Multimodality word-finding distinctions in cortical stimulation mapping

A left-lateralized dorsolateral prefrontal network for naming

The ability to connect the form and meaning of a concept, known as word retrieval, is fundamental to human communication. While various input modalities could lead to identical word retrieval, the exact neural dynamics supporting this convergence relevant to daily auditory discourse remain poorly understood. Here, we leveraged neurosurgical electrocorticographic (ECoG) recordings from 48 patients and dissociated two key language networks that highly overlap in time and space integral to word retrieval. Using unsupervised temporal clustering techniques, we found a semantic processing network located in the middle and inferior frontal gyri. This network was distinct from an articulatory planning network in the inferior frontal and precentral gyri, which was agnostic to input modalities. Functionally, we confirmed that the semantic processing network encodes word surprisal during sentence perception. Our findings characterize how humans integrate ongoing auditory semantic information over time, a critical linguistic function from passive comprehension to daily discourse.

The Greek linguistic assessment for awake brain surgery: development process and normative data

Language mapping with direct electrical stimulation is considered the gold standard in surgical treatment of brain tumors. Assessing a variety of language functions intraoperatively can affect the extent of the tumor resection as well as the patient's postoperative quality of life. Although most tests include preoperative sessions where tasks are personalised to each patient, normative data are essential since they can ensure that the presented stimuli can be responded appropriately. In this study, we describe the development and standardisation procedures of the first linguistic test in Greek, designed specifically for brain mapping during awake craniotomies. The tasks are developed to comply with the special conditions and restrictions of language assessment inside the operating room. Each task is controlled for various psycholinguistic and lexical variables and it is associated with specific neuroanatomical areas and linguistic processes. Our population consists of 80 right-handed, healthy, Greek-speaking individuals aged 20-60 years. We found only a few main effects and interactions of demographic variables on our test scores. Most differences were found between age groups, since older participants tend to perform slightly worse than younger ones. Therefore, percentiles and cut-off scores were calculated separately for each demographic group. Regarding the clinical application of GLAABS, we describe the procedures we followed to administer it to brain tumor patients from our department and also discuss how sensitivity and specificity can affect patients' postoperative course.

The Use of Standardized Intraoperative Language Tests in Awake Craniotomies: A Scoping Review

Assessment of speech and language functions is an essential part of awake craniotomies. Although standardized and validated tests have several advantages compared to homemade (or mixed) batteries, in the literature it is unclear how such tests are used or whether they are used at all. In this study, we performed a scoping review in order to locate standardized and validated intraoperative language tests. Our inquiry included two databases (PubMED and MEDLINE), gray literature, and snowball referencing. We discovered 87 studies reporting use of mixed batteries, which consist of homemade tasks and tests borrowed from other settings. The tests we found to meet the validation and standardization criteria we set were ultimately three (n = 3) and each one has its own advantages and disadvantages. We argue that tests with high sensitivity and specificity not only can lead to better outcomes postoperatively, but they can also help us to gain a better understanding of the neuroanatomy of language.

History of awake mapping and speech and language localization: from modules to networks

Lesion-symptom correlations shaped the early understanding of cortical localization. The classic Broca-Wernicke model of cortical speech and language organization underwent a paradigm shift in large part due to advances in brain mapping techniques. This initially started by demonstrating that the cortex was excitable. Later, advancements in neuroanesthesia led to awake surgery for epilepsy focus and tumor resection, providing neurosurgeons with a means of studying cortical and subcortical pathways to understand neural architecture and obtain maximal resection while avoiding so-called critical structures. The aim of this historical review is to highlight the essential role of direct electrical stimulation and cortical-subcortical mapping and the advancements it has made to our understanding of speech and language cortical organization. Specifically, using cortical and subcortical mapping, neurosurgeons shifted from a localist view in which the brain is composed of rigid functional modules to one of dynamic and integrative large-scale networks consisting of interconnected cortical subregions.

Cortical stimulation mapping for localization of visual and auditory language in pediatric epilepsy patients

OBJECTIVE

To determine resection margins near eloquent tissue, electrical cortical stimulation (ECS) mapping is often used with visual naming tasks. In recent years, auditory naming tasks have been found to provide a more comprehensive map. Differences in modality-specific language sites have been found in adult patients, but there is a paucity of research on ECS language studies in pediatric patients. The goals of this study were to evaluate word-finding distinctions between visual and auditory modalities and identify which cortical subregions most often contain critical language function in a pediatric population.

METHODS

Twenty-one pediatric patients with epilepsy or temporal lobe pathology underwent ECS mapping using visual (n = 21) and auditory (n = 14) tasks. Fisher's exact test was used to determine whether the frequency of errors in the stimulated trials was greater than the patient's baseline error rate for each tested modality and subregion.

RESULTS

While the medial superior temporal gyrus was a common language site for both visual and auditory language (43.8% and 46.2% of patients, respectively), other subregions showed significant differences between modalities, and there was significant variability between patients. Visual language was more likely to be located in the anterior temporal lobe than was auditory language. The pediatric patients exhibited fewer parietal language sites and a larger range of sites overall than did adult patients in previously published studies.

CONCLUSIONS

There was no single area critical for language in more than 50% of patients tested in either modality for which more than 1 patient was tested (n > 1), affirming that language function is plastic in the setting of dominant-hemisphere pathology. The high rates of language function throughout the left frontal, temporal, and anterior parietal regions with few areas of overlap between modalities suggest that ECS mapping with both visual and auditory testing is necessary to obtain a comprehensive language map prior to epileptic focus or tumor resection.

Cortical Language Areas and Plasticity in Pediatric Patients With Epilepsy: A Review

Chronic injury to the brain from seizure activity is associated with decreased language skills in pediatric patients, as measured on neuropsychological tests for language function and academic achievement. This makes the study of language in patients with epilepsy clinically necessary. Functional magnetic resonance imaging and direct electrical cortical stimulation have been used to evaluate aspects of cortical language processing in healthy adults and in adults with epilepsy or other neurological insults. Results of these studies help to locate cortical language areas that are involved with modality-specific language processing (visual naming, auditory naming, sentence-completion, and repetition) and the neuroplasticity of language areas in the setting of neurological injury and reorganization. A better understanding of language processing contributes to a more efficient and efficacious electrical cortical stimulation mapping of language areas for patients with intractable epilepsy who are undergoing preresection evaluation. Most of the current literature on localization and reorganization of cortical language areas in the setting of epilepsy concerns the adult patient population, whereas the literature on pediatric patients is substantially lacking in comparison. This article reviews the conclusions drawn thus far from Wada, magnetoencephalography, functional magnetic resonance imaging, and electrical cortical stimulation language studies on types of language reorganization seen in pediatric patients with intractable temporal lobe epilepsy and the clinical factors associated with reorganization, and proposes future directions of research to further the academic and clinical understanding of language processing in pediatric patients.

Test-retest reliability of cortical language mapping in a patient with refractory focal epilepsy: 11 years later

Electrical stimulation mapping (ESM) is considered the gold standard for identification of essential language cortex and is especially important in patients for whom classic language landmarks are less useful because of reorganization in response to epileptogenic or neoplastic cortex. However, little is known regarding the reliability of the procedure, particularly over extended time intervals. The authors present the case of a young man with refractory left temporal lobe epilepsy in the setting of a low-grade left temporal tumor who had undergone intraoperative language mapping at age 14 years and repeat mapping at age 25. Results from both the initial ESM and the repeat ESM 11 years later revealed a positive auditory description naming site in the same location on the superior temporal gyrus, at the anterior aspect of the tumor. This case provides support for the reliability of ESM and underscores intraindividual reliability in the location of language cortex over a prolonged period.

Object naming in epilepsy and epilepsy surgery

The ability to express oneself verbally is critical for success in academic, occupational, and social domains. Unfortunately, word-finding or "naming" difficulty is the most common cognitive complaint among individuals with temporal lobe epilepsy (TLE), and a substantial body of work over the past several decades has documented naming impairment in left (language-dominant) TLE, with further risk to naming ability following left temporal lobe resection for seizure control. With these findings well established, this paper reviews more recent work that has aimed to identify the neuroanatomical substrates of naming, understand how adverse structural and functional effects of TLE might impinge upon these brain regions, predict and potentially reduce the risk of postoperative naming decline, and begin to understand naming difficulty in TLE from a developmental perspective. Factors that have confounded interpretation and hindrances to progress are discussed, and suggestions are provided for improved empirical investigation and directions for future research.