Direct Cortical Electrical Stimulation Research Articles

Stimulation-Induced Seizures in Children Undergoing Stereo-EEG Evaluation.

This study reports our center's initial experience with the use of low-frequency stimulation in provoking stimulation-induced seizures (SIS) in children with drug-resistant epilepsy undergoing stereo-EEG evaluations. This retrospective study enrolled children aged 2 to 18 years with drug-resistant focal epilepsy who underwent stereo-EEG evaluation and extraoperative direct electrical cortical stimulation to elicit seizures. The low-frequency stimulation parameters consisted of biphasic square waveforms at frequency of 1 Hz, pulse width 1 millisecond, current 1 to 3 mA, and train duration of 20 seconds. Various epilepsy-related, imaging, neurophysiology, and surgery-related variables were collected and summarized. Fourteen children (mean age 13 years; 57.1% girls) were included, 10 of whom had unilateral stereo-EEG coverage. Cortical stimulation for provoking seizures was performed after a median of 5 days after electrode implantation. The median number of electrode-contacts stimulated per patient was 42. Four patients (28.6%) experienced habitual SIS (all extratemporal). The etiology in three patients was focal cortical dysplasia. Interictal high-frequency oscillations at electrode-contacts provoking SIS were observed in three cases (75%). Two of these individuals (50%) had class 1 International League Against Epilepsy seizure outcome at last follow-up, after the resection of the brain regions generating SIS. Low-frequency (1-Hz) stimulation could provoke habitual SIS in nearly one-fourth of children with focal epilepsy undergoing stereo-EEG monitoring. This study provides a limited pediatric experience with the low-frequency cortical stimulation and SIS.

Convergence of the arcuate fasciculus and third branch of the superior longitudinal fasciculus with direct cortical stimulation-induced speech arrest area in the anterior ventral precentral gyrus.

The objective was to identify the correspondence between the anterior terminations of the arcuate fasciculus (AF) and third branch of the superior longitudinal fasciculus (SLF-III) and the intraoperative direct cortical electrical stimulation (DCS)-induced speech arrest area. The authors retrospectively screened 75 glioma patients (group 1) who received intraoperative DCS mapping in the left dominant frontal cortex. To minimize the influence of tumors or edema, we subsequently selected 26 patients (group 2) with glioma or edema not affecting Broca's area, the ventral precentral gyrus (vPCG), and the subcortical pathways to generate DCS functional maps and to construct the anterior terminations of AF and SLF-III with tractography. Next, a grid-by-grid pairwise comparison was performed between the fiber terminations and the DCS-induced speech arrest sites to calculate Cohen's kappa coefficient (κ) in both groups 1 and 2. Finally, the authors also demonstrated the distribution of the AF/SLF-III anterior projection maps obtained in 192 healthy participants (group 3) and subsequently correlated these with the speech arrest sites in group 2 to examine their validity in predicting speech output area. The authors found that speech arrest sites were substantially consistent with SLF-III anterior terminations (group 1, κ = 0.64 ± 0.03; group 2, κ = 0.73 ± 0.05) and moderately consistent with AF (group 1, κ = 0.51 ± 0.03; group 2, κ = 0.49 ± 0.05) and AF/SLF-III complex (group 1, κ = 0.54 ± 0.03; group 2, κ = 0.56 ± 0.05) terminations (all p < 0.0001). The DCS speech arrest sites of the group 2 patients mainly (85.1%) emerged at the anterior bank of the vPCG (vPCGa). In group 3, both terminations of AF and SLF-III converged onto the vPCGa, and their terminations well predicted the DCS speech output area of group 2 (AF, area under the curve [AUC] 86.5%; SLF-III, AUC 79.0%; AF/SLF-III complex, AUC 86.7%). This study supports the key role of the left vPCGa as the speech output node by showing convergence between speech output mapping and anterior AF/SLF-III connectivity in the vPCGa. These findings may contribute to the understanding of speech networks and could have clinical implications in preoperative surgical planning.

A simultaneous intracranial EEG-surface EMG analysis of generalized tonic-clonic seizures (P10-1.004)

<h3>Objective:</h3> To analyze the neurophysiology of generalized tonic-clonic (GTC) seizures using intracranial-EEG and surface-EMG data. <h3>Background:</h3> The precise mechanism of a GTC seizure is not well understood. A polygraphic analysis with intracranial-EEG (iEEG) and surface-EMG (sEMG) offers a unique opportunity to study this mechanism from a neurophysiological standpoint. <h3>Design/Methods:</h3> We studied two patients with refractory focal epilepsy, admitted to the epilepsy-monitoring unit with iEEG and sEMG. Both patients underwent direct electrical cortical stimulation for cortical mapping. iEEG and EMG signals were recorded using Nihon-Kohden’s JE-120 256-channel amplifier with a sampling rate of 2000Hz. A GTC seizure was provoked in both patients during their respective stimulation sessions. <h3>Results:</h3> The tonic phase demonstrated continuous spike activity in iEEG with highest power in 50–100Hz range. The sEMG activity demonstrated an interference pattern in both agonists and antagonists, consistent with a tetanic contraction with a very similar power spectrum as the iEEG. The clonic phase was characterized by polyspike and slow-wave pattern. The polyspikes and slow-waves were time-locked with synchronized tetanic sEMG bursts and silent-periods in agonists and antagonists, respectively. The polyspikes were superimposed with ~400–600Hz high-frequency oscillations (HFOs). The frequency of the serrations of the motor unit potentials in the sEMG bursts was a subharmonic of the HFOs. The iEEG-sEMG latency was ~17–21ms, consistent with corticospinal conduction. There was a progressive increase of the sEMG burst and silent-period duration during the clonic phase, associated with corresponding increases in the polyspike and slow-wave durations. <h3>Conclusions:</h3> This study shows a very close relationship between iEEG and sEMG activity in a GTC seizure. The very similar power spectra of the iEEG and sEMG activities indicate that a GTC seizure is a direct result of cortical electrical activity varying in a crescendo-decrescendo manner. The transition from tonic to clonic phase is due to the “weakening” of the seizure discharge intensity. <b>Disclosure:</b> Dr. Acar has nothing to disclose. Dr. Ticku has nothing to disclose. Dr. Fotedar has nothing to disclose.

Overlap of functional and cytoarchitectonic maps in the human insula explored with intracranial EEG recordings and direct cortical electrical stimulation.

Overlap of functional and cytoarchitectonic maps in the human insula explored with intracranial EEG recordings and direct cortical electrical stimulation.

Motor Mapping of the Brain: Taniguchi Versus Penfield Method.

Intraoperative neurophysiological monitoring (IONM) techniques continue to prove useful as an adjunct in select surgeries for reducing the incidence of various postoperative deficits in motor function through the monitoring of motor evoked potentials (MEPs). The Penfield and Taniguchi methods of direct electrical cortical stimulation (DECS) stand in contrast to each other. Penfield’s method uses lower-frequency stimulation over a longer duration, while Taniguchi’s method uses a relatively higher frequency over a short duration. DECS motor mapping is considered suitable for tumor resections, aneurysm surgeries, arteriovenous malformation, and epilepsy surgeries. While subcortical motor mapping works efficiently with both methods, it aligns with Taniguchi’s method more effectively. Taniguchi’s method has a lower risk of seizures relative to Penfield’s method. While only cortical neurons are excited in Penfield’s stimulation technique, Taniguchi’s technique excites the whole corticospinal tract (CST), so it can be used for mapping in a stand-alone fashion. The Penfield technique remains the method of choice for language mapping. In all motor mapping, Train-of-Four (TOF) stimulation during the surgical procedure ensures that the patient’s muscles are not unduly relaxed.

Emerging Super-specialty of Neurology: Intraoperative Neurophysiological Monitoring (IONM) and Experience in Various Neurosurgeries at a Tertiary Care Hospital in Doha, Qatar.

IntroductionIntraoperative neurophysiological monitoring (IONM) helps in better patient outcomes by minimizing risks related to the functional status of the nervous system during surgical procedures. An IONM alert to the surgical team during the surgery can help them identify the cause and take immediate corrective action. IONM confers possible benefits, including improved surgical morbidity and mortality, better patient care, minimal neurological deficits, reduced hospital stay, medical costs, and litigation risk. In addition, a highly skilled IONM team will make a better patient outcome.MethodsWe retrospectively reviewed 62 consecutive patients who underwent intracranial and spinal neurosurgical procedures. Multimodality IONM was utilized, including somatosensory evoked potentials, transcranial electrical motor evoked potential, spontaneous and triggered electromyography, electroencephalography, electrocorticography, cortical sensory mapping, and direct electrical cortical stimulation. Of a total of 62 patients, two patients revealed neurotonic EMG discharges during IONM, and most patients woke up without any new neurological deficit.ResultsSixty-two patients were included, ranging from age 5 to 77 years (mean 43.5 years), with 54.8% men and 45.2% female. Multimodality IONM was used in all patients. Two EMG alerts were recorded during IONM, during a brain tumor resection, and right acetabular hip surgery with postoperative right foot drop.ConclusionMultimodality IONM is the gold standard of care for any surgical services and is used as real-time monitoring of functional integrity of neural structures at risk. If utilized by trained and expert teams, numerous surgeries may benefit from multimodality intraoperative neurophysiologic monitoring.

WS5.7. Mapping Methodologies

There are two main methodologies which can be used to assess the functional integrity of nervous system during intraoperative neurophysiological monitoring (IONM). Monitoring provides continuous real-time information about the functional integrity of the nervous tissue, whereas mapping provides rapid anatomical identification and localization of neural structures. Mapping of the primary motor cortex and subcortical corticospinal tract (CST) can be performed with direct cortical and subcortical electrical stimulation with a hand-held probe. Mapping of the central sulcus can be achieved by using phase reversal technique of somatosensory evoked potentials (SEP). This talk will be specifically focused on basic principles and application of these mapping methodologies and their usefulness mainly in brain tumor surgeries. Key Words: intraoperative neurophysiological monitoring (IONM), cortical mapping, subcortical mapping, central sulcus mapping

Reply: Broca's area: why was neurosurgery neglected for so long when seeking to re-establish the scientific truth? and Where is the speech production area? Evidence from direct cortical electrical stimulation mapping.

Gajardo-Vidal et al.1 reported data from a sample of 134 stroke patients with relatively circumscribed damage to the left frontal lobe. Contrary to the received view, mapping lesion to deficit using an ecologically-valid measure of speech production (i.e. spontaneous connected speech elicited with a picture description task) revealed that, irrespective of lesion extent, damage to Broca’s area does not contribute to long-term speech production outcome, whereas damage to the white matter in the vicinity of the anterior part of the arcuate fasciculus (AF) is strongly implicated. Our results therefore address a matter of critical clinical importance: understanding the causes of inter-patient variability in speech production outcome post-stroke.

Where is the speech production area? Evidence from direct cortical electrical stimulation mapping.

Where is the speech production area? Evidence from direct cortical electrical stimulation mapping.

Mapping of the Language Cortex.

Awake craniotomy with intraoperative neurophysiological language mapping (INLM) is an established procedure for patients undergoing surgery to resection tumors in the language cortex area. INLM and continuous neurophysiological monitoring allow assessment of the language function, which is not possible under general anesthesia. INLM of the brain areas provides a helpful tool to the operating surgeon in reducing the risks associated with tumor resection in the motor and language cortex. We present a literature review and the technical method used for INLM by utilizing direct electrical cortical stimulation. We also report the usefulness of INLM for evaluation of the language function during resection of cortical tumors, epilepsy foci, and arteriovenous malformations (AVMs) located near language areas. First, the central sulcus is identified by sensory mapping, followed by the motor cortex's identification by direct electrical cortical stimulation (DECS). Neurological assessment of the patient is done by auditory and visual feedback. The patient is asked to repeat numbers, days, words, sentences, read words, and name pictures during cortical stimulation. DECS may cause a slurring or speech arrest. Electrocorticography (ECoG) is also performed during cortical stimulation to identify any after-discharges. Examination of the patient occurs immediately after surgery, and then 24 hours, one week, six months, and 12 months postoperatively. Bipolar DECS for motor mapping with ECoG can safely and reliably be utilized to identify essential language areas with minimizing permanent language deficits and maximizing the extent of tumor resection.

Hemispheric asymmetries in visual mental imagery.

Visual mental imagery is the faculty whereby we can "visualize" objects that are not in our line of sight. Longstanding evidence dating back over thirty years has shown that unilateral brain lesions, especially in the left temporal lobe, can impair aspects of this ability. Yet, there is currently no attempt to identify analogies between these neuropsychological findings of hemispheric asymmetry and those from other neuroscientific approaches. Here, we present a critical review of the available literature on the hemispheric laterality of visual mental imagery, by looking at cross-method patterns of evidence in the domains of lesion neuropsychology, neuroimaging, and direct cortical stimulation. Results can be summarized under three main axes. First, frontoparietal networks in both hemispheres appear to be associated with visual mental imagery. Second, lateralization patterns emerge in the temporal lobes, with the left inferior temporal lobe being the most common finding in the literature for endogenously generated images, especially, but not exclusively, when orthographic material is used to ignite imagery. Third, an opposite pattern of hemispheric laterality emerges when visual mental images are induced by exogenous stimulation; direct cortical electrical stimulation tends to produce visual imagery experiences predominantly when applied to the right temporal lobe. These patterns of hemispheric asymmetry are difficult to reconcile with the dominant model of visual mental imagery, which emphasizes the implication of early sensory cortices. They suggest instead that visual mental imagery relies on large-scale brain networks, with a crucial participation of high-level visual regions in the temporal lobes.

SURG-09. EXTRAOPERATIVE CORTICAL MAPPING VIA IMPLANTED SUBDURAL AND DEPTH ELECTRODES FOR MAXIMIZING ELOQUENT AREA GLIOMA RESECTION

Abstract OBJECTIVE Aggressive, even supramarginal, resection without compromising the neurological status of the patient remains a great challenge in the management of glioma cases. Accurate cortical and subcortical functional mapping allows more radical glioma resection. Numerous imaging, electrophysiological, and hybrid methodologies have been employed in the cortical mapping of patients with gliomas in eloquent areas. Despite the recent advances of these non-invasive modalities, direct electrical cortical and subcortical stimulation and mapping through an awake craniotomy remains the gold standard for maximal glioma resection and preservation of eloquent cortex functions. Extraoperative stimulation and mapping via implanted subdural and/or depth electrodes may be a valid alternative mapping method in these cases that an awake procedure is not feasible. The role of this mapping method is examined in our current study. MATERIAL &amp; METHODS In a retrospective study, 51 patients undergoing extraoperative stimulation and mapping for glioma resection were included. The demographic data, the clinical characteristics, the stimulation parameters and complications, the extent of resection, the perioperative complications, and the tumor histological grade were analyzed. Shapiro-Wilk test, as well as uni- and multi-variate regression analysis was used for our statistical analysis. RESULTS The mean age of our participants was 58 (SD: 9.4) years. The location of the glioma was on the left side in 80.4%, while the frontal lobe was affected in 51.0%. Extraoperative cortical and subcortical stimulation and mapping was successful in 94.1%. The median stimulation procedure was 2.0 hours, while the median implantation time was 72 hours. Stimulation-induced seizures occurred in 13.7%, while CSF leakage in 5.9% of our cases. The mean extent of resection was 91.6%, while transient dysphasia occurred in 21.6%, and transient hemiparesis in 5.9% of our cases. CONCLUSIONS Extraoperative stimulation and mapping constitutes a valid alternative mapping option in glioma patients, who cannot undergo an awake craniotomy.

Application of direct electrical stimulation in awake craniotomy for glioma resection in the motor area

Objective To explore the effect of direct electrical stimulation in awake craniotomy for glioma resection in the motor area. Methods We conducted a retrospective analysis of clinical data of 34 patients with gliomas in the motor area who were admitted to Department of Neurosurgery, General Hospital of Southern Theatre Command from March 2015 to July 2017. The tumor was located in the left hemisphere in 16 patients and right hemisphere in 18. The gliomas were in supplementary motor area or premotor cortex in 23 cases, the central area in 9 cases, and supplementary motor area or premotor cortex invading the central area in 2 cases. All patients underwent awake craniotomy under general anesthesia. Neuronavigation and/or intraoperative ultrasound were employed to locate the lesion. Direct electrical stimulation was used for cortical and subcortical mapping of the important eloquent areas. The tumors were removed according to the functional boundary.Neural function and the degree of tumor resection were evaluated after operation. Results Of the 34 patients, 24 had a motor response after direct cortical electrical stimulation, 13 had abnormal sensations, and 10 revealed language-related cortices through mapping. For subcortical electrical stimulation, there were 24 cases of motor response, 1 case of abnormal sensation, and 8 cases of language disorders. A total of 30 cases (88.2%) of tumor removal reached functional boundaries, and subcortical electrical stimulation did not identify functional fiber in the remaining 4 (11.8%) cases which were all high-grade gliomas. Within 48 hours post surgery, the head MRI indicated total resection of tumor in 22 cases (64.7%), subtotal resection in 9 (26.5%), and partial resection in 3 (8.8%). The follow-up time of 34 patients was (23.6 ± 8.6) months (11.3-39.3)months.There were 29 cases (85.3%) which showed early postoperative neurofunctional disorders or worsening of pre-existing neurological deficits. Three cases (8.8%) developed late postoperative neurological dysfunction worse than preoperative conditions, of which 1 case was mild, 1 case was moderate and 1 case (2.9%) was severe. Of the 16 patients with preoperative neurological dysfunction or increased intracranial pressure, 13 had improved neurological function in 3 months after surgery, 2 were maintained in preoperative state and 1 had severe neurological deficits. Conclusions Functional mapping through direct electrical stimulation and continuous monitoring of the cortical and subcortical white fibers in the motor area during awake craniotomy could maximize the safe resection of glioma in the motor area, the incidence of long-term severe neurological deficits is low, and the quality of life could be improved after surgery. Key words: Glioma; Motor area; Supplementary motor area; Pyramid tract; Direct electrical stimulation

Four-dimensional map of direct effective connectivity from posterior visual areas

Lower- and higher-order visual cortices in the posterior brain, ranging from the medial- and lateral-occipital to fusiform regions, are suggested to support visual object recognition, whereas the frontal eye field (FEF) plays a role in saccadic eye movements which optimize visual processing. Previous studies using electrophysiology and functional MRI techniques have reported that tasks requiring visual object recognition elicited cortical activation sequentially in the aforementioned posterior visual regions and FEFs. The present study aims to provide unique evidence of direct effective connectivity outgoing from the posterior visual regions by measuring the early component (10–50 ​ms) of cortico-cortical spectral responses (CCSRs) elicited by weak single-pulse direct cortical electrical stimulation. We studied 22 patients who underwent extraoperative intracranial EEG recording for clinical localization of seizure foci and functionally-important brain regions. We used animations to visualize the spatiotemporal dynamics of gamma band CCSRs elicited by stimulation of three different posterior visual regions. We quantified the strength of CCSR-defined effective connectivity between the lower- and higher-order posterior visual regions as well as from the posterior visual regions to the FEFs. We found that effective connectivity within the posterior visual regions was larger in the feedforward (i.e., lower-to higher-order) direction compared to the opposite direction. Specifically, connectivity from the medial-occipital region was largest to the lateral-occipital region, whereas that from the lateral-occipital region was largest to the fusiform region. Among the posterior visual regions, connectivity to the FEF was largest from the lateral-occipital region and the mean peak latency of CCSR propagation from the lateral-occipital region to FEF was 26 ​ms. Our invasive study of the human brain using a stimulation-based intervention supports the model that the posterior visual regions have direct cortico-cortical connectivity pathways in which neural activity is transferred preferentially from the lower-to higher-order areas. The human brain has direct cortico-cortical connectivity allowing a rapid transfer of neural activity from the lateral-occipital region to the FEF.

The FAST graph: A novel framework for the anatomically-guided visualization and analysis of cortico-cortical evoked potentials

BackgroundIntracerebral electroencephalography (iEEG) using stereoelectroencephalography (SEEG) methodology for epilepsy surgery gives rise to complex data sets. The neurophysiological data obtained during the in-patient period includes categorization of the evoked potentials resulting from direct electrical cortical stimulation such as cortico-cortical evoked potentials (CCEPs). These potentials are recorded by hundreds of contacts, making these waveforms difficult to quickly interpret over such high-density arrays that are organized in three dimensional fashion. New MethodThe challenge in analyzing CCEPs data arises not just from the density of the array, but also from the stimulation of a number of different intracerebral sites. A systematic methodology for visualization and analysis of these evoked data is lacking. We describe the process of incorporating anatomical information into the visualizations, which are then compared to more traditional plotting techniques to highlight the usefulness of the new framework. ResultsWe describe here an innovative framework for sorting, registering, labeling, ordering, and quantifying the functional CCEPs data, using the anatomical labelling of the brain, to provide an informative visualization and summary statistics which we call the “FAST graph” (Functional-Anatomical STacked area graphs). The FAST graph analysis is used to depict the significant CCEPs responses in patient with focal epilepsy. ConclusionsThe novel plotting approach shown here allows us to visualize high-density stimulation data in a single summary plot for subsequent detailed analyses. Improving the visual presentation of complex data sets aides in enhancing the clinical utility of the data.

High resolution passive speech mapping in dominant hemisphere glioma surgery

Background.Intraoperative brain mapping is one of the most critical stages of neurosurgical intervention in the eloquent area of the cerebral cortex. Traditionally direct cortical electrical stimulation is used for these purposes, but it can lead to seizures and loss of consciousness that makes it impossible to continue the procedure. Moreover, it significantly changes the surgery plan, especially in case of speech mapping during awake craniotomy.The study objectiveis to create a setup for intraoperative eloquent cortical areas passive mapping, and to compare informativity and safety of passive and active speech mapping.Materials and methods.We have created and tested a mobile device for high-resolution mapping of the Broca’s area that uses the analysis of the desynchronization processes in high-gamma oscillations in 64 micro-contact grid electrode for electrocorticography during awake craniotomy when patient pronounces the objects and actions.Results.We found precise coincidence for localization of the Broca’s area, determined by analyzing of bioelectric signal obtained from the electrocorticography and cortical mapping performed by bipolar direct cortical stimulation using Penfield method.Conclusion.The passive cortical speech mapping expands the potentialities of neurosurgical operations in the eloquent area of the brain and can increase the number of patients for whom this study is achievable. Further studies needed to evolve algorithms and sets of stimuli to expand the list of functional zones that can be mapped passively.

Technical considerations for generating somatosensation via cortical stimulation in a closed-loop sensory/motor brain-computer interface system in humans

Somatosensory feedback is the next step in brain computer interface (BCI). Here, we compare three cortical stimulating array modalities for generating somatosensory percepts in BCI. We compared human subjects with either a 64-channel “mini”-electrocorticography grid (mECoG; 1.2-mm diameter exposed contacts with 3-mm spacing, N = 1) over the hand area of primary somatosensory cortex (S1), or a standard grid (sECoG; 1.5-mm diameter exposed contacts with 1-cm spacing, N = 1), to generate artificial somatosensation through direct electrical cortical stimulation. Finally, we reference data in the literature from a patient implanted with microelectrode arrays (MEA) placed in the S1 hand area. We compare stimulation results to assess coverage and specificity of the artificial percepts in the hand. Using the mECoG array, hand mapping revealed coverage of 41.7% of the hand area versus 100% for the sECoG array, and 18.8% for the MEA. On average, stimulation of a single electrode corresponded to sensation reported in 4.42 boxes (range 1–11 boxes) for the mECoG array, 19.11 boxes (range 4–48 boxes) for the sECoG grid, and 2.3 boxes (range 1–5 boxes) for the MEA. Sensation in any box, on average, corresponded to stimulation from 2.65 electrodes (range 1–5 electrodes) for the mECoG grid, 3.58 electrodes for the sECoG grid (range 2–4 electrodes), and 11.22 electrodes (range 2–17 electrodes) for the MEA. Based on these findings, we conclude that mECoG grids provide an excellent balance between spatial cortical coverage of the hand area of S1 and high-density resolution.

Chapter 20 - Electrocorticography and functional mapping

Brain mapping is often critical to the success of epilepsy and brain tumor surgeries. Mapping the cerebral cortex can be performed either extraoperatively or intraoperatively. When considering the optimal venue for a particular patient, a number of important considerations need to be considered including: the intended goals for the mapping, patient factors, anesthetic effects, stimulation parameters, cortical functions of interest, as well as the mapping modalities being considered. In this chapter, we will cover electrocorticography, cortical somatosensory evoked potentials, and the various neurophysiologic techniques used to map sensorimotor and cognitive functions, including language. One of the main uses of electrocorticography in epilepsy surgery is to map the cortical regions associated with epileptiform activity. This information is used to plan resection boundaries. Electrocorticography can also be used to monitor for afterdischarges (ADs) during direct cortical stimulation as well as for mapping high-frequency activity during various cognitive tasks. Cortical somatosensory evoked potentials can identify the central sulcus by mapping the dipolar activation of the primary somatosensory cortex that results from stimulation of the large fiber somatosensory pathway by peripheral nerve stimulation. Motor, sensory, and language cortex can also be identified by direct electrical cortical stimulation.

Probabilistic electrical stimulation mapping of human medial frontal cortex

The medial frontal cortex remains functionally ill-understood; this is reflected by the heterogeneity of behavioural outcomes following damage to the region. We aim to use the rich information provided by extraoperative direct electrical cortical stimulation to enhance our understanding of its functional anatomy.Examining a cohort of 38 epilepsy patients undergoing direct electrical cortical stimulation in the context of presurgical evaluation, we reviewed stimulation findings and classified them in a behavioural framework (positive motor, negative motor, somatosensory, speech disturbances, and “other”). The spatially discrete cortical stimulation-derived data points were then transformed into continuous probabilistic maps, thereby enabling the voxel-wise spatial inference widely used in the analysis of functional and structural imaging data.A functional map of stimulation findings of the medial wall emerged. Positive motor responses occurred in 141 stimulations (31.2%), anatomically located on the paracentral lobule (threshold at p<.05), extending no further than the vertical anterior commissure (VCA) line. Thirty negative motor responses were observed (6.6%), localised to the VCA line (at p < .001 uncorrected). In 43 stimulations (9.5%) a somatosensory response localised to the caudal cingulate zone (at p < .001 uncorrected), with a second region posterior to central sulcus. Speech disturbances were elicited in 38 stimulations (8.4%), more commonly but not exclusively from the language fMRI dominant side, just anterior to VCA (p < .001 uncorrected). In only 2 stimulations, the patient experienced a subjective “urge” to move in the absence of overt movement.Classifying motor behaviour along the dimensions of effector, and movement vs arrest, we derive a wholly data-driven stimulation map of the medial wall, powered by the largest number of stimulations of the region reported (n = 452) in patients imaged with MRI. This model and the underlying data provide a robust framework for understanding the architecture of the region through the joint analysis of disruptive and correlative anatomical maps.

Awake craniotomy using dexmedetomidine and scalp blocks: a retrospective cohort study.

Anesthetic and surgical considerations for awake craniotomy (AC) include airway patency, patient comfort, and optimization of real-time brain mapping. The purpose of this study is to report our experience of using dexmedetomidine and scalp blocks, without airway intervention, as a means to facilitate and optimize intraoperative brain mapping and brain tumour resection during AC. We conducted a retrospective cohort study of 55 patients who underwent AC from March 2012 to September 2016. The incidence of critical airway outcomes, perioperative complications, and successful intraoperative mapping was determined. The primary outcome was the incidence of a failed AC anesthetic technique as defined by the need to convert to general anesthesia with a secured airway prior to (or during) brain mapping and brain tumour resection. Secondary outcomes were the intraoperative incidence of: 1) altered surgical management due to information acquired through real-time brain mapping, 2) interventions to restore airway patency or rescue the airway, 3) hemodynamic instability (> 20% from baseline), 4) nausea and vomiting, 5) new onset neurologic deficits, and 6) seizure activity. There were no anesthesia-related critical events and no patients required airway manipulation or conversion to a general anesthetic. Multimodal language, motor, and sensory assessment with direct cortical electrical stimulation was successfully performed in 100% of cases. In 24% (13/55) of patients, data acquired during intraoperative brain mapping influenced surgical decision-making regarding the extent of tumour resection. Nine (16%) patients had intraoperative seizures. Dexmedetomidine-based anesthesia and scalp block facilitated AC surgery without any requirement for urgent airway intervention or unplanned conversion to a full general anesthetic. This approach can enable physiologic testing before and during tumour resection facilitating real-time surgical decision-making based on intraoperative brain mapping with patients awake thereby minimizing the risk of neurologic deficit and increasing the opportunity for optimal surgical resection.