Same, Same but Different? A Multi-Method Review of the Processes Underlying Executive Control

Attention, working memory, and executive control are commonly considered distinct cognitive functions with important reciprocal interactions. Yet, longstanding evidence from lesion studies has demonstrated both overlap and dissociation in their behavioural expression and anatomical underpinnings, suggesting that a lower dimensional framework could be employed to further identify processes supporting goal-directed behaviour. Here, we describe the anatomical and functional correspondence between attention, working memory, and executive control by providing an overview of cognitive models, as well as recent data from lesion studies, invasive and non-invasive multimodal neuroimaging and brain stimulation. We emphasize the benefits of considering converging evidence from multiple methodologies centred on the identification of brain mechanisms supporting goal-driven behaviour. We propose that expanding on this approach should enable the construction of a comprehensive anatomo-functional framework with testable new hypotheses, and aid clinical neuroscience to intervene on impairments of executive functions.

Psychological and Psychiatric Aspects of Brain and Spinal Cord Tumors

Central nervous system (CNS) tumors are mainly diagnosed by physical symptoms such as paralysis, visual field defect, seizure, and loss of consciousness. The psychological and psychiatric background of CNS tumors, whether in preoperative or postoperative period, has long been a neglected topic; however, lately, many authors and researchers have paid more attention to these manifestations. Neurocognition is a subset of parameters, including attention, memory, mood, emotions, language production, personality, executive function, problem-solving, calculation, and spatial cognition, making up the patient's cognitive performance. Also, it is worthy to say that neurocognition is considered a parameter of quality of life (QoL). Currently, we know that neurocognitive disorders are a group of symptoms presenting by the patients. These symptoms may be the first picture of CNS lesions, which result in incorrect treatment, a higher financial burden on the patient and health system, and finally, poorer QoL and performance scale if they are not diagnosed early. Psychological and psychiatric problems such as depression, anxiety, and phobia following the CNS tumors have two aspects. These may present before any treatment resulting from the tumoral mass effect, peritumoral edema, or cerebral tissue disruption due to the space-occupying lesion. On the other hand, we can see these features after a kind of therapy such as surgery, medical therapy, or adjuvant therapy. Sometimes, the CNS tumors lead to psychosocial complications postoperatively. Indeed, considering tumor surgery complications, some patients may find various degrees of deficits that make the patient isolated either socially or professionally. Obviously, the improvement rate and outcome of this specific situation depend on the mechanism of occurrence and its causes. For instance, postoperative symptom relief would be expected when the symptoms are related to the tumoral mass effect. Getting familiar with this constellation of the symptoms, realizing them, and then localizing them to the correct area of the CNS are very crucial. Accordingly, because of their importance in QoL, their influence on patient's survival even more than the extent of resection of the tumor, and somehow their ignorance, we will discuss different neurocognitive manifestations related to CNS tumors in this chapter.

Structural connectivity in ventral language pathways characterizes non-verbal autism

Language capacities in autism spectrum disorders (ASD) range from normal scores on standardized language tests to absence of functional language in a substantial minority of 30% of individuals with ASD. Due to practical difficulties of scanning at this severe end of the spectrum, insights from MRI are scarce. Here we used manual deterministic tractography to investigate, for the first time, the integrity of the core white matter tracts defining the language connectivity network in non-verbal ASD (nvASD): the three segments of the arcuate (AF), the inferior fronto-occipital (IFOF), the inferior longitudinal (ILF) and the uncinate (UF) fasciculi, and the frontal aslant tract (FAT). A multiple case series of nine individuals with nvASD were compared to matched individuals with verbal ASD (vASD) and typical development (TD). Bonferroni-corrected repeated measure ANOVAs were performed separately for each tract-Hemisphere (2:Left/Right) × Group (3:TD/vASD/nvASD). Main results revealed (i) a main effect of group consisting in a reduction in fractional anisotropy (FA) in the IFOF in nvASD relative to TD; (ii) a main effect of group revealing lower values of radial diffusivity (RD) in the long segment of the AF in nvASD compared to vASD group; and (iii) a reduced volume in the left hemisphere of the UF when compared to the right, in the vASD group only. These results do not replicate volumetric differences of the dorsal language route previously observed in nvASD, and instead point to a disruption of the ventral language pathway, in line with semantic deficits observed behaviourally in this group.

The Role of the Dorsolateral Prefrontal Cortex for Speech and Language Processing

This review article summarizes various functions of the dorsolateral prefrontal cortex (DLPFC) that are related to language processing. To this end, its connectivity with the left-dominant perisylvian language network was considered, as well as its interaction with other functional networks that, directly or indirectly, contribute to language processing. Language-related functions of the DLPFC comprise various aspects of pragmatic processing such as discourse management, integration of prosody, interpretation of nonliteral meanings, inference making, ambiguity resolution, and error repair. Neurophysiologically, the DLPFC seems to be a key region for implementing functional connectivity between the language network and other functional networks, including cortico-cortical as well as subcortical circuits. Considering clinical aspects, damage to the DLPFC causes psychiatric communication deficits rather than typical aphasic language syndromes. Although the number of well-controlled studies on DLPFC language functions is still limited, the DLPFC might be an important target region for the treatment of pragmatic language disorders.

The inferior fronto-occipital fascicle: a century of controversies from anatomy theaters to operative neurosurgery

INTRODUCTION

Since its first description in the early 19th century, the inferior frontooccipital fascicle (IFOF) and its anatomo-functional features were neglected in the neuroscientific literature for the last century. In the last decade, the rapid development of in vivo imaging for the reconstruction of white matter (WM) connectivity (i.e., tractography) and the consequent interest in more traditional ex vivo methods (postmortem dissection) have allowed a renewed debate about course, termination territories, anatomical relationships, and functional roles of this fascicle.

EVIDENCE ACQUISITION

We reviewed the main current knowledge concerning the structural and functional anatomy of the IFOF and possible implications in neurosurgical practice.

EVIDENCE SYNTHESIS

The IFOF connects the occipital cortex, the temporo-basal areas, the superior parietal lobule, and the pre-cuneus to the frontal lobe, passing through the ventral third of subinsular WM of the external capsule. This wide distribution of cortical terminations provides multimodal integration between several functional networks, including language, non-verbal semantic processing, object identification, visuo-spatial processing and planning, reading, facial expression recognition, memory and conceptualization, emotional and neuropsychological behavior. This anatomo-functional organization has important implication also in neurosurgical practice, especially when approaching the frontal, insular, temporo-parieto-occipital regions and the ventricular system.

CONCLUSIONS

The IFOF is the most extensive associative bundle of the human connectome. Its multi-layer organization reflects important implications in many aspects of brain functional processing. Accurate awareness of IFOF functional anatomy and integration between multimodal datasets coming from different sources has crucial implications for both neuroscientific knowledge and quality of neurosurgical treatments.

A Review of Cortical and Subcortical Stimulation Mapping for Language

Since the early descriptions of language function based on observations of patients with language deficits by Broca and Wernicke, neurosurgeons have been focused on characterizing the anatomic regions necessary for language perception and production, and preserving these structures during surgery to minimize patient deficits post operatively. In this supplementary issue on awake intraoperative mapping, we review language processing across multiple domains, highlighting key advances in direct electrical stimulation of different cortical and subcortical regions involved in naming, repetition, reading, writing, and syntax. We then discuss different intraoperative tasks for assessing the function of a given area and avoiding injury to critical, eloquent regions.

Neuropsychological management of the awake patient surgery: A protocol based on 3-year experience with glial tumors

INTRODUCTION

Glial brain tumours usually require neurosurgical treatment and they are associated with cognitive, emotional and behavioural impairments. Awake intraoperative brain mapping is the gold standard technique used to optimize the onco-functional balance. Neuropsychological assessment and intervention have relevance in this type of procedures. Currently, there is a lack of protocolled structure for the neuropsychological intervention being able to satisfy patient needs.

METHOD

A retrospective descriptive study of 52 patients was performed, all of them with a diagnosis of glial tumour. The structure of the protocol developed in our centre is reported, also data of neuropsychological evaluation, comparing baseline performance with both immediate posterior performance, and long term performance.

RESULTS

We describe our experience in each step of the intervention, highlighting the development of eight neurocognitive protocols for intraoperative brain mapping. The results of the neuropsychological examination objectify deficits in the immediate after surgery assessment which are reduced in the long-term assessment.

CONCLUSIONS

We emphasize the need of providing and structuring the cognitive and emotional aspects of patients suffering from any pathology that entails acquired brain damage in hospital environment. This type of approach is aimed at increasing the quality of life of cancer patients by structuring and optimizing tasks during their surgical intervention and attending to the neuropsychological difficulties they suffer.

The impact of emotional congruent and emotional neutral context on recognizing complex emotions in older adults

Adding context information has been shown to attenuate the age-related decline of emotion recognition. Specifically, older adults might benefit from emotional congruent context information due to their greater social knowledge. Contrary, emotional neutral context information might impair older adults' performance more due to their decline of inhibitory abilities. Our aim was to examine the age-related decline of complex emotion recognition across three context conditions (emotional congruent, emotional neutral and no context). We hypothesized that emotional congruent context will help older adults to perform at the same level as younger adults and expected worse performance of older adults in the emotional neutral and no context conditions. Twenty-eight older and 28 younger adults watched film clips with complex emotions preceded by a fixation cross (no context), emotional congruent context or emotional neutral context. Emotional neutral context affected older adults' performance more negatively than young adults', whereas emotional congruent improved performance of both young and older adults to a similar extent. Results suggest that emotional congruent context does not eliminate the overall age-related deficit in complex emotion recognition. In contrast, this deficit might be intensified by emotional neutral context.

The State of Resting State Networks

Functional MRI (fMRI) is currently used for pre-surgical planning, but is often limited to information on the motor and language systems. Resting state fMRI can provide more information on multiple other networks to the neurosurgeon and neuroradiologist; however, currently, these networks are not well known among clinicians. The purpose of this manuscript is to provide an introduction to these networks for the clinician and to discuss how they could be used in the future for precise and individualized surgical planning. We provide a short introduction to resting state fMRI and discuss multiple currently accepted resting state networks with a review of the literature. We review the characteristics and function of multiple somatosensory, association, and other networks. We discuss the concept of critical nodes in the brain and how the neurosurgeon can use this information to individually customize patient care. Although further research is necessary, future application of pre-surgical planning will require consideration of networks other than just motor and language in order to minimize post-surgical morbidity and customize patient care.

Mapping of Arithmetic Processing by Navigated Repetitive Transcranial Magnetic Stimulation in Patients with Parietal Brain Tumors and Correlation with Postoperative Outcome

BACKGROUND

Preserving functionality is important during neurosurgical resection of brain tumors. Specialized centers also map further brain functions apart from motor and language functions, such as arithmetic processing (AP). The mapping of AP by navigated repetitive transcranial magnetic stimulation (nrTMS) in healthy volunteers has been reported.

OBJECTIVE

The present study aimed to correlate the results of mapping AP with functional patient outcomes.

METHODS

We included 26 patients with parietal brain tumors. Because of preoperative impairment of AP, mapping was not possible in 8 patients (31%). We stimulated 52 cortical sites by nrTMS while patients performed a calculation task. Preoperatively and postoperatively, patients underwent a standardized number-processing and calculation test (NPCT). Tumor resection was blinded to nrTMS results, and the change in NPCT performance was correlated to resected AP-positive spots as identified by nrTMS.

RESULTS

The resection of AP-positive sites correlated with a worsening of the postoperative NPCT result in 12 cases. In 3 cases, no AP-positive sites were resected and the postoperative NPCT result was similar to or better than preoperatively. Also, in 3 cases, the postoperative NPCT result was better than preoperatively, although AP-positive sites were resected.

CONCLUSIONS

Despite presenting only a few cases, nrTMS might be a useful tool for preoperative mapping of AP. However, the reliability of the present results has to be evaluated in a larger series and by intraoperative mapping data.

Identifying clinical risk in low grade gliomas and appropriate treatment strategies, with special emphasis on the role of surgery

INTRODUCTION

Diffuse low-grade glioma (DLGG) is a chronic tumoral disease that ineluctably grows, migrates along white matter pathways, and progresses to a higher grade of malignancy. Areas covered: To determine the best individualized treatment attitude for each DLGG patient, and to redefine it over the years, i.e. to optimize the 'onco-functional balance' of serial and multimodal therapies, the understanding of the natural history of this chronic disease is crucial but not sufficient. A paradigmatic shift is to tailor the individual management according to the dynamic relationships between DLGG course and neural remodeling. In this spirit, a better knowledge of brain plasticity in a connectomal account of cerebral processing has enabled a dramatic improvement of both oncological and functional outcomes in DLGG patients, by increasing overall survival while preserving (or even improving) the quality of life. Expert commentary: Here, we propose an individualized and recursive therapeutic strategy in DLGG, leading to the concept of a 'personalized functional neuro-oncology', by emphasizing the role of early and maximal safe surgical resection(s) reliably achieved using intraoperative mapping of cortico-subcortical networks in awake patients.

A contemporary framework of language processing in the human brain in the context of preoperative and intraoperative language mapping

INTRODUCTION

The emergence of advanced in vivo neuroimaging methods has redefined the understanding of brain function with a shift from traditional localizationist models to more complex and widely distributed neural networks. In human language processing, the traditional localizationist models of Wernicke and Broca have fallen out of favor for a dual-stream processing system involving complex networks organized over vast areas of the dominant hemisphere. The current review explores the cortical function and white matter connections of human language processing, as well as their relevance to surgical planning.

METHODS

We performed a systematic review of the literature with narrative data analysis.

RESULTS

Although there is significant heterogeneity in the literature over the past century of exploration, modern evidence provides new insight into the true cortical function and white matter anatomy of human language. Intraoperative data and postoperative outcome studies confirm a widely distributed language network extending far beyond the traditional cortical areas of Wernicke and Broca.

CONCLUSIONS

The anatomic distribution of language networks, based on current theories, is explored to present a modern and clinically relevant interpretation of language function. Within this framework, we present current knowledge regarding the known effects of damage to both cortical and subcortical components of these language networks. Ideally, we hope this framework will provide a common language for which to base future clinical studies in human language function.

Cognitive eloquence in neurosurgery: Insight from graph theoretical analysis of complex brain networks

The structure and function of the brain can be described by complex network models, and the topological properties of these models can be quantified by graph theoretical analysis. This has given insight into brain regions, known as hubs, which are critical for integrative functioning and information transfer, both fundamental aspects of cognition. In this manuscript a hypothesis is put forward for the concept of cognitive eloquence in neurosurgery; that is regions (cortical, subcortical and white matter) of the brain which may not necessarily have readily identifiable neurological function, but if injured may result in disproportionate cognitive morbidity. To this end, the effects of neurosurgical resection on cognition is reviewed and an overview of the role of complex network analysis in the understanding of brain structure and function is provided. The literature describing network, behavioral, and cognitive effects resulting from lesions to, and disconnections of, centralized hub regions will be emphasized as evidence for the espousal of the concept of cognitive eloquence.

The Influence of Frontal Lobe Tumors and Surgical Treatment on Advanced Cognitive Functions

Brain cognitive functions affect patient quality of life. The frontal lobe plays a crucial role in advanced cognitive functions, including executive function, meta-cognition, decision-making, memory, emotion, and language. Therefore, frontal tumors can lead to serious cognitive impairments. Currently, neurosurgical treatment is the primary method to treat brain tumors; however, the effects of the surgical treatments are difficult to predict or control. The treatment may both resolve the effects of the tumor to improve cognitive function or cause permanent disabilities resulting from damage to healthy functional brain tissue. Previous studies have focused on the influence of frontal lesions and surgical treatments on patient cognitive function. Here, we review cognitive impairment caused by frontal lobe brain tumors.

Stimulation mapping of white matter tracts to study brain functional connectivity

Despite advances in the new science of connectomics, which aims to comprehensively map neural connections at both structural and functional levels, techniques to directly study the function of white matter tracts in vivo in humans have proved elusive. Direct electrical stimulation (DES) mapping of the subcortical fibres offers a unique opportunity to investigate the functional connectivity of the brain. This original method permits real-time anatomo-functional correlations, especially with regard to neural pathways, in awake patients undergoing brain surgery. In this article, the goal is to review new insights, gained from axonal DES, into the functional connectivity underlying the sensorimotor, visuospatial, language and sociocognitive systems. Interactions between these neural networks and multimodal systems, such as working memory, attention, executive functions and consciousness, can also be investigated by axonal stimulation. In this networking model of conation and cognition, brain processing is not conceived as the sum of several subfunctions, but results from the integration and potentiation of parallel-though partially overlapping-subnetworks. This hodotopical account, supported by axonal DES, improves our understanding of neuroplasticity and its limitations. The clinical implications of this paradigmatic shift from localizationism to hodotopy, in the context of brain surgery, neurology, neurorehabilitation and psychiatry, are discussed.

White-matter development is different in bilingual and monolingual children: a longitudinal DTI study

Although numerous people grow up speaking more than one language, the impact of bilingualism on brain developing neuroanatomy is still poorly understood. This study aimed to determine whether the changes in the mean fractional-anisotropy (MFA) of language pathways are different between bilingual and monolingual children. Simultaneous-bilinguals, sequential-bilinguals and monolingual, male and female 10–13 years old children participated in this longitudinal study over a period of two years. We used diffusion tensor tractography to obtain mean fractional-anisotropy values of four language related pathways and one control bundle: 1-left-inferior-occipitofrontal fasciculus/lIFOF, 2-left-arcuate fasciculus/lAF/lSLF, 3-bundle arising from the anterior part of corpus-callosum and projecting to orbital lobe/AC-OL, 4-fibres emerging from anterior-midbody of corpus-callosum (CC) to motor cortices/AMB-PMC, 5- right-inferior-occipitofrontal fasciculus rIFOF as the control pathway unrelated to language. These values and their rate of change were compared between 3 groups. FA-values did not change significantly over two years for lAF/lSLF and AC-OL. Sequential-bilinguals had the highest degree of change in the MFA value of lIFOF, and AMB-PMC did not present significant group differences. The comparison of MFA of lIFOF yielded a significantly higher FA-value in simultaneous bilinguals compared to monolinguals. These findings acknowledge the existing difference of the development of the semantic processing specific pathway between children with different semantic processing procedure. These also support the hypothesis that age of second language acquisition affects the maturation and myelination of some language specific white-matter pathways.

Sexuality after surgery for diffuse low-grade glioma

BACKGROUND

Although neurological and neurocognitive outcomes have previously been studied after resection of diffuse low-grade glioma (DLGG), the impact of surgery on sexual life has not been investigated. Our aim was to assess whether DLGG surgery could have consequences on sexual experience.

METHODS

Anonymous standardized questionnaires concerning sexual functioning, including the Arizona Sexual Experiences Scale (ASEX) and a subjective statement, were completed by 32 patients who underwent surgery for DLGG. All patients returned to a normal social and professional life following resection, with neither neurological deficits nor depression. No radiotherapy was administered, and patients who received chemotherapy were without treatment for at least 1 year.

RESULTS

Seventeen patients (53%) reported a postoperative sexual change, with subjective deterioration in 15 (88%) and improvement in 2 (12%). Sexual dysfunction according to ASEX affected 9 of 15 women (60%) and 5 of 17 men (29%). Right-sided resections were associated with more difficulties in reaching orgasm than left-sided resections (P < .02). Men with temporal lobe resection displayed more reduction in sexual drive (P < .003) and sexual arousal (P < .004) than women, resulting in significant higher overall ASEX scores for temporal lobe resections in men (P = .01). Men remaining on antiepileptic drugs who underwent right-sided resection displayed higher overall ASEX scores than women (P = .031).

CONCLUSIONS

This first evaluation of sexual life after surgery for DLGG suggests that sexual dysfunction is common in this population. Therefore, we suggest that sexual health should consistently be addressed during routine pre- and postoperative examination of patients with DLGG.

Broca's area damage is necessary but not sufficient to induce after-effects of cathodal tDCS on the unaffected hemisphere in post-stroke aphasia

BACKGROUND

The inter-individual variability of behavioral effects after tDCS applied to the unaffected right hemisphere in stroke may be related to factors such as the lesion location.

OBJECTIVE/HYPOTHESIS

We investigated the effect of left Broca's area (BA) damage on picture naming in aphasic patients after cathodal tDCS applied over the right BA.

METHODS

We conducted a study using pre-interventional diffusion and resting state functional MRI (rsfMRI) and two cross-over tDCS sessions (TYPE: sham and cathodal) over the right homologous BA in aphasic stroke patients with ischemic lesions involving the left BA (BA+) or other left brain areas (BA-). Picture naming accuracy was assessed after each session. Inter-hemispheric (IH) functional balance was investigated via rsfMRI connectivity maps using the right BA as a seed. Probabilistic tractography was used to study the integrity of language white matter pathways.

RESULTS

tDCS had different effects on picture naming accuracy in BA+ and BA- patients (TYPE × GROUP interaction, F(1,19): 4.6, P: 0.04). All BA- patients except one did not respond to tDCS and demonstrated normal IH balance between the right and left BA when compared to healthy subjects. BA+ patients were improved by tDCS in 36% and had decreased level of functional IH balance. Improvement in picture naming after cathodal tDCS was associated with the integrity of the arcuate fasciculus in BA+ patients.

CONCLUSIONS

Behavioral effects of cathodal tDCS on the unaffected right hemisphere differ depending on whether BA and the arcuate fasciculus are damaged. Therefore, IH imbalance could be a direct consequence of anatomical lesions.

A re-examination of neural basis of language processing: proposal of a dynamic hodotopical model from data provided by brain stimulation mapping during picture naming

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.

A case of bilateral frontal tumors without "frontal syndrome"

We report the longitudinal case study of a right-handed patient harboring two frontal tumors that benefited from bilateral simultaneous surgery. The tumors were WHO Grade II gliomas located in the left inferior frontal area (including the cingulate gyrus) and the right anterior superior frontal gyrus. The double tumor resection was guided by direct electrical stimulation of brain areas while the patient was awake. Neuropsychological assessments were administered before and after the surgery to analyse how the brain functions in the presence of two frontal gliomas that affect both hemispheres and reacts to a bilateral resection, which can brutally compromise the neuronal connectivity, progressively established during the infiltrating process. We showed that both the tumor infiltration and their bilateral resection did not lead to a "frontal syndrome" or a "dysexecutive syndrome" predicted by the localization models. However, a subtle fragility was observed in fine-grain language, memory and emotional skills. This case study reveals the significance of brain plasticity in the reorganization of cognitive networks, even in cases of bilateral tumors. It also confirms the clinical relevance of hodotopical brain models, which considers the brain to be organized in parallel-distributed networks around cortical centers and epicenters.

Selection of intraoperative tasks for awake mapping based on relationships between tumor location and functional networks

Intraoperative electrical brain mapping is currently the most reliable method to identify eloquent cortical and subcortical structures at the individual level and to optimize the extent of resection of intrinsic brain tumors. The technique allows the preservation of quality of life, not only allowing avoidance of severe neurological deficits but also facilitating preservation of high neurocognitive functions. To accomplish this goal, however, it is crucial to optimize the selection of appropriate intraoperative tasks, given the limited intrasurgical awake time frame. In this review, the authors' aim was to propose specific parameters that could be used to build a personalized protocol for each patient. They have focused on lesion location and relationships with functional networks to guide selection of intrasurgical tasks in an effort to increase reproducibility among neurooncological centers.

Strengths and weaknesses of multimodal processing in a group of adults with gliomas

The present study aimed to analyze the multimodal skills that would be spared, altered, or impaired by gliomas that slowly infiltrate various and diversely localized areas in the cerebral hemispheres. Ten patients and 60 healthy controls were evaluated using four multimodal processing paradigms across 11 tasks. Our objectives were as follows: (a) to describe the strengths and weaknesses of the glioma patients' multimodal processing performance after accounting for task specificity and their individual performances compared to those of the control group; (b) to determine the correlation between lesion localization and impairments; and (c) to identify the tasks that were most sensitive to tumor infiltration and plasticity limits. Our results show that patients as a whole were efficient at most tasks; however, the patients exhibited difficulties in the productive picture-naming task, the receptive verbal judgment task, and the visual/graphic portion of the dual-attention task. The individual case reports show that the difficulties were distributed across the patients and did not correlate with lesion localization and tumor type.

Association fibers connecting the Broca center and the lateral superior frontal gyrus: a microsurgical and tractographic anatomy

Object

Recently, intraoperative mapping has disclosed that, in addition to the classic language centers (that is, the Broca and Wernicke centers), other cortical regions may also play an important role in language organization. In the prefrontal cortex, although the lateral superior frontal gyrus (LSFG) could have language-related functions, there are no detailed reports that demonstrate the anatomical connection between the LSFG and other well-known language cortices, such as the Broca center. To show the existence of the structural connection, white matter association fibers between the inferior frontal gyrus (IFG) and the LSFG were examined using fiber dissection (FD) and diffusion tensor (DT) imaging–based tractography.

Methods

Eight cadaveric cerebral hemispheres were dissected to reveal the association fibers between the IFG and LSFG. The DT imaging–based tractography studies targeting the prefrontal cortex were obtained in 53 right-handed patients who had no organic cerebral lesions.

Results

The association fiber tract between Brodmann area 44/45 (the Broca center in the dominant hemisphere) and LSFG were detected in all specimens by FD. In the DT imaging–based tractography studies, the tract was identified in all patients bilaterally, except for the 4 in whom the tract was detected only in the left hemisphere. This tract was spread significantly wider in the left than in the right hemisphere, and left lateralization was evident in male patients.

Conclusions

Based on its character, this tract was named the Broca-LSFG pathway. These findings suggest a close relationship between this pathway and language organization. The structural anatomy of the Broca-LSFG pathway may explain speech disturbances induced by LSFG stimulation that are sometimes observed during intraoperative language mapping.

A new concept of diffuse (low-grade) glioma surgery

Preservation and even improvement of the quality of life is currently a priority in surgery for gliomas, in addition to the optimization of the extent of resection with significant increase of the overall survival. In this setting, the goal of the present review is to revisit technical aspects of glioma surgery in the lights of new concepts both in the fields of neurooncology and cognitive neurosciences, which recently emerged from translational researches - with special emphasis on diffuse low grade gliomas.Firstly, the vascularisation (arteries and veins) has to be more systematically spared, by performing subpial dissection and by limiting the use of coagulation within the brain. Secondly, individual cortical as well as subcortical mapping must be more regularly considered, with the aim of better understanding and preserving the white matter pathways underlying the functional connectivity - even in presumed "non-eloquent areas", to perform "supra-complete" resection.Therefore, brain surgeons should change their state of mind, in order to operate the nervous system involved by a chronic tumoral disease (and no more by operating a tumor mass within the brain). In other words, the neurosurgeon should see first the brain, and not the glioma, to adapt his surgical procedure to the three-dimensional anatomo-functional organization of each patient. It implies that brain surgeon must change his technique within the central nervous system, which has to be different from the surgical technique outside the brain. This perspective seems to represent the best way to build a modern and personalized "functional surgical neurooncology".

Frontal terminations for the inferior fronto-occipital fascicle: anatomical dissection, DTI study and functional considerations on a multi-component bundle

The anatomy and functional role of the inferior fronto-occipital fascicle (IFOF) remain poorly known. We accurately analyze its course and the anatomical distribution of its frontal terminations. We propose a classification of the IFOF in different subcomponents. Ten hemispheres (5 left, 5 right) were dissected with Klingler's technique. In addition to the IFOF dissection, we performed a 4-T diffusion tensor imaging study on a single healthy subject. We identified two layers of IFOF. The first one is superficial and antero-superiorly directed, terminating in the inferior frontal gyrus. The second is deeper and consists of three portions: posterior, middle and anterior. The posterior component terminates in the middle frontal gyrus (MFG) and dorso-lateral prefrontal cortex. The middle component terminates in the MFG and lateral orbito-frontal cortex. The anterior one is directed to the orbito-frontal cortex and frontal pole. In vivo tractography study confirmed these anatomical findings. We suggest that the distribution of IFOF fibers within the frontal lobe corresponds to a fine functional segmentation. IFOF can be considered as a "multi-function" bundle, with each anatomical subcomponent subserving different brain processing. The superficial layer and the posterior component of the deep layer, which connects the occipital extrastriate, temporo-basal and inferior frontal cortices, might subserve semantic processing. The middle component of the deep layer could play a role in a multimodal sensory-motor integration. Finally, the anterior component of the deep layer might be involved in emotional and behavioral aspects.

Double dissociation between syntactic gender and picture naming processing: a brain stimulation mapping study

Neural foundations of syntactic gender processing remain poorly understood. We used electrostimulation mapping in nine right-handed awake patients during surgery for a glioma within the left hemisphere, to study whether the cortico-subcortical structures involved in naming versus syntactic gender processing are common or distinct. In French, the article determines the grammatical gender. Thus, the patient was asked to perform a picture naming task and to give the appropriate article for each picture, with and without stimulation. Cortical stimulation elicited reproducible syntactic gender disturbances in six patients, in the inferior frontal gyrus (three cases), and in the posterior middle temporal gyrus (three cases). Interestingly, no naming disorders were generated during stimulation of the syntactic sites, while cortical areas inducing naming disturbances never elicited grammatical gender errors when stimulated. Moreover, at the subcortical level, stimulation of the white matter lateral to the caudate nucleus induced gender errors in three patients, with no naming disorders. Using cortico-subcortical electrical mapping in awake patients, we demonstrate for the first time (1) a double dissociation between syntactic gender and naming processing, supporting independent network model rather than serial theory, (2) the involvement of the left inferior frontal gyrus, especially the pars triangularis, and the posterior left middle temporal gyrus in grammatical gender processing, (3) the existence of white matter pathways, likely a sub-part of the left superior longitudinal fasciculus, underlying a large-scale distributed cortico-subcortical circuit which might selectively sub-serve syntactic gender processing, even if interconnected with parallel sub-networks involved in naming (semantic and phonological) processing.

Brain Hodotopy: From Esoteric Concept to Practical Surgical Applications

BACKGROUND:

The traditional neurosurgical approach to cerebral lesions is based on the classic view of a rigid brain organization in fixed “eloquent” areas. However, this method is brought into discussion by the conceptual and methodological advances in neurosciences that provide a more dynamic representation of the anatomo-functional distribution of the human central nervous system (CNS).

OBJECTIVE AND METHODS:

We review the relevant literature concerning the main features of the modern CNS representation and their implications in neurosurgical practice.

RESULTS:

The CNS is an integrated, wide, plastic network made up of cortical functional epicenters, “topic organization,” connected by both short-local and large-scale white matter fibers, ie, “hodological organization.” According to this model, called hodotopic, brain function results from parallel streams of information dynamically modulated within an interactive, multimodal, and widely distributed circuit. The application of this framework, which can be studied by combining preoperative, intraoperative, and postoperative mapping techniques, enables the neurosurgeon exploration of the individual anatomo-functional architecture, including neurocognitive and emotional aspects. Thus, it is possible to adapt the surgical approach specifically to each patient and to each lesion according to the individual organization. Several experiences demonstrate the possibility of removing regions traditionally considered inoperable without inducing permanent deficits and the potential use of these areas as a safe passage to deeper territories.

CONCLUSION:

We advocate the more systematic integration of a hodotopical view of the CNS to improve the surgical indications and planning for brain lesions, with the goal of optimizing both the extent of resection and functional outcome.

A method to map the visual cortex during an awake craniotomy

Much has been reported regarding the technique of performing an awake craniotomy with cortical mapping for the functional cortex responsible for sensorimotor activity and language. However, documentation for mapping the visual cortex during an awake craniotomy with a description of its technical details is rare. The authors report the case of a patient who underwent an awake craniotomy with mapping of the visual cortex to remove a glioma situated in the left medial occipital lobe. The techniques that made such a mapping procedure possible are discussed.

Awake surgery for nonlanguage mapping

OBJECTIVE

During the past decade, numerous reports have supported the contribution of awake mapping in surgical removal of brain lesions in eloquent areas, with a significant increase of the extent of resection while minimizing the risk of permanent deficit--and even improving quality of life.

METHODS

Most of these awake procedures were performed in patients with lesions in language areas, to avoid postoperative aphasia. Surprisingly, mapping of nonlanguage functions received less attention, despite the possible consequences of deficits other than aphasia on daily life. Visuospatial and cognitive deficits are reported after brain surgery, because of more objective and extensive neuropsychological assessments.

RESULTS AND CONCLUSION

This review provides new insights into the indications of awake craniotomies for nonlanguage mapping in surgery for lesions in areas not related to language processing.

Brain mapping in neuro-oncology: what is the future?

Surgery is the first treatment in neuro-oncology. However, brain gliomas are frequently located within eloquent areas. Therefore, in order to maximize the extent of resection while preserving cerebral functions, owing to major interindividual anatomo–functional variability across patients, functional mapping is now mandatory. Preoperative functional neuroimaging allows a better understanding of the individual organization of brain networks, leading to optimized surgical indications and planning. Intrasurgical cortical and subcortical stimulation, often carried out in awake patients, enables assessment of the performance of online anatomo–functional correlations, with increased resection according to functional boundaries. Postoperative functional neuroimaging following recovery, regularly carried out after active rehabilitation, provides information regarding cerebral plasticity over time, possibly opening the door to another surgery(ies). In summary, brain mapping allows surgical removal in eloquent areas classically considered as ‘inoperable’, and also preservation or even improvement of quality of life, while increasing median survival. The future persepctive is now to move towards dynamic therapeutic strategy based on a multiple-stage surgical approach, combined with (neo)adjuvant chemotherapy and/or radiotherapy. In addition, cerebral mapping enables a better knowledge of brain processing, especially concerning connectivity and plasticity, creating a link between neuro-oncology and cognitive neurosciences, and opening the concept of ‘functional neuro-oncology’.

Speaking without Broca's area after tumor resection

We present the case of a right-handed patient who received surgical treatment for a left frontal WHO grade II glioma invading the left inferior and middle frontal gyri, the head of the caudate nucleus, the anterior limb of the internal capsule and the anterior insula, in direct contact also with the anterior-superior part of the lentiform nucleus. The tumor resection was guided by direct electrical stimulation on brain areas, while the patient was awake. Adding a narrative production task to the neuropsychological assessment, we compared pre-, peri- and post-surgical language skills in order to analyze the effects of the tumor infiltration and the consequences of the left IFG resection, an area known to be involved in various language and cognitive processes. We showed that the tumor infiltration and its resection did not lead to the severe impairments predicted by the localization models assigning a significant role in language processing to the left frontal lobe, notably Broca's area. We showed that slow tumor evolution - the patient had been symptom-free for a long time - enabled compensatory mechanisms to process most language functions endangered by the tumor infiltration. However, a subtle fragility was observed in two language devices, i.e., reported speech and relative clauses, related to minor working memory deficits. This case study of a patient speaking without Broca's area illustrates the efficiency of brain plasticity, and shows the necessity to broaden pre-, peri-, post-surgery language and cognitive assessments.