Surgical treatment for epilepsy involving language cortices: A combined process of electrical cortical stimulation mapping and intra-operative continuous language assessment

Functional mapping of language-related areas from natural, narrative speech during awake craniotomy surgery

Accurate localization of brain regions responsible for language and cognitive functions in epilepsy patients is important. Electrocorticography (ECoG)-based real-time functional mapping (RTFM) has been shown to be a safer alternative to electrical cortical stimulation mapping (ESM), which is currently the clinical/gold standard. Conventional methods for analyzing RTFM data mostly account for the ECoG signal in certain frequency bands, especially high gamma. Compared to ESM, they have limited accuracy when assessing channel responses. In the present study, we developed a novel RTFM method based on tensor component analysis (TCA) to address the limitations of current estimation methods. Our approach analyzes the whole frequency spectrum of the ECoG signal during natural continuous speech. We construct third-order tensors that contain multichannel time-frequency information and use TCA to extract low-dimensional temporal, spectral and spatial modes. Temporal modulation scores (correlation values) are then calculated between the time series of voice envelope features and TCA-estimated temporal courses, and significant temporal modulation determines which components' channel weightings are displayed to the neurosurgeon as a guide for follow-up ESM. In our experiments, data from thirteen patients with refractory epilepsy were recorded during preoperative evaluation for their epileptogenic zones (EZs), which were located adjacent to the eloquent cortex. Our results showed higher detection accuracy of our proposed method in a narrative speech task, suggesting that our method complements ESM and is an improvement over the prior RTFM method. To our knowledge, this is the first TCA-based method to pinpoint language-specific brain regions during continuous speech that uses whole-band ECoG.

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.

Clinical application of intraoperative trial-free online-based language mapping for patients with refractory epilepsy

OBJECTIVE

The objective of the study was to develop and clinically test a trial-free online-based language mapping method for localizing the eloquent cortex easily in epilepsy operation.

METHODS

Nine patients with refractory epilepsy were included in this study according to the results of preoperative evaluation for their epileptogenic zones (EZs) located adjacent to the eloquent cortex. When patients were awakened up from general anesthesia during operation, the trial-free online-based language-mapping paradigm was performed. All positive points marked on the cortex in each test were labeled and superimposed together as the result of functional mapping for each patient. The eloquent cortex was mapped according to the results obtained both from the intraoperative trial-free task localization method and the traditional electrical cortical stimulation (ECS).

RESULTS

All patients completed this paradigms twice within 10 min. Based on the results of mapping, the EZs were tried to fully resected on the premise of preserving the mapped eloquent cortex as much as possible. The postoperative follow-up showed the outcome of Engel I in six patients and Engel II in three patients, whereas only two patients had aphemia after surgery and recovered within one week and three months, respectively.

SIGNIFICANCE

The intraoperative trial-free online-based language mapping method was primarily identified to be safe and effective. This novel method seems to be promising and worthy of improvement.

Multitask preoperative language mapping in epilepsy surgery: A combination of navigated transcranial magnetic stimulation and extra-operative electrical cortical stimulation

Navigated transcranial magnetic stimulation (nTMS) is increasingly applied in language mapping. However, the application mode and task selection of nTMS are not standardized. The aim of this study was to assessed the necessity and validity of multitask nTMS language mapping by comparing results with extraoperative electrical cortical stimulation (eoECS). In this study, sixteen epilepsy surgery patients were examined by nTMS and eoECS language mapping, and the two results were compared. The mapping results were validated with pre- to postoperative language assessments. Compared with eoECS, nTMS showed the overall sensitivity of 82.4%, specificity of 95.1%, positive predictive value of 66.7%, and negative predictive value of 97.8%. Spontaneous speech was the most sensitive task in the frontal area, naming was the sensitive task in both frontal and temporal areas. The false responses were mainly located in the perisylvian region. Multitask nTMS helps to reduce missing language relevant cortex preoperatively. Selecting spontaneous speech and naming tasks in frontal area, comprehension and naming tasks in temporal and posterior language area would strike the balance between the validity and efficiency of the mapping procedure. These results manifested the necessity of applying multitask in nTMS language mapping. Our study highlighted the importance of the nTMS evaluation mode and task selection for epilepsy patients.

Challenges of Epilepsy Surgery

Though frequently effective in the management of medically refractory seizures, epilepsy surgery presents numerous challenges. Selection of the appropriate candidate patients who are likely to benefit from surgery is critical to achieving seizure freedom and avoiding neurocognitive morbidity. Identifying the seizure focus and mapping epileptogenic networks involves an interdisciplinary team dedicated to formulating a safe and effective surgical plan. Various strategies can be employed either to eliminate the epileptic focus or to modulate network activity, including resection of the focus with open surgery or laser interstitial thermal therapy; modulation of epileptogenic firing patterns with responsive neurostimulation, deep brain stimulation, or vagus nerve stimulation; or non-invasive disconnection of epileptic circuits with focused ultrasound, which is also discussed in greater detail in the subsequent chapter in our series. We review several challenges of epilepsy surgery that must be thoughtfully addressed in order to ensure its success.

Effects of Epilepsy on Language Functions: Scoping Review and Data Mining Findings

PURPOSE

This study involved a scoping review to identify possible gaps in the empirical description of language functioning in epilepsy in adults. With access to social network data, data mining was used to determine if individuals with epilepsy are expressing language-related concerns.

METHOD

For the scoping review, scientific databases were explored to identify pertinent articles. Findings regarding the nature of epilepsy etiologies, patient characteristics, tested language modalities, and language measures were compiled. Data mining focused on social network databases to obtain a set of relevant language-related posts.

RESULTS

The search yielded 66 articles. Epilepsy etiologies except temporal lobe epilepsy and older adults were underrepresented. Most studies utilized aphasia tests and primarily assessed single-word productions; few studies included healthy control groups. Data mining revealed several posts regarding epilepsy-related language problems, including word retrieval, reading, writing, verbal memory difficulties, and negative effects of epilepsy treatment on language.

CONCLUSION

Our findings underscore the need for future specification of the integrity of language in epilepsy, particularly with respect to discourse and high-level language abilities. Increased awareness of epilepsy-related language issues and understanding the patients' perspectives about their language concerns will allow researchers and speech-language pathologists to utilize appropriate assessments and improve quality of care.

Invasive epilepsy surgery evaluation

Intracranial EEG (iEEG) recordings are widely used for the work up of pharmacoresistant epilepsy. Different iEEG recording techniques namely subdural grids, strips, depth electrodes and stereoencephalography (SEEG) are available with distinct limitations and advantages. Epilepsy centres mastering multiple techniques apply them in an individualised patient approach. These tools are used to map the seizure onset zone which is pivotal in approximating the epileptogenic zone, i.e. the zone which is indispensable for the generation of seizures and when resected will render the patient seizure free. Besides, the implanted electrodes can be used to define eloquent cortex through direct cortical stimulation. Different clinical scenarios exist which favour one iEEG recording technique over the other. Proximity of the presumed epileptogenic zone to eloquent cortex, for example, is a clinical scenario which may favour grid electrodes over SEEG. We here review the indication for iEEG for the work-up of patients suffering from pharmacoresistant epilepsy. In addition, we provide a description of the recording techniques focussing on the main techniques used: grid electrodes, depth electrodes and stereoencephalography. We then outline different clinical scenarios and the preferred technical approach for intracranial recordings in these scenarios. Finally, we highlight which advances have been made in the field of iEEG and which advances are in the pipeline waiting to be established for clinical use. This review provides the clinician with an update on the diagnostic use of intracranial EEG for epilepsy surgery and thus aids in understanding patient selection for this technique which may ultimately improve referral patterns.

What do patients with epilepsy tell us about language dynamics? A review of fMRI studies

The objective of this review is to resume major neuroimaging findings on language organization and plasticity in patients with focal and refractory epilepsy, to discuss the effect of modulatory variables that should be considered alongside patterns of reorganization, and to propose possible models of language reorganization. The focal and refractory epilepsy provides a real opportunity to investigate various types of language reorganization in different conditions. The 'chronic' condition (induced by the epileptogenic zone or EZ) is associated with either recruitment of homologous regions of the opposite hemisphere or recruitment of intrahemispheric, nonlinguistic regions. In the 'acute' condition (neurosurgery and EZ resection), the initial interhemispheric shift (induced by the chronic EZ) could follow a reverse direction, back to the initial hemisphere. These different patterns depend on several modulatory factors and are associated with various levels of language performance. As a neuroimaging tool, functional magnetic resonance imaging enables the detailed investigation of both hemispheres simultaneously and allows for comparison with healthy controls, potentially creating a more comprehensive and more realistic picture of brain-language relations. Importantly, functional neuroimaging approaches demonstrate a good degree of concordance on a theoretical level, but also a considerable degree of individual variability, attesting to the clinical importance with these methods to establish, empirically, language localization in individual patients. Overall, the unique features of epilepsy, combined with ongoing advances in technology, promise further improvement in understanding of language substrate.

In vivo bioluminescence imaging for prolonged survival of transplanted human neural stem cells using 3D biocompatible scaffold in corticectomized rat model

Stem cell-based treatment of traumatic brain injury has been limited in its capacity to bring about complete functional recovery, because of the poor survival rate of the implanted stem cells. It is known that biocompatible biomaterials play a critical role in enhancing survival and proliferation of transplanted stem cells via provision of mechanical support. In this study, we noninvasively monitored in vivo behavior of implanted neural stem cells embedded within poly-l-lactic acid (PLLA) scaffold, and showed that they survived over prolonged periods in corticectomized rat model. Corticectomized rat models were established by motor-cortex ablation of the rat. F3 cells expressing enhanced firefly luciferase (F3-effLuc) were established through retroviral infection. The F3-effLuc within PLLA was monitored using IVIS-100 imaging system 7 days after corticectomized surgery. F3-effLuc within PLLA robustly adhered, and gradually increased luciferase signals of F3-effLuc within PLLA were detected in a day dependent manner. The implantation of F3-effLuc cells/PLLA complex into corticectomized rats showed longer-lasting luciferase activity than F3-effLuc cells alone. The bioluminescence signals from the PLLA-encapsulated cells were maintained for 14 days, compared with 8 days for the non-encapsulated cells. Immunostaining results revealed expression of the early neuronal marker, Tuj-1, in PLLA-F3-effLuc cells in the motor-cortex-ablated area. We observed noninvasively that the mechanical support by PLLA scaffold increased the survival of implanted neural stem cells in the corticectomized rat. The image-guided approach easily proved that scaffolds could provide supportive effect to implanted cells, increasing their viability in terms of enhancing therapeutic efficacy of stem-cell therapy.