Passive functional mapping of receptive language areas using electrocorticographic signals

Objective

To validate the use of passive functional mapping using electrocorticographic (ECoG) broadband gamma signals for identifying receptive language cortex.

Electrocorticographic gamma activity during word production in spoken and sign language.

OBJECTIVE: To investigate the functional-neuroanatomic substrates of word production using signed versus spoken language. METHODS: The authors studied single-word processing with varying input and output modalities in a 38-year-old woman with normal hearing and speech who had become proficient in sign language 8 years before developing intractable epilepsy. Subdural electrocorticography (ECoG) was performed during picture naming and word reading (visual inputs) and word repetition (auditory inputs); these tasks were repeated with speech and with sign language responses. Cortical activation was indexed by event-related power augmentation in the 80- to 100-Hz gamma band, and was compared with general principles of functional anatomy and with subject-specific maps of the same or similar tasks using electrical cortical stimulation (ECS). RESULTS: Speech outputs activated tongue regions of the sensorimotor cortex, and sign outputs activated hand regions. In addition, signed word production activated parietal regions that were not activated by spoken word production. Posterior superior temporal gyrus was activated earliest and to the greatest extent during auditory word repetition, and the basal temporal-occipital cortex was activated similarly during naming and reading, reflecting the different modalities of input processing. With few exceptions, topographic patterns of ECoG gamma were consistent with ECS maps of the same or similar language tasks. CONCLUSIONS: Spoken and signed word production activated many of the same cortical regions, particularly those processing auditory and visual inputs; however, they activated different regions of sensorimotor cortex, and signing activated parietal cortex more than did speech. This study illustrates the utility of electrocorticographic gamma for studying the neuroanatomy and processing dynamics of human language.     

Electrocorticographic (ECoG) correlates of language. I. Desynchronization in temporal language cortex during object naming

The electrocorticogram (ECoG) was recorded during a language task, silent naming, from sites identified as essential for naming by electrical stimulation mapping and from surrounding cortex of left dominant temporal cortex at craniotomies under local anesthesia. The ECoG was analyzed quantitatively for a reduction in spectral density in 7-12 Hz frequencies indicating 'desynchronization.' These measurements were made on the averaged ECoG in 3 subjects and on individual ECoG segments in 4. Statistically significant increases in desynchronization were identified during silent naming at most sites essential for language, most often in the epoch from 700 to 1200 msec after presentation of the item to be named. During silent naming, there was a greater degree of desynchronization at those sites than in surrounding cortex. At several sites essential for language in several subjects, significantly less desynchronization was evident during a spatial task using physically identical stimuli. Thus, localized desynchronization in temporal cortex is an ECoG change with temporal, anatomic, and sometimes behavioral specificity to a language task. This finding provides insights into cortical physiologic mechanisms active during human language.     

Mismatch Between Electrocortical Stimulation and Electrocorticography Frequency Mapping of Language

BackgroundElectrocortical Stimulation Mapping (ESM) is the gold standard for mapping eloquent cortex in neurosurgery. This technique, however, can cause seizures and requires good patient cooperation. Electrocorticography (ECoG) could replace ESM. Several studies have directly compared ESM and ECoG frequency mapping of language cortex, with mixed results. This may be due to ECoG mapping typically being limited to one or a few language tasks, potentially leading to underestimation of language representation.ObjectiveTo evaluate the influence of the language task on the match between ECoG and ESM, we mapped language function based on episodes of spontaneous conversation with ECoG, and compared this with ESM data in eight epilepsy patients. A verb generation and picture naming task were used as reference standard.MethodsFrom the continuous ECoG and video registrations, periods of conversation were identified, distinguishing three conditions: speaking, listening and rest. A power-frequency analysis was done for each condition and the two language tasks. The match between ESM and ECoG frequency mapping was evaluated on the basis of sensitivity and specificity measures.ResultsECoG activation during spontaneous conversation and language tasks was seen in and around classic language areas. Comparing the electrodes activated in each condition with those indicated as language positive by ESM revealed that there was high specificity but relatively low sensitivity.ConclusionThe relatively poor match between ESM and ECoG mapping is not improved by using spontaneous language.     

Chasing language through the brain: Successive parallel networks

ObjectiveTo describe the spatio-temporal dynamics and interactions during linguistic and memory tasks.MethodsEvent-related electrocorticographic (ECoG) spectral patterns obtained during cognitive tasks from 26 epilepsy patients (aged: 9–60 y) were analyzed in order to examine the spatio-temporal patterns of activation of cortical language areas. ECoGs (1024 Hz/channel) were recorded from 1567 subdural electrodes and 510 depth electrodes chronically implanted over or within the frontal, parietal, occipital and/or temporal lobes as part of their surgical work-up for intractable seizures. Six language/memory tasks were performed, which required responding verbally to auditory or visual word stimuli. Detailed analysis of electrode locations allowed combining results across patients.ResultsTransient increases in induced ECoG gamma power (70–100 Hz) were observed in response to hearing words (central superior temporal gyrus), reading text and naming pictures (occipital and fusiform cortex) and speaking (pre-central, post-central and sub-central cortex).ConclusionsBetween these activations there was widespread spatial divergence followed by convergence of gamma activity that reliably identified cortical areas associated with task-specific processes.SignificanceThe combined dataset supports the concept of functionally-specific locally parallel language networks that are widely distributed, partially interacting in succession to serve the cognitive and behavioral demands of the tasks.     

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

ObjectiveThe purpose of this study was to improve the surgical treatment of epilepsy by maximising seizure control while protecting language function.MethodsA combined process of extra-operative electrical cortical stimulation (ECS) mapping, direct ECS and intra-operative continuous language assessment was performed during complicated operative cases. Of the 24 epilepsy patients, nine had a complex relationship between the seizure onset zone and the language cortices. The combined process was used in these nine patients. In the other 15 patients, surgical resection was completed based on extra-operative ECS results alone. Evaluations were performed before and after surgery to assess language function and seizure control.ResultsThe intra-operative continuous language assessment provided important information at the time of the resection. Seven extra-operative ECS positive language sites were resected without obvious language deficits in two patients. Resection was interrupted by language disturbances in an area where no extra-operative ECS positive site was identified in one patient. In three other patients, functional boundary was undefined in extra-operative ECS result, epileptogenic cortices were maximally resected during the continuous language assessment. In terms of seizure control, 18 of 24 (75%) patients reached Engel's class I, including all nine patients who underwent intra-operative continuous language assessment. One patient had minor surgery-related language deficits three months after resection.ConclusionsIntra-operative continuous language assessment proved to be complementary to extra-operative ECS mappings. The combination of ECS mappings and intra-operative continuous language assessment can maximise the resection of epileptogenic cortices and preserve language function in difficult cases involving the language cortex.     

Anatomical and functional distribution of functional MRI language mapping

ObjectiveThe aim of the present study was to compare localization of the language cortex using electrical cortical stimulation (ECS) and functional magnetic resonance imaging (fMRI) to establish the relevance of fMRI language mapping.MethodsLanguage mapping with fMRI and functional ECS mapping were retrospectively compared in ten patients with refractory epilepsy who underwent fMRI language mapping and functional ECS mapping between June 2012 and April 2019. A shiritori task, a popular Japanese word chain game, was used for fMRI language mapping.ResultsBOLD signal activation was observed in the left inferior frontal gyrus (including the pars opecularis and the pars triangularis), and superior temporal gyrus, which is a language-related area, as well as in the left superior and middle frontal gyri, the intraparietal sulcus, and fusiform gyrus. These results were compared with ECS to elucidate the functional role of the activated areas during fMRI language tasks. These activated areas included language areas, negative motor areas, supplementary motor areas (SMAs), and non-functional areas.ConclusionThe activated areas of fMRI language mapping include language-related areas, the negative motor area, and SMAs. These findings suggest the involvement of language and higher order motor networks in verbal expression.     

神经导航经颅磁刺激在癫痫术前语言区评估中的应用

目的探讨神经导航经颅磁刺激(n TMS)在术前皮质语言区评估中的临床应用价值。方法选取14例接受颅内硬膜下电极埋置术的癫痫患者,在神经导航引导下,采用4~10Hz重复经颅磁刺激(r TMS),对患者语言区进行定侧、定位分析。通过与颅内电极皮质电刺激(ECS)语言功能定位结果进行比较,评估nT MS在术前语言区定位中的临床应用价值。结果在14例患者中,nT MS诱发出明确语言停顿或明显语言干扰的患者12例,2例未出现明显语言干扰现象。术前nT MS诱发出语言障碍的12例患者,在ECS过程中均出现明确语言功能障碍。提高刺激强度可以提高诱发语言干扰的几率,频率4~6Hz刺激在语言区定位中,可以较好地兼顾患者的耐受性和刺激效果。结论对于不适合接受ECS等有创性评估的患者,术前nT MS可以提供有价值的语言功能定位信息。     

Right hemisphere language mapping in patients with bilateral language

PURPOSE: The configuration of language cortex in the dominant left hemisphere has been well described in the literature. However, language representation in the right hemisphere, particularly in patients with some degree of bilateral language, remains unclear. Herein, we report six patients who underwent electrocortical stimulation (ECS) for language mapping following implantation of a right subdural electrode array (SEA). METHODS: The medical records of six bilateral language patients with right SEA implantation at the Minnesota Epilepsy Group between January 1996 and July 2004 were retrospectively reviewed. Language lateralization was based on the results of the intracarotid amobarbital procedure performed preoperatively. Anatomical localization of the SEA for each patient was verified using colored photographs of the cortical surface before and after SEA placement and by review of MRI scans taken with the SEA in place. Frontal and temporal language areas were identified by errors in any language modality including automatic speech, reading, naming, repetition, and comprehension during ECS. RESULTS: Language maps revealed the presence of frontal and/or temporal language areas analogous to the classic essential language areas of the dominant left hemisphere in four of six patients. One patient had a widespread distribution of single-language-error sites over the right temporal lobe. One patient had a silent language map. CONCLUSION: Our results identified the presence of language cortex in the right hemisphere in five of six patients classified with bilateral language based on intracarotid amobarbital procedure. These areas are assumed to be accessory language zones in relation to the left hemisphere. Further exploratory studies are needed to evaluate their clinical significance.     

Functional dynamics of spoken and signed word production: A case study using electrocorticographic spectral analysis

Background: Event-related changes in the EEG power spectrum have recently been used to study functional brain activation in humans. Like traditional event-related potentials, event-related spectral changes provide information about the temporal evolution of cortical activation that is difficult to obtain with fMRI or PET. These spectral changes include event-related suppression of power in the alpha band (8-13 Hz) and even-related augmentation of power in the gamma band (>30 Hz). Most studies of the gamma band have focused on frequencies in and around 40 Hz. Using electrocorticographic (ECoG) signals recorded with subdural electrodes implanted for the surgical management of epilepsy, we have also observed a broadband augmentation of power in higher gamma frequencies (>80 Hz). This index of cortical activation has compared favourably with alpha suppression and with electrical cortical stimulation mapping in studies utilising simple motor and auditory processing, but such a comparison has not been done for tasks requiring more complex language processing. Aims: We used two different spectral indices of cortical activation - alpha power suppression and gamma power augmentation, to study the spatial and temporal patterns of human cortical activation during different word production tasks. Methods: Subdural ECoG electrodes were implanted for clinical purposes in a patient with normal hearing, who had learned sign language as an adult and later developed intractable epilepsy. We measured event-related spectral changes during language tasks with different input and output modalities: Picture naming and word reading (visual inputs), and word repetition (auditory input) were performed with spoken responses (oral-articulatory output) and with signed responses (manual-gestural output). In addition we used a visually guided motor task to map tongue and hand representations independent of language. Results: Speech and signing differentially activated tongue and hand regions of sensorimotor cortex. Although posterior superior temporal gyrus was activated early during auditory word repetition, picture naming and word reading also activated this region, albeit slightly later, consistent with phonological and/or lexical-semantic processing. In contrast, basal temporal-occipital cortex was activated earlier and with greater magnitude during picture naming and word reading than during word repetition, suggesting semantic processing or object and word recognition. In all of the tasks, event-related gamma augmentation occurred in more discrete spatial and temporal patterns than event-related alpha suppression. Conclusions: Event-related alpha suppression and gamma augmentation provide complementary information about task-related cortical activation. This study demonstrates the utility of ECoG spectral analysis for studying the functional anatomy of human language with excellent temporal resolution.     

粤语-普通话双语者语言功能区定位研究

目的探索粤-普双语者皮质语言区定位规律,研究双语者大脑手术语言功能的保护方法。方法对11例粤-普双语语言区胶质瘤病人进行语言区定位：术前应用BOLD-fMRI定位单纯图片命名（PN）及图片动词联想（VG）任务的双语语言区;术中唤醒下执行双语言任务,行直接皮质电刺激（DCES）语言区定位。结果DCES术中电刺激154个点,共获得阳性结果22个（14．3％）,其中确定特定语言区阳性点5个（3例）,均表现为单纯命名障碍,包括特定普通话语言区3个,特定粤语语言区2个。以DCES定位为金标准,BOLD-IMR／定位对VG任务的准确率明显高于PN任务（P=0．010）。结论术中DCES证实粤-普双语者存在特定语言区;粤-普早双语高度熟练者术前执行VG任务可提高BOLD-IMRI语言区定位的准确性;术前、术中行双语言任务定位语言区有助于保护双语病人的语言功能。     

Sentence translation in proficient bilinguals: a direct electrostimulation brain mapping

Direct cortical electrostimulation was used to study cortical areas hypothetically involved in translation in bilinguals during brain tumour resections, with a view to sparing these functional areas. A series of seven proficient bilingual patients was studied: two left-handed and five right-handed individuals with no pre-existing language deficit. Hemispheric cortex (on the side contralateral to the patient's hand-dominance) was directly stimulated whilst the patient performed naming and reading tasks in both languages and a translation task (of a written text from their second 'learned' language to their first or 'native' language). Of the 147 different cortical sites studied, 26 'language functional sites' were detected, where electrostimulation affected reading and/or naming in the patient's native and/or second learned language. Of these, 8 sites (in 4 patients) were "task-specific" and "language-specific" i.e., affecting only naming or reading in only one of the patient's languages. Of the 26 "language sites", only 3 produced any interferences in translation. All of these were located in frontal regions. Electrostimulation at these sites caused the patient to stop translating abruptly, but no language switching or other translation-related phenomenon was observed. No site was found that was involved only in translation and not other language tasks. Overall, in contrast to other language tasks, cortical structures of the convexity were rarely involved in translation. We suggest that translation interference could be more readily detected by subcortical stimulations. This spatial dissociation within the brain of translation function versus other language functions could explain the cases of dissociated language impairments observed in some bilingual patients with brain lesions. On a practical level, because the cortical sites found by translation tasks are few and related with other cortical language sites, we think that translation tasks provide little additional helpful information for cortical brain mapping in bilingual neurosurgical patients.     

Anatomic dissociation of auditory and visual naming in the lateral temporal cortex

BACKGROUND AND OBJECTIVE: Visual object naming traditionally has been used to identify cortical areas essential for naming (i.e., word retrieval), and investigators have found critical naming sites in the middle and posterior temporal region in most patients. Based on clinical observation, empirical findings, and the pathophysiology of temporal lobe epilepsy, the authors hypothesized that naming sites identified from auditory cues might also be relevant, and that within the temporal region, these sites would be anatomically distinct and located anterior to naming sites based on visual cues. METHODS: Twenty patients requiring resective surgery involving the left (language dominant) temporal lobe underwent pre-resection language mapping using direct cortical stimulation. Visual and auditory naming were tested at lateral temporal sites extending from 1 cm from the anterior tip to the parietal operculum. RESULTS: Auditory naming was consistently disrupted by stimulation in the anterior temporal lobe, whereas both auditory and visual naming were impaired by stimulation in the posterior temporal region. CONCLUSIONS: This pattern may explain why word finding difficulties sometimes arise or worsen following surgical procedures in which the anterior temporal region is resected without language mapping, or when resection is based on mapping that identifies language cortex exclusively using visual tasks. These results suggest that utilization of auditory based naming tasks might improve pre-resection identification of essential language cortex during direct stimulation cortical mapping, as well as noninvasive localization of dysfunction during presurgical cognitive testing.     

Increased gamma-range activity in human sensorimotor cortex during performance of visuomotor tasks.

OBJECTIVE: We documented changes in spectral power of human electrocorticograms (ECoG) during performance of sensorimotor tasks. METHODS: In 6 human subjects, ECoGs were recorded simultaneously from 14 subdural cortical sites in forearm sensorimotor cortex. The subjects performed 3 visuomotor tasks: tracking a moving visual target with a joystick-controlled cursor, threading pieces of tubing, and pinching the fingers sequentially against the thumb. Control conditions consisted of passive resting and active extension of the wrist. For each site the spectral power of the ECoG during these behaviors was computed for 5 10 Hz ranges between 10 and 60 Hz. RESULTS: All subjects showed power decreases in the range of 11-20 Hz and power increases in the 31-60 Hz range during performance of the visuomotor tasks, at sites in forearm sensorimotor cortex and adjacent areas. Simple wrist movements often produced little change in power. Three subjects showed episodes of explicit gamma oscillations during the visuomotor tasks. Different sites showed increases in gamma-range power for different tasks, indicating that the spatial distribution of the gamma activity is specific to the tasks. Cross-spectra showed that gamma activity could become synchronized between separate sites during particular tasks. CONCLUSIONS: Synchronized gamma-range activity in human sensorimotor cortex increases with performance of manipulative visuomotor tasks, supporting the hypothesis that coherent gamma oscillations may play a role in sensorimotor integration or attention.     

Evaluating the arcuate fasciculus with combined diffusion‐weighted MRI tractography and electrocorticography

The conventional model of language‐related brain structure describing the arcuate fasciculus as a key white matter tract providing a direct connection between Wernicke's region and Broca's area has been called into question. Specifically, the inferior precentral gyrus, possessing both primary motor (Brodmann Area [BA] 4) and premotor cortex (BA 6), has been identified as a potential alternative termination. The authors initially localized cortical sites involved in language using measurement of event‐related gamma‐activity on electrocorticography (ECoG). The authors then determined whether language‐related sites of the temporal lobe were connected, via white matter structures, to the inferior frontal gyrus more tightly than to the precentral gyrus. The authors found that language‐related sites of the temporal lobe were far more likely to be directly connected to the inferior precentral gyrus through the arcuate fasciculus. Furthermore, tractography was a significant predictor of frontal language‐related ECoG findings. Analysis of an interaction between anatomy and tractography in this model revealed tractrography to have the highest predictive value for language‐related ECoG findings of the precentral gyrus. This study failed to support the conventional model of language‐related brain structure. More feasible models should include the inferior precentral gyrus as a termination of the arcuate fasciculus. The exact functional significance of direct connectivity between temporal language‐related sites and the precentral gyrus requires further study. Hum Brain Mapp 35:2333–2347, 2014. © 2013 Wiley Periodicals, Inc .     

Multimodality language mapping in patients with left-hemispheric language dominance on Wada test

Objective

We determined the utility of electrocorticography (ECoG) and stimulation for detecting language-related sites in patients with left-hemispheric language-dominance on Wada test.

Methods

We studied 13 epileptic patients who underwent language mapping using event-related gamma-oscillations on ECoG and stimulation via subdural electrodes. Sites showing significant gamma-augmentation during an auditory-naming task were defined as language-related ECoG sites. Sites at which stimulation resulted in auditory perceptual changes, failure to verbalize a correct answer, or sensorimotor symptoms involving the mouth were defined as language-related stimulation sites. We determined how frequently these methods revealed language-related sites in the superior-temporal, inferior-frontal, dorsolateral-premotor, and inferior-Rolandic regions.

Results

Language-related sites in the superior-temporal and inferior-frontal gyri were detected by ECoG more frequently than stimulation (p < 0.05), while those in the dorsolateral-premotor and inferior-Rolandic regions were detected by both methods equally. Stimulation of language-related ECoG sites, compared to the others, more frequently elicited language symptoms (p < 0.00001). One patient developed dysphasia requiring in-patient speech therapy following resection of the dorsolateral-premotor and inferior-Rolandic regions containing language-related ECoG sites not otherwise detected by stimulation.

Conclusions

Language-related gamma-oscillations may serve as an alternative biomarker of underlying language function in patients with left-hemispheric language-dominance.

Significance

Measurement of language-related gamma-oscillations is warranted in presurgical evaluation of epileptic patients.     

Real‐time presurgical resting‐state fMRI in patients with brain tumors: Quality control and comparison with task‐fMRI and intraoperative mapping

Resting‐state functional magnetic resonance imaging (rsfMRI) is a promising task‐free functional imaging approach, which may complement or replace task‐based fMRI (tfMRI) in patients who have difficulties performing required tasks. However, rsfMRI is highly sensitive to head movement and physiological noise, and validation relative to tfMRI and intraoperative electrocortical mapping is still necessary. In this study, we investigate (a) the feasibility of real‐time rsfMRI for presurgical mapping of eloquent networks with monitoring of data quality in patients with brain tumors and (b) rsfMRI localization of eloquent cortex compared with tfMRI and intraoperative electrocortical stimulation (ECS) in retrospective analysis. Five brain tumor patients were studied with rsfMRI and tfMRI on a clinical 3T scanner using MultiBand(8)‐echo planar imaging (EPI) with repetition time: 400 ms. Moving‐averaged sliding‐window correlation analysis with regression of motion parameters and signals from white matter and cerebrospinal fluid was used to map sensorimotor and language resting‐state networks. Data quality monitoring enabled rapid optimization of scan protocols, early identification of task noncompliance, and head movement‐related false‐positive connectivity to determine scan continuation or repetition. Sensorimotor and language resting‐state networks were identifiable within 1 min of scan time. The Euclidean distance between ECS and rsfMRI connectivity and task‐activation in motor cortex, Broca's, and Wernicke's areas was 5–10 mm, with the exception of discordant rsfMRI and ECS localization of Wernicke's area in one patient due to possible cortical reorganization and/or altered neurovascular coupling. This study demonstrates the potential of real‐time high‐speed rsfMRI for presurgical mapping of eloquent cortex with real‐time data quality control, and clinically acceptable concordance of rsfMRI with tfMRI and ECS localization.     

Multi-component intrinsic brain activities as a safe alternative to cortical stimulation for sensori-motor mapping in neurosurgery

Objective

To assess the feasibility of multi-component electrocorticography (ECoG)-based mapping using “wide-spectrum, intrinsic-brain activities” for identifying the primary sensori-motor area (S1-M1).

皮层脑电图监测下手术治疗继发性癫痫

目的 探讨术中皮层脑电图(ECoG)监测下继发性癫痫的手术治疗效果.方法 选择自2004年9月至2008年1月贵州省人民医院收治的84例继发性癫痫患者行手术治疗,术中通过ECoG定位癫痫灶,显微手术切除原发病变,再根据癫痫发作的临床表现、病灶部位及ECoG监测所提示的异常脑电图波释放情况决定是否进行致痫灶切除及扩大致痫灶切除术,皮层热灼术,前颞叶切除术,海马、杏仁核切除术,胼胝体前部切开术.结果 84例患者切除病变前ECoG均可记录到癫痫波,原发病变切除后即时ECoG监测病变周围可记录到异常癫痫波80例,检出率为95.24%.其中13例致痫波发放区域位于非功能区者对该范围内皮层予以完全切除,术后即时ECoG提示癫痫波消失.67例位于或毗邻重要功能区者,采用低功率热灼该处皮层后,60例癫痫波消失.7例患者经联合胼胝体前部切开和(或)海马、杏仁核切除,术后即时ECoG监测效果满意.术后随访10个月～4年,按Engle标准评定疗效:Ⅰ级56例(66.67%),Ⅱ级21例(25.00%),Ⅲ级4例(4.76%),Ⅳ级3例(3.57%);手术总有效率为96.42%.结论 ECoG监测可明显提高手术治疗继发性癫痫的效果.

Abstract：

Objective To investigate the therapeutic effect of surgical management on patients with secondary epilepsy under the monitoring of cortical electrocorticography (ECoG). Methods Eighty-four patients with secondary epilepsy, admitted to our hospital from September 2004 to January 2008, were chosen; intraoperative ECoG monitoring was performed to locate the epileptic foci before the resection of the primary lesion. After the resection of primary lesion, resection of epileptic foci, enlarged resection of epileptic foci, cortical thermocoagulation, anterior temporal lobectomy,amygdalohippocampectomy and anterior callosotomy were performed, respectively, in different patients according to the clinical manifestations of seizures, and the locations of lesions and epileptic waveform discharges detected by intraoperative ECoG monitoring. Results The epileptic waveform discharges in 84 patients were noted before the resection of primary lesion. The epileptic waves were found in 80patients at the peripheral areas of the primary nidus under immediately postoperative ECoG monitoring,with a relevance ratio reaching 95.24%; after the resection of residual cortical zone with epileptic wave discharges, epileptic wave disappeared on immediately postoperative ECoG in 13 patients whose lesion located in nonfunctional area; normal signals were noted in 60 of the 67 patients performed cortical thermocoagulation whose cortical zone with epileptic wave discharges were located or neighbored in functional area, and good outcomes under the immediately postoperative ECoG monitoring were noted in the other 7 patients performed thermocoagulation combined with anterior callosotomy and/or amygdalohippocampectomy. The follow-up studies for 10 months to 4 years showed that grade Ⅰ in 56patients (66.67%), grade Ⅱ in 21 (25.00%), grade Ⅲ in 4 (4.76%) and grade Ⅳ in 3 (3.57%) according to the Engle standard of curative effect were achieved; the total effective rate was 96. 42%. Conclusion ECoG monitoring can significantly improve the efficiency of surgical management of secondary epilepsy.     

Dynamics of event-related causality in brain electrical activity

A new method (Event-Related Causality, ERC) is proposed for the investigation of functional interactions between brain regions during cognitive processing. ERC estimates the direction, intensity, spectral content, and temporal course of brain activity propagation within a cortical network. ERC is based upon the short-time directed transfer function (SDTF), which is measured in short EEG epochs during multiple trials of a cognitive task, as well as the direct directed transfer function (dDTF), which distinguishes direct interactions between brain regions from indirect interactions via brain regions. ERC uses new statistical methods for comparing estimates of causal interactions during prestimulus "baseline" epochs and during poststimulus "activated" epochs in order to estimate event-related increases and decreases in the functional interactions between cortical network components during cognitive tasks. The utility of the ERC approach is demonstrated through its application to human electrocorticographic recordings (ECoG) of a simple language task. ERC analyses of these ECoG recordings reveal frequency-dependent interactions, particularly in high gamma (>60 Hz) frequencies, between brain regions known to participate in the recorded language task, and the temporal evolution of these interactions is consistent with the putative processing stages of this task. The method may be a useful tool for investigating the dynamics of causal interactions between various brain regions during cognitive task performance.