Direct Cortical Electrostimulation Research Articles

Technique for intraoperative monitoring of corticospinal tract integrity using an electrode with a dynamic balloon

Aim. To present a technique for continuous monitoring of corticospinal tract integrity using an electrode with a dynamic balloon, examine the advantages and disadvantages of the selected and alternative monitoring techniques.Materials and methods. At the 1st stage, an electrode combined with a dynamic balloon was prepared. At the 2nd stage, continuous monitoring of the corticospinal tract using direct stimulation of the cortex using ballon grid during the main stage of cerebral surgery was performed. At the 3rd stage, interpretation of the obtained neurophysiological responses was performed.Results. The presented technique of continuous monitoring of the integrity of the corticospinal tract through direct cortical stimulation using the developed device prevents false response decreases which significantly helps with the interpretation of the obtained results and increases information value of the technique. The described technique is based on the presented clinical observations of intracerebral tumor resection, as well as microsurgical aneurysm clipping using the technique. During surgery, no false decrease of the neurophysiological signal amplitude was observed due to dynamic ballon inflation and maintenance of close contact between the electrode and the surface of the brain. A surgery performed using this technique allowed to achieve a favorable neurological outcome in a patient in the postoperative period.Conclusion. The presented device allows to perform continuous neuromonitoring using direct cortical electrostimulation with a strip electrode at any level of brain retraction. The technique decreases the risk of primary and secondary injury of the corticospinal and corticobulbar tracts which increases safety of neurosurgical intervention and decreases risks of neurological complications.

Awake Surgery With Visual Pathway Mapping in Low Grade Glioma Surgery

The visual pathway and its defects have been thoroughly studied in clinical correlation to temporal lobe lesions related to epilepsy and traumatic lesions. Nevertheless, its clinical correlation and other decision-making have not been addressed regarding neoplastic lesions. We present a case report of a 28-year-old man with a one-year history of generalized seizures and left superior homonymous quadrantanopia, with no other neurological disturbance on physical examination. According to diffusion tensor imaging tractography, MRI demonstrated a non-enhancing, right temporal lesion disrupting the visual pathway. An awake surgery with direct cortical electrostimulation of visual pathways was performed with subtotal resection of the tumor to preserve visual function, confirmed with postoperative MRI. Histopathological studies revealed a fibrillary astrocytoma.Surgical technique aided with intraoperative cortical and subcortical stimulation involving low-grade gliomas in eloquent areas is an exceptionally suitable procedure for complex cases where the visual pathway is compromised. Our objective is to describe how intraoperative mapping of visual function is performed in our institution and to comment on the relevant technical nuances, which can serve as a practical guideline for young neurosurgeons, as no previous cases have been reported in our country.

Two dissociable semantic mechanisms predict naming errors and their responsive brain sites in awake surgery. DO80 revisited

How do we choose words, and what affects the selection of a specific term? Naming tests such as the DO80 are frequently used to assess language function during brain mapping in awake surgery. The present study aimed to explore whether specific semantic errors become more probable under the stimulation of specific brain areas. Moreover, it meant to determine whether specific semantic characteristics of the items may evoke specific types of error. A corpus-based qualitative semantic analysis of the DO80 items, and the emitted naming errors to those items during direct cortical electrostimulation (DCE) revealed that the number of hyperonyms (i.e. 'vehicle' for car') of an item predicted the emission of a synonym ('automobile' for 'car'). This association occurred mainly in frontal tumor patients, which was corroborated by behavior to lesion analyses. In contrast, the emission of co-hyponyms was associated with tumors located in temporal areas. These two behavior-lesion associations thus dissociated, and were also dependent on item semantic characteristics. Co-hyponym errors might generate from the disruption in a temporal semantic-to-lexical process, and the production of synonyms could be the result of an impairment in a frontal lexical-selection mechanism. A hypothesis on the lexical selection mechanisms exerted by the inferior frontal gyrus is proposed. Crucially, the present data suggest the need for more restrictive naming tasks, with items conditioned by tumor location.

Functional magnetic resonance for the localization of eloquent areas in epilepsy surgery candidates: comparison to cortical electrostimulation mapping

IntroductionSurgical treatment for epilepsy comprises resective techniques in most patients.In those with epilepsy of sites close to highly specialized or eloquent areas, very precise anatomic delimitation is required. So far the most reliable method for anatomic localization of function is direct cortical electrostimulation mapping (CEM). Functional magnetic resonance (fMRI) is a non-invasive method that could also be used for this purpose. ObjectiveTo determine the sensitivity and specificity of fMRI for the identification of eloquent areas compared to CEM in epilepsy surgery candidates. MethodsFour patients who underwent presurgical fMRI and grid implantation in eloquent areas for epileptic focus localization with video-EEG were included in this study. Once the seizure onset site was identified, CEM was performed and a postsurgical structural magnetic resonance was reconstructed with Eclipse software to determine grid position. After correlating pre and postsurgical images, the site of the grid contacts where eloquent areas were identified was compared to localization by fMRI. ResultsOne hundred and twenty electrodes in six eloquent areas were evaluated and compared to location by fMRI: five hand motor areas and one language area in the temporal lobe. We found a global sensitivity of 0.86, specificity of 0.96, positive predictive value of 0.89, negative predictive value of 0.95 and accuracy of 0.94 for fMRI. ConclusionIn this study fMRI showed high specificity and proved to be useful for language lateralization. It is necessary to study this technique further, especially for language areas.

Electrical stimulation of the dorsolateral prefrontal cortex impairs semantic cognition

To identify the prefrontal cortical structures causally involved in verbal and nonverbal semantic cognition in both cerebral hemispheres. We retrospectively screened the intraoperative brain mapping data of 584 patients who underwent neurosurgery for neoplastic tumor under local anesthesia with direct cortical electrostimulation. Patients were included if they were right-handed, recently diagnosed with a diffuse low-grade glioma, and had a positive language mapping for verbal (naming task) and nonverbal (visual semantic association task) semantic cognition in the prefrontal cortex (n = 49). Among these, 30 were tested intraoperatively with both the naming and the semantic association tasks, while 19 were tested with the naming task only. Subsequently, each semantic site (n = 85) was plotted individually onto a common stereotaxic space for detailed analyses. The cortical sites associated with verbal semantic disturbances (n = 45) were distributed in the pars opercularis (n = 14) and pars triangularis (n = 19) of the left inferior frontal gyrus, and left dorsolateral prefrontal cortex (dlPFC, n = 12); only 2 sites were observed in the right dlPFC. In contrast, all but one cortical site associated with nonverbal semantic disturbances were observed in the left dorsolateral cortex (n = 8). In the right hemisphere, the same disturbances were found in the dlPFC (n = 14) and pars opercularis (n = 2). The present study demonstrated the critical role of the dlPFC in the semantic network, and indicated its specific and bilateral involvement in nonverbal semantic cognition in right-handers.

Reassessing lateralization in calculation.

The role of the left hemisphere in calculation has been unequivocally demonstrated in numerous studies in the last decades. The right hemisphere, on the other hand, had been traditionally considered subsidiary to the left hemisphere functions, although its role was less clearly defined. Recent clinical studies as well as investigations conducted with other methodologies (e.g. neuroimaging, transcranial magnetic stimulation and direct cortical electro-stimulation) leave several unanswered questions about the contribution of the right hemisphere in calculation. In particular, novel clinical studies show that right hemisphere acalculia encompasses a wide variety of symptoms, affecting even simple calculation, which cannot be easily attributed to spatial disorders or to a generic difficulty effect as previously believed. The studies reported here also show how the right hemisphere has its own specific role and that only a bilateral orchestration between the respective functions of each hemisphere guarantees, in fact, precise calculation. Vis-à-vis these data, the traditional wisdom that attributes to the right hemisphere a role mostly confined to spatial aspects of calculation needs to be significantly reshaped. The question for the future is whether it is possible to precisely define the specific contribution of the right hemisphere in several aspects of calculation while highlighting the nature of the cross-talk between the two hemispheres.This article is part of a discussion meeting issue 'The origins of numerical abilities'.

Balancing the 2 Hemispheres in Simple Calculation: Evidence From Direct Cortical Electrostimulation.

How do the parietal lobes contribute to simple calculation? Clinical and neuroimaging methods, which are based mainly on correlational evidence, have provided contrasting results so far. Here we used direct cortical electrostimulation during brain surgery to causally infer the role of the left and right parietal lobes in simple calculation. Stimulation provoked errors for addition and multiplication in different parietal areas on both hemispheres. Crucially, an innovative qualitative error analysis unveiled the functional contrast of the 2 parietal lobes. Right or left stimulation led to different types of substitution errors in multiplication, unveiling the function of the more active hemisphere. While inhibition of the left hemisphere led mainly to approximation errors, right hemisphere inhibition enhanced retrieval within a stored repertory. These results highlight the respective roles of each hemisphere in the network: rote retrieval of possible solutions by the left parietal areas and approximation to the correct solution by the right hemisphere. The bilateral orchestration between these functions guarantees precise calculation.

Editorial: Functional mapping

Direct cortical electrostimulation during brain surgery has been the basis of much of our understanding of functional regions of the cortex. The classic electrostimulation studies of Wilder Penfield and Herbert Jasper still guide our approaches to eloquent brain regions today. Direct cortical electrostimulation has also traditionally been the litmus test of whether neurological deficits would be incurred by tissue removal. This principle guides neurosurgeons removing lesions in the vicinity of languagebearing or sensorimotor cortex. It is also clear that removal of other known functional brain regions could result in specific neurological dysfunction (such as visual loss in occipital resection, alexia in dominant posterior temporal resection, and Gerstmann syndrome in dominant parietal lobe resection). The accompanying study by Della Puppa et al. documents an unexpected finding of mathematical processing dysfunction elicited by direct cortical electrostimulation of the nondominant parietal lobe, in the vicinity of the intraparietal sulcus.1 Data was obtained from 3 patients who were undergoing awake surgery of this area, and the authors found a reproducible dysfunction of multiplication and addition functions induced by direct cortical stimulation in the nondominant parietal lobe at relatively low amplitudes. These regions were spared and the patients had no deficit in mathematical processing postoperatively. Given that conventional wisdom holds that computational processing is housed in the dominant inferior parietal lobule, the results of this study contradict that widely held belief. Theirs is therefore an interesting and potentially important observation. It is not clear, however, that there is a 1-to-1 correlation between stimulation-induced function and focal deficit after resection. For example, the basal temporal lobe cortex on the dominant side commonly harbors language sites, yet resection of this area is routine in temporal lobe resections, and results in no detectable deficit. One must therefore interpret the results of the present study with caution. It must be remembered that mathematical processing—like many of the more complex brain functions—is likely a distributed function. The finding of a “node” in this network that could be stimulated and cause interruption in this function does not mean that this is the only such node, or even that it is a necessary one. Just like the basal temporal lobe and its relationship to language, it is possible that these areas in the nondominant parietal lobe could be safely resected despite the findings on direct cortical electrostimulation mapping. This study nicely illustrates a fairly highly localized area whose stimulation results in specific mathematical dysfunction. In order to improve our understanding of the significance of this finding, it should be followed up with focused functional MRI studies in an attempt to corroborate the significance of the direct cortical electrostimulation findings. Functional MRI could also help answer questions relating to the possibility of other brain regions involved in this function, and perhaps provide an answer to the question of where division and subtraction went. (http://thejns.org/doi/abs/10.3171/2013.4.JNS13560)

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.

Cortical areas involved in Arabic number reading

Distinct functional pathways for processing words and numbers have been hypothesized from the observation of dissociated impairments of these categories in brain-damaged patients. We aimed to identify the cortical areas involved in Arabic number reading process in patients operated on for various brain lesions. Direct cortical electrostimulation was prospectively used in 60 brain mappings. We used object naming and two reading tasks: alphabetic script (sentences and number words) and Arabic number reading. Cortical areas involved in Arabic number reading were identified according to location, type of interference, and distinctness from areas associated with other language tasks. Arabic number reading was sustained by small cortical areas, often extremely well localized (<1 cm(2)). Over 259 language sites detected, 43 (17%) were exclusively involved in Arabic number reading (no sentence or word number reading interference detected in these sites). Specific Arabic number reading interferences were mainly found in three regions: the Broca area (Brodmann area 45), the anterior part of the dominant supramarginal gyrus (Brodmann area 40; p < 0.0001), and the temporal-basal area (Brodmann area 37; p < 0.05). Diverse types of interferences were observed (reading arrest, phonemic or semantic paraphasia). Error patterns were fairly similar across temporal, parietal, and frontal stimulation sites, except for phonemic paraphasias, which were found only in supramarginal gyrus. Our findings strongly support the fact that the acquisition through education of specific symbolic entities, such as Arabic numbers, could result in the segregation and the specialization of anatomically distinct brain areas.