making.Here we review current advances and future perspectives in a functional approach to glioma surgery.

Language assessment in awake brain surgery: the Portuguese adaptation of the Dutch linguistic intraoperative protocol (DuLIP)

Awake brain surgery, combined with neurophysiological evaluation and intraoperative mapping, is one of the preferential lines of treatment when approaching low-grade gliomas. Speech and language assessment is used while applying Direct Electrical Stimulation (DES) and during the resection of a lesion/tumour, as it allows to establish related eloquent areas and optimise the extent of the resection and avoid impairments. Patients need to be assessed pre, intra and post-surgery, but in under resourced countries such as Portugal, there are still no standardised and validated tools to conduct this type of evaluation. To address this need, the tasks of the Dutch Linguistic Intraoperative Protocol (DuLIP) were adapted to European Portuguese, and the resulting materials were standardised for a group of 144 Portuguese participants. For each task, the impact of age, gender and schooling were measured. The resulting Portuguese version of the DuLIP (DuLIP-EP) consists of 17 tasks, including phonological, syntactic, semantic, naming and articulatory tests. No significant differences were found between male and female participants. However, schooling influenced phonological and syntactic fluency, object naming and verb generation. Schooling and age had a significant impact on semantic fluency and reading with semantic odd word out tasks. This is the first contribution to the standardisation of a tool that can be used during an awake brain surgery in Portugal, which includes a new phonological odd word out task that is not currently available in the Dutch version.

Tumor location-based classification of surgery-related language impairments in patients with glioma

INTRODUCTION

Many patients with glioma experience surgery-related language impairment. This study developed a classification system to predict postoperative language prognosis.

METHODS

Sixty-eight patients were retrospectively reviewed. Based on their location, tumors were subtyped as follows: (I) inferior frontal lobe or precentral gyrus; (II) posterior central gyrus or supramarginal gyrus (above the lateral fissure level); (III) posterior region of the superior or middle temporal gyri or supramarginal gyrus (below the lateral fissure level); and (IV) insular lobe. The distance from the tumor to the superior longitudinal fasciculus/arcuate fasciculus was calculated. The recovery of language function was assessed using the Western Aphasia Battery before surgery, and a comprehensive language test was conducted on the day of surgery; 3, 7, and 14 days after surgery. Our follow-up information of was the comprehensive language test from telephone interviews in 3 months after surgery.

RESULTS

Thirty-three patients experienced transient language impairment within 1 week of surgery. Fourteen patients had permanent language impairment. Type II tumors, shorter distance from the tumor to the posterior superior longitudinal fasciculus/arcuate fasciculus, and isocitrate dehydrogenase mutations were risk factors for surgery-related language impairment. Regarding the presence or absence of permanent surgery-related language impairments, the cut-off distance between the tumor and posterior superior longitudinal fasciculus/arcuate fasciculus was 2.75 mm.

CONCLUSIONS

According to our classification, patients with type II tumors had the worst language prognosis and longest recovery time. Our classification, based on tumor location, can reliably predict postoperative language status and may be used to guide tumor resection.

The death of localizationism: The concepts of functional connectome and neuroplasticity deciphered by awake mapping, and their implications for best care of brain-damaged patients

Although clinical neurology was mainly erected on the dogma of localizationism, numerous reports have described functional recovery after lesions involving presumed non-compensable areas in an inflexible view of brain processing. Here, the purpose is to review new insights into the functional connectome and the mechanisms underpinning neural plasticity, gained from intraoperative direct electrostimulation mapping and real-time behavioral monitoring in awake patients, combined with perioperative neuropsychological and neuroimaging data. Such longitudinal anatomo-functional correlations resulted in the reappraisal of classical models of cognition, especially by highlighting the dynamic interplay within and between neural circuits, leading to the concept of meta-network (network of networks), as well as by emphasizing that subcortical connectivity is the main limitation of neuroplastic potential. Beyond their contribution to basic neurosciences, these findings might also be helpful for an optimization of care for brain-damaged patients, such as in resective oncological or epilepsy neurosurgery in structures traditionally deemed inoperable (e.g., in Broca's area) as well as for elaborating new programs of functional rehabilitation, eventually combined with transcranial brain stimulation, aiming to change the connectivity patterns in order to enhance cognitive competences following cerebral injury.

Intra-operative mapping and language protection in glioma

ABSTRACT

The demand for acquiring different languages has increased with increasing globalization. However, knowledge of the modification of the new language in the neural language network remains insufficient. Although many details of language function have been detected based on the awake intra-operative mapping results, the language neural network of the bilingual or multilingual remains unclear, which raises difficulties in clinical practice to preserve patients' full language ability in neurosurgery. In this review, we present a summary of the current findings regarding the structure of the language network and its evolution as the number of acquired languages increased in glioma patients. We then discuss a new insight into the awake intra-operative mapping protocol to reduce surgical risks during the preservation of language function in multilingual patients with glioma.

Damage to Broca's area does not contribute to long-term speech production outcome after stroke

Broca's area in the posterior half of the left inferior frontal gyrus has long been thought to be critical for speech production. The current view is that long-term speech production outcome in patients with Broca's area damage is best explained by the combination of damage to Broca's area and neighbouring regions including the underlying white matter, which was also damaged in Paul Broca's two historic cases. Here, we dissociate the effect of damage to Broca's area from the effect of damage to surrounding areas by studying long-term speech production outcome in 134 stroke survivors with relatively circumscribed left frontal lobe lesions that spared posterior speech production areas in lateral inferior parietal and superior temporal association cortices. Collectively, these patients had varying degrees of damage to one or more of nine atlas-based grey or white matter regions: Brodmann areas 44 and 45 (together known as Broca's area), ventral premotor cortex, primary motor cortex, insula, putamen, the anterior segment of the arcuate fasciculus, uncinate fasciculus and frontal aslant tract. Spoken picture description scores from the Comprehensive Aphasia Test were used as the outcome measure. Multiple regression analyses allowed us to tease apart the contribution of other variables influencing speech production abilities such as total lesion volume and time post-stroke. We found that, in our sample of patients with left frontal damage, long-term speech production impairments (lasting beyond 3 months post-stroke) were solely predicted by the degree of damage to white matter, directly above the insula, in the vicinity of the anterior part of the arcuate fasciculus, with no contribution from the degree of damage to Broca's area (as confirmed with Bayesian statistics). The effect of white matter damage cannot be explained by a disconnection of Broca's area, because speech production scores were worse after damage to the anterior arcuate fasciculus with relative sparing of Broca's area than after damage to Broca's area with relative sparing of the anterior arcuate fasciculus. Our findings provide evidence for three novel conclusions: (i) Broca's area damage does not contribute to long-term speech production outcome after left frontal lobe strokes; (ii) persistent speech production impairments after damage to the anterior arcuate fasciculus cannot be explained by a disconnection of Broca's area; and (iii) the prior association between persistent speech production impairments and Broca's area damage can be explained by co-occurring white matter damage, above the insula, in the vicinity of the anterior part of the arcuate fasciculus.

New Philosophy, Clinical Pearls, and Methods for Intraoperative Cognition Mapping and Monitoring "à la carte" in Brain Tumor Patients

The purpose of surgery for brain tumors involving eloquent neural circuits is to maximize the extent of resection while preserving an optimal quality of life. To this end, especially in diffuse glioma, the goal is to remove the cerebral parenchyma invaded by the neoplasm up to the individual cortico-subcortical networks critical for brain functions. Intraoperative mapping combined with real-time cognitive monitoring throughout the resection in awake patient is thus highly recommended to resume a normal life. Indeed, beyond avoiding hemiplegia or aphasia, enjoying a familial, social, and professional life implies that motor and language mapping is not sufficient. Identifying and sparing neural networks that subserve cognition (movement control, visuospatial cognition, executive functions, multimodal semantics, metacognition) and mentalizing (theory of mind, which plays a key role for social cognition) is essential to preserve an adapted behavior. Here, the aim is to review when and how to map these critical functions, which have nonetheless been neglected for many decades by neurosurgeons. In fact, the disorders generated by surgical injuries of circuits underpinning nonmotor and nonspeech functions are usually not immediately visible on postoperative standard clinical examination, leading the physician to believe that the patient has no deficit. Yet, cognitive or emotional disturbances may subsequently prevent to resume an active life, as to work full time. Therefore, a systematic neuropsychological assessment should be performed before, during, and after mapping-guided surgery, regardless of the tumor location, to preserve the functional connectome intraoperatively and to plan a postoperative tailored cognitive rehabilitation according to the patient's needs.

Large-scale functional brain networks for consciousness

The generation and maintenance of consciousness are fundamental but difficult subjects in the fields of psychology, philosophy, neuroscience, and medicine. However, recent developments in neuro-imaging techniques coupled with network analysis have greatly advanced our understanding of consciousness. The present review focuses on large-scale functional brain networks based on neuro-imaging data to explain the awareness (contents) and wakefulness of consciousness. Despite limitations, neuroimaging data suggests brain maps for important psychological and cognitive processes such as attention, language, self-referential, emotion, motivation, social behavior, and wakefulness. We considered a review of these advancements would provide new insights into research on the neural correlates of consciousness.

Intraoperative Corticocortical Evoked Potentials for Language Monitoring in Epilepsy Surgery

OBJECTIVE

To evaluate the applicability of corticocortical evoked potentials (CCEP) for intraoperative monitoring of the language network in epilepsy surgery under general anesthesia. To investigate the clinical relevance on language functions of intraoperative changes of CCEP recorded under these conditions.

METHODS

CCEP monitoring was performed in 14 epileptic patients (6 females, 4 children) during resections in the left perisylvian region under general anesthesia. Electrode strips were placed on the anterior language area (AL) and posterior language area (PL), identified by structural and functional magnetic resonance imaging. Single-pulse electric stimulations were delivered to pairs of adjacent contacts in a bipolar fashion. During resection, we monitored the integrity of the dorsal language pathway by stimulating either AL by recording CCEP from PL or vice versa, depending on stability and reproducibility of CCEP. We evaluated the first negative (N1) component of CCEP before, during, and after resection.

RESULTS

All procedures were successfully completed without adverse events. The best response was obtained from AL during stimulation of PL in 8 patients and from PL during stimulation of AL in 6 patients. None of 12 patients with a postresection N1 amplitude decrease of 0%-15% from baseline presented postoperative language impairment. Decreases of 28% and 24%, respectively, of the N1 amplitude were observed in 2 patients who developed transient postoperative speech disturbances.

CONCLUSIONS

The application of CCEP monitoring is possible and safe in epilepsy surgery under general anesthesia. Putative AL and PL can be identified using noninvasive presurgical neuroimaging. Decrease of N1 amplitude >15% from baseline may predict postoperative language deficits.

The superior longitudinal fascicle: reconsidering the fronto-parietal neural network based on anatomy and function

Due primarily to the extensive disposition of fibers and secondarily to the methodological preferences of researchers, the superior longitudinal fasciculus (SLF) subdivisions have multiple names, complicating SLF research. Here, we collected and reassessed existing knowledge regarding the SLF, which we used to propose a four-term classification of the SLF based mainly on function: dorsal SLF, ventral SLF, posterior SLF, and arcuate fasciculus (AF); these correspond to the traditional SLF II, SLF III or anterior AF, temporoparietal segment of the SLF or posterior AF, and AF or AF long segment, respectively. Each segment has a distinct functional role. The dorsal SLF is involved in visuospatial attention and motor control, while the ventral SLF is associated with language-related networks, auditory comprehension, and articulatory processing in the left hemisphere. The posterior SLF is involved in language-related processing, including auditory comprehension, reading, and lexical access, while the AF is associated with language-related activities, such as phonological processing; the right AF plays a role in social cognition and visuospatial attention. This simple proposed classification permits a better understanding of the SLF and may comprise a convenient classification for use in research and clinical practice relating to brain function.

Middle Frontal Gyrus and Area 55b: Perioperative Mapping and Language Outcomes

Background: The simplistic approaches to language circuits are continuously challenged by new findings in brain structure and connectivity. The posterior middle frontal gyrus and area 55b (pFMG/area55b), in particular, has gained a renewed interest in the overall language network.

Methods: This is a retrospective single-center cohort study of patients who have undergone awake craniotomy for tumor resection. Navigated transcranial magnetic simulation (nTMS), tractography, and intraoperative findings were correlated with language outcomes.

Results: Sixty-five awake craniotomies were performed between 2012 and 2020, and 24 patients were included. nTMS elicited 42 positive responses, 76.2% in the inferior frontal gyrus (IFG), and hesitation was the most common error (71.4%). In the pMFG/area55b, there were seven positive errors (five hesitations and two phonemic errors). This area had the highest positive predictive value (43.0%), negative predictive value (98.3%), sensitivity (50.0%), and specificity (99.0%) among all the frontal gyri. Intraoperatively, there were 33 cortical positive responses—two (6.0%) in the superior frontal gyrus (SFG), 15 (45.5%) in the MFG, and 16 (48.5%) in the IFG. A total of 29 subcortical positive responses were elicited−21 in the deep IFG–MFG gyri and eight in the deep SFG–MFG gyri. The most common errors identified were speech arrest at the cortical level (20 responses−13 in the IFG and seven in the MFG) and anomia at the subcortical level (nine patients—eight in the deep IFG–MFG and one in the deep MFG–SFG). Moreover, 83.3% of patients had a transitory deterioration of language after surgery, mainly in the expressive component (p = 0.03). An increased number of gyri with intraoperative positive responses were related with better preoperative (p = 0.037) and worse postoperative (p = 0.029) outcomes. The involvement of the SFG–MFG subcortical area was related with worse language outcomes (p = 0.037). Positive nTMS mapping in the IFG was associated with a better preoperative language outcome (p = 0.017), relating to a better performance in the expressive component, while positive mapping in the MFG was related to a worse preoperative receptive component of language (p = 0.031).

Conclusion: This case series suggests that the posterior middle frontal gyrus, including area 55b, is an important integration cortical hub for both dorsal and ventral streams of language.

Preoperative transcranial magnetic stimulation for picture naming is reliable in mapping segments of the arcuate fasciculus

In preoperative planning for neurosurgery, both anatomical (diffusion imaging tractography) and functional tools (MR-navigated transcranial magnetic stimulation) are increasingly used to identify and preserve eloquent language structures specific to individuals. Using these tools in healthy adults shows that speech production errors occur mainly in perisylvian cortical sites that correspond to subject-specific terminations of the major language pathway, the arcuate fasciculus. It is not clear whether this correspondence remains in oncological patients with altered tissue. We studied a heterogeneous cohort of 30 patients (fourteen male, mean age 44), undergoing a first or second surgery for a left hemisphere brain tumour in a language-eloquent region, to test whether speech production errors induced by preoperative transcranial magnetic stimulation had consistent anatomical correspondence to the arcuate fasciculus. We used navigated repetitive transcranial magnetic stimulation during picture naming and recorded different perisylvian sites where transient interference to speech production occurred. Spherical deconvolution diffusion imaging tractography was performed to map the direct fronto-temporal and indirect (fronto-parietal and parieto-temporal) segments of the arcuate fasciculus in each patient. Speech production errors were reported in all patients when stimulating the frontal lobe, and in over 90% of patients in the parietal lobe. Errors were less frequent in the temporal lobe (54%). In all patients, at least one error site corresponded to a termination of the arcuate fasciculus, particularly in the frontal and parietal lobes, despite distorted anatomy due to a lesion and/or previous resection. Our results indicate that there is strong correspondence between terminations of the arcuate fasciculus and speech errors. This indicates that white matter anatomy may be a robust marker for identifying functionally eloquent cortex, particularly in the frontal and parietal lobe. This knowledge may improve targets for preoperative mapping of language in the neurosurgical setting.

Ventral Precentral Fiber Intersection Area: A Central Hub in the Connectivity of Perisylvian Associative Tracts

BACKGROUND

The ventral part of the precentral gyrus is considered one of the most eloquent areas. However, little is known about the white matter organization underlying this functional hub.

OBJECTIVE

To analyze the subcortical anatomy underlying the ventral part of the precentral gyrus, ie, the ventral precentral fiber intersection area (VPFIA).

METHODS

Eight human hemispheres from cadavers were dissected, and 8 healthy hemispheres were studied with diffusion tensor imaging tractography. The tracts that terminate at the ventral part of the precentral gyrus were isolated. In addition, 6 surgical cases with left side gliomas close to the VPFIA were operated awake with intraoperative electrical stimulation mapping.

RESULTS

The connections within the VPFIA are anatomically organized along an anteroposterior axis: the pyramidal pathway terminates at the anterior bank of the precentral gyrus, the intermediate part is occupied by the long segment of the arcuate fasciculus, and the posterior bank is occupied by the anterior segment of the arcuate fasciculus. Stimulation of the VPFIA elicited speech arrest in all cases.

CONCLUSION

The present study shows strong arguments to sustain that the fiber organization of the VPFIA is different from the classical descriptions, bringing new light for understanding the functional role of this area in language. The VPFIA is a critical neural epicenter within the perisylvian network that may represent the final common network for speech production, as it is strategically located between the termination of the dorsal stream and the motor output cortex that directly control speech muscles.

Direct Evidence of Plasticity within Human Primary Motor and Somatosensory Cortices of Patients with Glioblastoma

Glioblastoma multiforme (GBM) is a devastating disease without cure. It is also the most common primary brain tumor in adults. Although aggressive surgical resection is standard of care, these operations are limited by tumor infiltration of critical cortical and subcortical regions. A better understanding of how the brain can recover and reorganize function in response to GBM would provide valuable clinical data. This ability, termed neuroplasticity, is not well understood in the adult human brain. A better understanding of neuroplasticity in GBM could allow for improved extent of resection, even in areas classically thought to have critical, static function. The best evidence to date has demonstrated neuroplasticity only in slower growing tumors or through indirect measures such as functional MRI or transcranial magnetic stimulation. In this novel study, we utilize a unique experimental paradigm to show direct evidence of plasticity via serial direct electrocortical stimulation (DES) within primary motor (M1) and somatosensory (S1) cortices in GBM patients. Six patients with glioblastoma multiforme in or near the primary motor or somatosensory cortex were included in this retrospective observational study. These patients had two awake craniotomies with DES to map cortical motor and sensory sites in M1 and S1. Five of six patients exhibited at least one site of neuroplasticity within M1 or S1. Out of the 51 total sites stimulated, 32 (62.7%) demonstrated plasticity. Of these sites, 14 (43.7%) were in M1 and 18 (56.3%) were in S1. These data suggest that even in patients with GBM in or near primary brain regions, significant functional reorganization is possible. This is a new finding which may lead to a better understanding of the fundamental factors promoting or inhibiting plasticity. Further exploration may aid in treatment of patients with brain tumors and other neurologic disorders.

What do we know about pre- and postoperative plasticity in patients with glioma? A review of neuroimaging and intraoperative mapping studies

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Brain reorganization can take place before and after surgery of low- and high-grade gliomas.

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Plasticity is observed for low-grade but also for high-grade gliomas.

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The contralesional hemisphere can be vital for successful compensation.

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There is evidence of plasticity for both the language system and the sensorimotor system.

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Partial compensation can also occur at the white-matter level.

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Subcortical connectivity is crucial for brain reorganization.

Brain plasticity potential is a central theme in neuro-oncology and is currently receiving increased attention. Advances in treatment have prolonged life expectancy in neuro-oncological patients and the long-term preservation of their quality of life is, therefore, a new challenge. To this end, a better understanding of brain plasticity mechanisms is vital as it can help prevent permanent deficits following neurosurgery.

Indeed, reorganization processes can be fundamental to prevent or recover neurological and cognitive deficits by reallocating brain functions outside the lesioned areas. According to more recent studies in the literature, brain reorganization taking place following neurosurgery is associated with good neurofunctioning at follow-up. Interestingly, in the last few years, the number of reports on plasticity has notably increased.

Aim of the current review was to provide a comprehensive overview of pre- and postoperative neuroplasticity patterns. Within this framework, we aimed to shed light on some tricky issues, including i) involvement of the contralateral healthy hemisphere, ii) role and potential changes of white matter and connectivity patterns, and iii) reorganization in low- versus high-grade gliomas.

We finally discussed the practical implications of these aspects and role of additional potentially relevant factors to be explored. Final purpose was to provide a guideline helpful in promoting increase in the extent of tumor resection while preserving the patients’ neurological and cognitive functioning.

Why brain radiation therapy should take account of the individual structural and functional connectivity: Toward an irradiation "à la carte"

Although radiation therapy (RT) is a main treatment of brain tumors, delayed cerebral toxicity may lead to cognitive deteriorations with adverse effects on quality of life. Despite technological advances in RT, the concept of brain connectome has not yet been incorporated in the strategy of irradiation. Because white matter tracts represent the main limitation of neuroplasticity, tumor surgery is increasingly performed with awake cortical-subcortical mapping. Here, the purpose is to reinforce the link between cognitive neurosciences and neurooncology, which is critical for neurosurgeons but also for medical oncologists, especially brain radiation oncologists. The goal is to optimize RT planning by sparing individual critical neural networks. A redefinition of "organs at risk" should be proposed, beyond the few structures (such as brainstem, optic pathway, pituitary gland, hippocampi) which are classically preserved for brain radiation, by considering the structural and functional connectivity in order to evolve toward a RT "à la carte".

Revisiting the Functional Anatomy of the Human Brain: Toward a Meta-Networking Theory of Cerebral Functions

For more than one century, brain processing was mainly thought in a localizationist framework, in which one given function was underpinned by a discrete, isolated cortical area, and with a similar cerebral organization across individuals. However, advances in brain mapping techniques in humans have provided new insights into the organizational principles of anatomo-functional architecture. Here, we review recent findings gained from neuroimaging, electrophysiological, as well as lesion studies. Based on these recent data on brain connectome, we challenge the traditional, outdated localizationist view and propose an alternative meta-networking theory. This model holds that complex cognitions and behaviors arise from the spatiotemporal integration of distributed but relatively specialized networks underlying conation and cognition (e.g., language, spatial cognition). Dynamic interactions between such circuits result in a perpetual succession of new equilibrium states, opening the door to considerable interindividual behavioral variability and to neuroplastic phenomena. Indeed, a meta-networking organization underlies the uniquely human propensity to learn complex abilities, and also explains how postlesional reshaping can lead to some degrees of functional compensation in brain-damaged patients. We discuss the major implications of this approach in fundamental neurosciences as well as for clinical developments, especially in neurology, psychiatry, neurorehabilitation, and restorative neurosurgery.

A probabilistic map of negative motor areas of the upper limb and face: a brain stimulation study

Negative motor responses (NMRs) are defined as movement arrests induced by direct electrical stimulation of the brain. The NMRs manifest themselves after the disruption of a corticosubcortical network involved in motor control, referred to as the 'negative motor network'. At present, the spatial topography of the negative motor areas (NMAs) is poorly known. Hence, the objectives of the present study were to establish the first probabilistic map of the NMAs of the upper limbs and face, identify potential subareas, and investigate the NMAs' relationships with the primary motor cortex. A total of 117 patients with low grade glioma underwent awake surgery with direct electrostimulation. The Montreal Neurological Institute coordinates of sites eliciting NMRs (face and upper limbs) were registered. A probabilistic map was created, and subareas were identified in a cluster analysis. Each cluster was then plotted on the Glasser atlas and the 1200 Subjects Group Average Data from the Human Connectome Project, in order to study connectivity and compare the results with recent parcellation data. We elicited 386 NMRs (mean ± standard deviation current intensity: 2.26 ± 0.5 mA) distributed throughout the precentral gyrus in both hemispheres. In each hemisphere, we found two clusters for facial NMRs. For upper limb NMRs, we found two clusters in the right hemisphere; and three in the left. Each cluster overlapped with parcellations from the Glasser atlas. For the face, the NMAs were associated with areas 55b and 6v. For the upper limbs, the NMAs were linked to areas 6v, 6d, and 55b. Each NMA cluster showed a specific pattern of functionally connected areas, such as the inferior frontal gyrus, supplementary motor area, parietal areas, and posterior superior temporal gyrus. The white matter pathways projecting to these subareas involved the frontal aslant tract and the frontostriatal tract-both of which are well known to be associated with NMRs. This study constitutes the largest series to date of NMRs mapped to the lateral surface of both hemispheres. Rather than being randomly distributed, the NMAs appeared to be well structured and corresponded to parcellations identified by functional neuroimaging. Moreover, the white matter pathways known to drive NMRs are also connected to regions encompassing NMAs. Taken as a whole, our results suggest that NMAs belong to a large-scale modulatory motor network. Our new probabilistic map might constitute a valuable tool for use in further clinical and fundamental studies of motor control.

The white matter architecture underlying semantic processing: A systematic review

From a holistic point of view, semantic processes are subserved by large-scale subcortico-cortical networks. The dynamic routing of information between grey matter structures depends on the integrity of subcortical white matter pathways. Nonetheless, controversy remains on which of these pathways support semantic processing. Therefore, a systematic review of the literature was performed with a focus on anatomo-functional correlations obtained from direct electrostimulation during awake tumor surgery, and conducted between diffusion tensor imaging metrics and behavioral semantic performance in healthy and aphasic individuals. The 43 included studies suggest that the left inferior fronto-occipital fasciculus contributes to the essential connectivity that allows semantic processing. However, it remains uncertain whether its contributive role is limited to the organization of semantic knowledge or extends to the level of semantic control. Moreover, the functionality of the left uncinate fasciculus, inferior longitudinal fasciculus and the posterior segment of the indirect arcuate fasciculus in semantic processing has to be confirmed by future research.

Glioma surgery under awake condition can lead to good independence and functional outcome excluding deep sensation and visuospatial cognition

Background

Awake surgery for the eloquent cortex is a common strategy for glioma surgery. Although a recent emphasis has been placed on awake surgery both for dominant and nondominant cerebral hemispheres to preserve neurological/neuropsychological functions, those functional outcomes are not well investigated because few studies have focused on the longitudinal recovery process. This study explored the outcome of neurological/neuropsychological functions following awake surgery until the chronic phase.

Methods

A total of 87 patients with glioma who underwent awake surgery were included, and of these 66 patients matched our inclusion criteria. Each patient was assessed for neurological/neuropsychological functions before surgery, as well as acute and chronic phase. Additionally, scores for the KPS were collected.

Results

Almost all functions recovered within 3 months postoperatively, even when transient deficits were observed in the acute phase; however, deep sensory perception deficits and visuospatial cognitive disorders persisted into the chronic phase (15.4% of patients with parietal lesions, 14.3% of patients with right cerebral hemispheric lesion, respectively). KPS score ≥90 was achieved in 86.0% of patients with lower-grade glioma, whereas only 52.2% of glioblastoma patients scored ≥90. Primary causes of declined KPS were disorder of visuospatial cognition, sensorimotor function including deep sensation, aphasia, and emotional function.

Conclusions

Awake surgery leads to good functional outcome at the chronic phase of neurological/neuropsychological functions, except for deep sensory and visuospatial cognition. Because sensation and visuospatial cognitive disorder have major impacts on patients' independence level, further importance should be placed on preserving these functions during surgery.

MEG imaging of recurrent gliomas reveals functional plasticity of hemispheric language specialization

In patients with gliomas, changes in hemispheric specialization for language determined by magnetoencephalography (MEG) were analyzed to elucidate the impact of treatment and tumor recurrence on language networks. Demonstration of reorganization of language networks in these patients has significant implications on the prevention of postoperative functional loss and recovery. Whole-brain activity during an auditory verb generation task was estimated from MEG recordings in a group of 73 patients with recurrent gliomas. Hemisphere of language dominance was estimated using the language laterality index (LI), a measure derived from the task. The initial scan was performed prior to resection; patients subsequently underwent surgery and adjuvant treatment. A second scan was performed upon recurrence prior to repeat resection. The relationship between the shift in LI between scans and demographics, anatomic location, pathology, and adjuvant treatment was analyzed. Laterality shifts were observed between scans; the median percent change was 29.1% across all patients. Laterality shift magnitude and relative direction were associated with the initial position of language dominance; patients with increased lateralization experienced greater shifts than those presenting more bilateral representation. A change in LI from left or right to bilateral (or vice versa) occurred in 23.3% of patients; complete switch occurred in 5.5% of patients. Patients with tumors within the language-dominant hemisphere experienced significantly greater shifts than those with contralateral tumors. The majority of patients with glioma experience shifts in language network organization over time which correlate with the relative position of language lateralization and tumor location.

Whole-Brain Network Connectivity Underlying the Human Speech Articulation as Emerged Integrating Direct Electric Stimulation, Resting State fMRI and Tractography

Production of fluent speech in humans is based on a precise and coordinated articulation of sounds. A speech articulation network (SAN) has been observed in multiple brain studies typically using either neuroimaging or direct electrical stimulation (DES), thus giving limited knowledge about the whole brain structural and functional organization of this network. In this study, seven right-handed patients underwent awake surgery resection of low-grade gliomas (4) and cavernous angiomas. We combined pre-surgical resting state fMRI (rs-fMRI) and diffusion MRI together with speech arrest sites obtained intra-operatively with DES to address the following goals: (i) determine the cortical areas contributing to the intrinsic functional SAN using the speech arrest sites as functional seeds for rs-fMRI; (ii) evaluate the relative contribution of gray matter terminations from the two major language dorsal stream bundles, the superior longitudinal fasciculus (SLF III) and the arcuate fasciculus (AF); and (iii) evaluate the possible pre-surgical prediction of SAN with rs-fMRI. In all these right-handed patients the intrinsic functional SAN included frontal, inferior parietal, temporal, and insular regions symmetrically and bilaterally distributed across the two hemispheres regardless of the side (four right) of speech arrest evocation. The SLF III provided a much higher density of terminations in the cortical regions of SAN in respect to AF. Pre-surgical rs-fMRI data demonstrated moderate ability to predict the SAN. The set of functional and structural data provided in this multimodal study characterized, at a whole-brain level, a distributed and bi-hemispherical network subserving speech articulation.

Morphometry of the Hand Knob Region and Motor Function Change in Eloquent Area Glioma Patients

PURPOSE

The hand knob area is the cortical representation of motor hand function. The current study aimed to investigate the effects of eloquent area gliomas on the morphometry of the hand motor cortex and preoperative hand motor function.

METHODS

A retrospective study of 320 glioma patients was conducted. Seventy-eight patients with gliomas involving motor functional area were finally enrolled. Using axial T2-weight magnetic resonance images, the width and height of the hand knob were measured in both hemispheres, and differences were compared between the affected and unaffected hemispheres. Receiver operating characteristic (ROC) curve and logistic regression analysis were used to estimate the degree of correlation between distance measurements and motor impairment.

RESULTS

The width and height of the hand knob in the affected and unaffected hemispheres were significantly different (p < 0.0001). The width, height and distance from the tumor to hand knob were reduced in the functionally impaired group compared to the unimpaired group (p = 0.0003, p < 0.0001, p = 0.0005, respectively). The three parameters were significantly correlated and remained significant in ROC and logistic regression analysis. The optimal cut-off value of width, height and distance for identifying preoperative hand muscle strength were 5.73 mm, 5.80 mm and 5.92 mm, respectively.

CONCLUSION

The morphometry of the hand knob is often changed by the infiltration or extrusion of the tumors that were located in or near the hand knob. The width, height of hand knob and the distance from tumor to hand knob could serve as anatomic biomarkers related to preoperative neurological motor deficits.