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• The number of corticocortical evoked potentials decreases under anesthesia compared to the awake state. • The N1-peak latency is increased under propofol-anesthesia. • The topology of effective networks in awake patients is preserved under anesthesia. We compared the effective networks derived from Single Pulse Electrical Stimulation (SPES) in intracranial electrocorticography (ECoG) of awake epilepsy patients and while under general propofol-anesthesia to investigate the effect of propofol on these brain networks. We included nine patients who underwent ECoG for epilepsy surgery evaluation. We performed SPES when the patient was awake (SPES-clinical) and repeated this under propofol-anesthesia during the surgery in which the ECoG grids were removed (SPES-propofol). We detected the cortico-cortical evoked potentials (CCEPs) with an automatic detector. We constructed two effective networks derived from SPES-clinical and SPES-propofol. We compared three network measures (indegree, outdegree and betweenness centrality), the N1-peak-latency and amplitude of CCEPs between the two effective networks. Fewer CCEPs were observed during SPES-propofol (median: 6.0, range: 0–29) compared to SPES-clinical (median: 10.0, range: 0–36). We found a significant correlation for the indegree, outdegree and betweenness centrality between SPES-clinical and SPES-propofol (respectively r s = 0.77, r s = 0.70, r s = 0.55, p < 0.001). The median N1-peak-latency increased from 22.0 ms during SPES-clinical to 26.4 ms during SPES-propofol. Our findings suggest that the number of effective network connections decreases, but network measures are only marginally affected. The primary network topology is preserved under propofol. [ABSTRACT FROM AUTHOR]

• Direct stimulation affected the subregions responsible for cognitive processes. • Cognitive processes were linked to changes in gamma power. • Direct cortical stimulation has the potential to enhance cognitive processes. This study aims to investigate the potential of direct cortical stimulation (DCS) to modulate tactile categorization and decision-making, as well as to identify the specific locations where these cognitive functions occur. We analyzed behavioral changes in three epilepsy patients with implanted electrodes using electrocorticography (ECoG) and a vibrotactile discrimination task. DCS was applied to investigate its impact on tactile categorization and decision-making processes. We determined the precise location of the electrodes where each cognitive function was modulated. This functional discrimination was related with gamma band activity from ECoG. DCS selectively affected either tactile categorization or decision-making processes. Tactile categorization was modulated by stimulating the rostral part of the supramarginal gyrus, while decision-making was modulated by stimulating the caudal part. DCS can enhance cognitive processes and map brain regions responsible for tactile categorization and decision-making within the supramarginal gyrus. This study also demonstrates that DCS and the gamma activity of ECoG can concordantly identify the detailed brain mapping in a tactile process compared to other functional neuroimaging. The combination of DCS and ECoG gamma activity provides a more nuanced and detailed understanding of brain function than traditional neuroimaging techniques alone. [ABSTRACT FROM AUTHOR]

• Hemorrhage was found in 11% cases regardless of clinical symptoms and should be recognized to avoid mis-localization of seizure onset zones. • sEEG recordings in close proximity of hemorrhage may have electrographic correlates to identify hemorrhage during monitoring. • Despite the occurrence of hemorrhage, when surgical treatments were pursued, a vast majority of patients had favorable outcomes. Intracranial hemorrhage (ICH) is a known complication during stereo-electroencephalography (sEEG) however true rates remain unknown. We provide a comprehensive review of ICH during sEEG regardless of clinical symptoms. Secondly, we analyzed sEEG recordings to identify electrographic correlates of ICH. This is a retrospective study of patients undergoing sEEG between January 2016 and April 2022 at the Mayo Clinic in Rochester. We reviewed medical records and imaging studies to identify ICH. We analyzed ICH by type, electrode trajectories, timing, sEEG findings and outcomes. There were a total of 201 sEEG implants, of which 23 (11%) cases or 0.9% electrodes implanted had evidence of ICH. The majority of affected patients (82%) were either asymptomatic or had mild clinical neurological manifestations. In 90% of patients who proceeded with surgical treatments, outcomes were favorable. The most common sEEG finding in contacts in proximity of ICH was either focal slowing with interictal discharges or focal electrographic seizures. ICH associated with sEEG is likely under-reported in literature. We present electroencephalographic correlates of ICH that may aid identification of ICH in the course of performing sEEG monitoring. Our data provides clinically relevant information on potential risks and outcomes of ICH. Furthermore, our findings aid identification of ICH during sEEG. [ABSTRACT FROM AUTHOR]

• Low and high frequency band power measured with chronic electrocorticography in people with locked-in syndrome spatially matches pre-surgical fMRI. • fMRi is useful for finding brain regions likely to yield good BCI control. • If additional BCI studies confirm these results, future studies may rely on fMRI to localize target areas for BCI implantation. Electrocorticography (ECoG)-based brain-computer interface (BCI) systems have the potential to improve quality of life of people with locked-in syndrome (LIS) by restoring their ability to communicate independently. Before implantation of such a system, it is important to localize ECoG electrode target regions. Here, we assessed the predictive value of functional magnetic resonance imaging (fMRI) for the localization of suitable target regions on the sensorimotor cortex for ECoG-based BCI in people with locked-in syndrome. Three people with locked-in syndrome were implanted with a chronic, fully implantable ECoG-BCI system. We compared pre-surgical fMRI activity with post-implantation ECoG activity from areas known to be active and inactive during attempted hand movement (sensorimotor hand region and dorsolateral prefrontal cortex, respectively). Results showed a spatial match between fMRI activity and changes in ECoG low and high frequency band power (10 – 30 and 65 – 95 Hz, respectively) during attempted movement. Also, we found that fMRI can be used to select a sub-set of electrodes that show strong task-related signal changes that are therefore likely to generate adequate BCI control. Our findings indicate that fMRI is a useful non-invasive tool for the pre-surgical workup of BCI implant candidates. If these results are confirmed in more BCI studies, fMRI might be used for more efficient surgical BCI procedures with focused cortical coverage and lower participant burden. [ABSTRACT FROM AUTHOR]

• Cognitive tasks (attention to task instructions, then task performance) can end afterdischarges caused by cortical stimulation. • Electrocorticographic coherence decreases progressively with these tasks, returning towards baseline when afterdischarges end. • These decreases may be due to emergent properties of the brain as a whole which might help modify seizures and other disorders. We previously studied efficacy of cognitive tasks on afterdischarge termination in patients undergoing cortical stimulation and found that diffuse wavelet cross-coherence changes on electrocorticography were associated with termination efficacy. We now report wavelet cross-coherence findings during different time segments of trials during which afterdischarges ended. For 12 patients with implanted subdural electrodes, we compared wavelet cross-coherence findings among several 1-second portions of cognitive tasks, reflecting task presentation, patient replies, and afterdischarge termination. Coherence decreased significantly and progressively over time for 16.89, 22.53, and 30.03 Hz frequency ranges, but increased with afterdischarge termination. Coherence first increased, and then decreased for the 7.13 Hz frequency range. The findings suggest that cumulative but non-specific factors, likely related primarily to attention, influence the coherence results throughout the task, with a separate effect due to resolution of the afterdischarges at the end. Task performance is well known to localize to specific brain regions and to be restricted in timing. In contrast, attention and overall mental activation might be due to emergent properties of brain as a whole and that are less circumscribed in space or time. Cognitive tasks might modify seizures and other neurological disorders. [ABSTRACT FROM AUTHOR]

• During brain surgery, the measurement of axono-cortical evoked potentials can allow exploring the neural connectivity on-line. • Electrical stimulation on the white matter tracts were applied while recording the evoked response at the cortical level. • The 'hottest' spot with a direct connection to the stimulation site can be distinguished from the neighboring activity. Intraoperative measurement of axono-cortical evoked potentials (ACEP) has emerged as a promising tool for studying neural connectivity. However, it is often difficult to determine if the activity recorded by cortical grids is generated by stimulated tracts or by spurious phenomena. This study aimed to identify criteria that would indicate a direct neurophysiological connection between a recording contact and a stimulated pathway. Electrical stimulation was applied to white matter fascicles within the resection cavity, while the evoked response was recorded at the cortical level in seven patients. By analyzing the ACEP recordings, we identified a main epicenter characterized by a very early positive (or negative) evoked response occurring just after the stimulation artifact (<5 ms, |Amplitude| > 100 µV) followed by an early and large negative (or positive) monophasic evoked response (<40 ms; |Amplitude| > 300 µV). The neighboring activity had a different waveform and was attenuated compared to the hot-spot activity. It is possible to distinguish the hotspot with direct connectivity to the stimulated site from neighboring activity using the identified criteria. The electrogenesis of the ACEP at the hotspot and neighboring activity is discussed. [ABSTRACT FROM AUTHOR]

• We performed a prospective multicenter medical device study. • Polymer strips with embedded metal nanoparticles had lower impedance than the comparator device. • The electrodes achieved good signal-to-noise-ratio. During neurosurgical procedures, strip electrodes should have low impedance and sufficient adherence on the brain surface. We evaluated the signal quality, safety, and performance of a novel strip electrode (WISE Cortical Strip, WCS®), with conductive electrode contacts created with platinum nanoparticles embedded in a polymer base. In a multicenter interventional, non-inferiority study, we compared WCS to a conventional strip electrode (Ad-Tech). We recorded impedance and somatosensory evoked potentials (SEP) and determined the signal-to-noise ratio (SNR). We performed direct stimulation of the motor cortex. An external clinical event committee rated safety and adverse events and users rated usability. During 32 brain surgeries in the paracentral region, WCS was rated safe and effective in signal transmission. Two seizure events were classified as probably related to the stimulation with WCS. The users rated WCS adhesion to the brain as satisfactory but reported difficulties sliding the WCS under the dura. The median (IQR) impedance of WCS was lower than for Ad-Tech: 2.7 (2.3–3.7) vs 5.30 (4.3–6.6) kΩ (p < 0.005). The SNR of SEP was non-inferior for WCS compared to Ad-Tech. The impedance of WCS was lower than Ad-Tech without safety limitations. In small craniotomies not exposing the motor cortex its use may be limited. Low impedance electrodes facilitate recordings with high SNR. [ABSTRACT FROM AUTHOR]

• The relevance of invasive neurophysiology in DBS patients is described. • Practical aspects of DBS recordings are introduced. • An outlook on the future of DBS neurophysiology is provided. Deep brain stimulation (DBS) offers the unique opportunity to record human neural population activity as multiunit activity and local field potentials (LFP) directly from the target area in the depth of the brain. This has led to important discoveries through characterization of pathological activity patterns and identification of motor and cognitive correlates of basal ganglia function in patients with movement disorders. These findings have been covered extensively in a large body of literature, but the technical aspects of microelectrode and LFP recordings in DBS patients are rarely reported. This review summarizes the experience from invasive neurophysiology experiments in over 500 DBS cases in the last 20 years in a single centre. It introduces the basics of intraoperative microelectrode recordings, discusses the neurophysiological and technical aspects of LFP signals and gives and outlook on current and next-generation developments - from sensing enabled implantable devices to combined electrocorticography and LFP recordings during adaptive DBS. [ABSTRACT FROM AUTHOR]

• When cognitive effort ends afterdischarges, there are widespread changes in coherence. • These coherence changes are similar throughout the cortex, regardless of the distance between recorded sites. • This similarity suggests a pan-cortical effect that may complement the activity of regional and multiregional networks. It is well known that activity in, or coordination among, brain regions, can underlie movement, sensation, language, and cognition but there are observations that tasks unrelated to specific brain regions can nonetheless alter activity in those regions. These tasks might invoke activity in multiregional networks, but it also is possible that they are associated with changes beyond these networks. We therefore evaluated the possibility that more widespread, or even whole-cortical, mechanisms might complement or alter focal or multifocal cortical activity. We assessed the extent of electroencephalographic changes occurring outside areas with epileptiform activity, but that were associated with termination of the epileptiform activity. To do this, we measured the distribution of wavelet cross-coherence changes based on electrocorticography from 15 patients who showed regional afterdischarges in response to electrical brain stimulation prior to epilepsy surgery and in whom cognitive tasks were used in attempts to end the afterdischarges. There were 1276 electrodes implanted in these patients, and we analyzed a total of 55,494 electrode combinations. We compared recordings when cognitive effort was versus when it was not successful in ending afterdischarges. We found that when afterdischarges were suppressed there were changes in electrocorticographic coherence that were similar throughout cortex, regardless of the distance between sites. The similarity implies coordination of the changes, and the similarity regardless of distance or location implies a pan-cortical effect. Our results provide physical support for hypotheses that pan-cortical processes complement the well-known regional and multiregional networks. These processes may participate in, be recruited by, modify, or underlie the conative experiences of waking life. [ABSTRACT FROM AUTHOR]

• Reaction times in Parkinson Disease (PD) patients are faster when action selection is externally cued (EC) relative to self-initiated or internally cued (IC). • Posterior parietal cortex and lateral premotor cortex connectivity is greater during EC relative to the IC action selection. • Delayed action initiation seen in PD patients may be corrected with visuospatial cuing through engagement of dorsal visual stream. In patients with Parkinson Disease (PD), self-initiated or internally cued (IC) actions are thought to be compromised by the disease process, as exemplified by impairments in action initiation. In contrast, externally-cued (EC) actions which are made in response to sensory prompts can restore a remarkable degree of movement capability in PD, particularly alleviating freezing-of-gait. This study investigates the electrophysiological underpinnings of movement facilitation in PD through visuospatial cuing, with particular attention to the dynamics within the posterior parietal cortex (PPC) and lateral premotor cortex (LPMC) axis of the dorsal visual stream. Invasive cortical recordings over the PPC and LPMC were obtained during deep brain stimulation lead implantation surgery. Thirteen PD subjects performed an action selection task, which was constituted by left or right joystick movement with directional visual cuing in the EC condition and internally generated direction selection in the IC condition. Time-resolved neural activities within and between the PPC and LPMC were compared between EC and IC conditions. Reaction times (RT) were significantly faster in the EC condition relative to the IC condition (paired t-test, p = 0.0015). PPC-LPMC inter-site phase synchrony within the β-band (13–35 Hz) was significantly greater in the EC relative to the IC condition. Greater PPC-LPMC β debiased phase lag index (dwPLI) prior to movement onset was correlated with faster reaction times only in the EC condition. Multivariate granger causality (GC) was greater in the EC condition relative to the IC condition, prior to and during movement. Relative to IC actions, we report relative increase in inter-site phase synchrony and directional PPC to LPMC connectivity in the β-band during preparation and execution of EC actions. Furthermore, increased strength of connectivity is predictive of faster RT, which are pathologically slow in PD patients. Stronger engagement of the PPC-LPMC cortical network by an EC specifically through the channel of β-modulation is implicated in correcting the pathological slowing of action initiation seen in Parkinson's patients. These findings shed light on the electrophysiological mechanisms that underlie motor facilitation in PD patients through visuospatial cuing. [ABSTRACT FROM AUTHOR]

• Hippocampus-sparing lesionectomy can achieve excellent seizure outcomes in lesional TLE with a normal hippocampus on MRI. • Complete resection of lesion is associated with good seizure outcomes. • Spikes and high-frequency oscillations in the normal-looking hippocampus were common and not associated with poor seizure outcome. We investigated hippocampal-sparing lesionectomy (HSL) outcomes in temporal lobe epilepsy (TLE) and the significance of high-frequency oscillations (HFOs) detected by hippocampography in HSL. We retrospectively reviewed data from patients who underwent HSL for lesional TLE. Patients were included when MRI confirmed (i) a lesion limited to the temporal lobe with normal hippocampi preoperatively and (ii) hippocampal integrity postoperatively. Factors possibly related to outcomes were collected. Intraoperative hippocampography was reviewed, and spikes, ripples, and fast ripples were marked. Seizure outcomes were tracked ≥ 2 years. Postoperative neuropsychological tests were performed and analyzed. We included 67 patients (35 males/32 females, median age at surgery 28 years, 57 seizure-free). Complete resection was significantly associated with being seizure-free without aura, an outcome achieved by 32 (69.6%) patients with complete resection vs 1 (12.5%) with incomplete resection (p = 0.004). Spikes/ripples/fast ripples appeared frequently in the hippocampus, occurring in 86.4%/82.4%/75.0% of cases before resection and 76.7%/78.1%/63.0% after resection. The presence and rate were unconnected to seizure outcome. Postoperative neuropsychological outcomes in intelligence and visual memory improved overall. HSL in lesional TLE can produce satisfactory seizure and cognitive outcomes. Intraoperative hippocampography-guided resection of apparently normal hippocampi should be performed cautiously and might not be necessary. This study provided evidence in decision making for patients with lesional TLE with a radiologically normal hippocampus. [ABSTRACT FROM AUTHOR]

• High-frequency (gamma) electrocorticographic activity indicates the sequence of cortical activation during different language and memory tasks. • Linguistic cognitive tasks induce successive activations that precede in both parallel and sequential manners across the cortex. • Identifying specific cortical gyri from structural MRI allows grouping functional activations across several patients to describe a common mode of activation for each task. To describe the spatio-temporal dynamics and interactions during linguistic and memory tasks. Event-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. Transient 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). Between these activations there was widespread spatial divergence followed by convergence of gamma activity that reliably identified cortical areas associated with task-specific processes. The 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. [ABSTRACT FROM AUTHOR]

• Strip electrodes are limited to record electrical-discharges during awake craniotomy. • The 360° electrode array provides a non-inferior temporal-spatial recording dynamic. • After-discharge differentiation may improve our understanding of brain tumor related seizure neurobiology. To evaluate intraoperative use of a novel high-density circular grid in detecting after-discharges (AD) on electrocorticography (ECoG) during functional brain mapping (FBM). FBM during glioma surgery (10/2016 to 5/2019) recorded ADs using a 22-channel circular grid compared to conventional strip electrodes. ADs were analyzed for detection, duration, amplitude, morphology, histology, direction, and clinical signs. Thirty-two patients (mean age 54.2 years; r = 30–75) with glioma (WHO grade II-IV; 20 grade IV) had surgery. ADs during FBM were more likely in patients with wild-type as opposed to IDH-1 mutants (p < 0.0001) using more contacts compared with linear strip electrodes (p = 0.0001). More sensors tended to be involved in ADs detected by the circular grid vs strips (6.61 vs 3.43; p = 0.16) at lower stimulus intensity (3.14 mA vs 4.13 mA; p = 0.09). No difference in the number of cortical stimulations before resection was present (38.9 mA vs 47.9 mA; p = 0.26). ADs longer than 10 seconds were 32.5 seconds (circular grid) vs 58.4 (strips) (p = 0.12). High-density circular grids detect ADs in 360 degrees during FBM for glioma resection. Provocation of ADs was more likely in patients with wild-type than IDH-1 mutation. Circular grids offer high-resolution ECoG during intraoperative FBM for detection of ADs. [ABSTRACT FROM AUTHOR]

• Stability of recorded neural signals is crucial for the clinical viability of implantable brain-computer interfaces (BCIs). • A fully implantable BCI offers a long-term robust and durable control signal in a person with amyotrophic lateral sclerosis. • Increasing home use of the electrocorticography (ECoG)-BCI demonstrates user adoption of the BCI for communication. We investigated the long-term functional stability and home use of a fully implanted electrocorticography (ECoG)-based brain-computer interface (BCI) for communication by an individual with late-stage Amyotrophic Lateral Sclerosis (ALS). Data recorded from the cortical surface of the motor and prefrontal cortex with an implanted brain-computer interface device was evaluated for 36 months after implantation of the system in an individual with late-stage ALS. In addition, electrode impedance and BCI control accuracy were assessed. Key measures included frequency of use of the system for communication, user and system performance, and electrical signal characteristics. User performance was high consistently over the three years. Power in the high frequency band, used for the control signal, declined slowly in the motor cortex, but control over the signal remained unaffected by time. Impedance increased until month 5, and then remained constant. Frequency of home use increased steadily, indicating adoption of the system by the user. The implanted brain-computer interface proves to be robust in an individual with late-stage ALS, given stable performance and control signal for over 36 months. These findings are relevant for the future of implantable brain-computer interfaces along with other brain-sensing technologies, such as responsive neurostimulation. [ABSTRACT FROM AUTHOR]

Highlights • Prospective study evaluating the significance of epileptic activity in ECoGs in children. • Relationship between fast activity recorded in the ECoGs and unfavourable seizure outcomes. • Fast activity recorded with a relatively simple ECoG-equipment might be an alternative to high-frequency oscillations. Abstract Objective To evaluate prospectively the informative/prognostic value of epileptic discharges in the post-resection ECoGs of children with drug-resistant epilepsies and Focal Cortical Dysplasia type II (FCD-II). Methods Included were consecutive patients with focal epilepsies and suspected FCD-II who were planned for single-stage epilepsy surgery based on non-invasive presurgical evaluation results. Intraoperative ECoGs were recorded using a 32-channel system with strip- and/or grid-electrodes. Spikes were defined as transients with a mainly negative component and duration of 20–70 ms. Fast activity was defined as rhythmic bursts of polyspikes >13 Hz. All ECoGs were analysed visually. The significance of both spikes and fast activity in the post-resection ECoG for seizure outcomes 24 months after surgery was evaluated. Results Data from 18 patients (five girls) were analysed. 10/18 patients (55.6%) showed spikes in their post-resection ECoGs, five of them showed additional fast activity. 24 months after surgery, 12/18 patients (66.7%) were seizure-free. There was a significant correlation between unfavorable seizure outcomes and fast activity in the post-resection ECoGs (p = 0.009), whereas spikes alone were not predictive (p = 0.502). Conclusion Even when recorded with non-sophisticated techniques, presence of fast activity in post-resection ECoGs might be a valid negative outcome-predictor after surgery in paediatric patients with FCD-II associated drug-resistant epilepsies. Significance Fast activity recorded with a relatively simple ECoG equipment seems also to have prognostic significance and by this might be an alternative to HFOs recorded with highly sophisticated and expensive technologies. [ABSTRACT FROM AUTHOR]

Highlights • Broadband gamma mapping identified receptive language areas in 22 of 23 subjects. • Comparison with stimulation mapping resulted in 95% sensitivity and 59% specificity. • 82% of contacts identified using broadband gamma were within 1.5 cm of an ECS+ site. Abstract Objective To validate the use of passive functional mapping using electrocorticographic (ECoG) broadband gamma signals for identifying receptive language cortex. Methods We mapped language function in 23 patients using ECoG and using electrical cortical stimulation (ECS) in a subset of 15 subjects. Results The qualitative comparison between cortical sites identified by ECoG and ECS show a high concordance. A quantitative comparison indicates a high level of sensitivity (95%) and a lower level of specificity (59%). Detailed analysis reveals that 82% of all cortical sites identified by ECoG were within one contact of a site identified by ECS. Conclusions These results show that passive functional mapping reliably localizes receptive language areas, and that there is a substantial concordance between the ECoG- and ECS-based methods. They also point to a more refined understanding of the differences between ECoG- and ECS-based mappings. This refined understanding helps to clarify the instances in which the two methods disagree and can explain why neurosurgical practice has established the concept of a "safety margin." Significance Passive functional mapping using ECoG signals provides a fast, robust, and reliable method for identifying receptive language areas without many of the risks and limitations associated with ECS. [ABSTRACT FROM AUTHOR]

Highlights • Extra-operative mapping (penfield technique) frequently leads to after-discharges and seizures. • Intra-operative motor-mapping (IODCS-SDG) using "train of five" provided more mapping information. • No stimulation-provoked seizures were noted during IODCS-SDG. Abstract Objectives The objective of this study was to review our experience with intra-operative "train of five" stimulation using subdural grid for motor mapping in children undergoing epilepsy surgery evaluation. Methods Twenty consecutive children below 18-years of age with drug-refractory epilepsy who underwent invasive-EEG monitoring using subdural-grid placement and intra-operative motor mapping using direct cortical stimulation by sub-dural grid electrodes (IODCS-SDG) at our institution between January-2016 and June-2017 were reviewed. Stimulation was delivered through the subdural-grid electrodes using a train-of-five pulses and muscle responses were recorded by motor-evoked-potentials (MEPs). Intra-operative direct cortical stimulation delivered through a ball-tipped probe (IODCS-probe) and extra-operative motor-mapping (EODCS-SDG) were also performed. Results IODCS-SDG was completed in 20 patients and subsequent EODCS-SDG was done in 17/20 patients. MEP responses were more commonly obtained in the deltoid (19/20), extensor-digitorum-communis (20/20) and first-dorsal-interosseus (19/20). The median thresholds varied between 40 V and 60 V for the six muscle groups. The respective IODCS-probe thresholds tended to be similar. No stimulation-provoked seizures or anaesthesia-related complications were noted during IODCS-SDG. EODCS-SDG could not be completed in 4/17 children and mapping data obtained was frequently inadequate. Nine patients demonstrated 100% concordance between IODCS-SDG and EODCS-SDG for the common mapped body regions. Stimulation-provoked seizures during EODCS-SDG were seen in 6/17 (35.3%) and after-discharges in 7/17 (41.2%) children. Conclusions IODCS-SDG could be performed safely in children with drug refractory epilepsy undergoing invasive EEG monitoring. Significance IODCS-SDG may be a useful adjunct to EODCS-SDG in motor mapping for children. [ABSTRACT FROM AUTHOR]

Highlights • Automated single-pulse electrical stimulation evokes delayed high-frequency suppression (DHFS) in patients with refractory epilepsy. • DHFS serves as a reliable marker of the seizure onset zone (SOZ). • DHFS analysis may increase the speed and reproducibility of SOZ identification. Abstract Objective Single-pulse electrical stimulation (SPES) of intracranial electrodes evokes responses that may help identify the seizure onset zone (SOZ); however, lack of automation and response variability has limited clinical adoption of this technique. We evaluated whether automated delivery of low-current SPES could evoke delayed high-frequency suppression (DHFS) of ongoing electrocorticography (ECoG) signals that, when combined with objective analytic techniques, may provide a reliable marker of this zone. Methods Low-current SPES (1-ms, 3.5-mA biphasic pulses) was delivered to 652 electrodes across 10 patients undergoing ECoG for seizure focus localization. DHFS was measured by calculating the normalized trial-averaged time-frequency power (70–250 Hz) 0.4–1 sec post-stimulation. Electrodes that evoked suppression when stimulated or recorded suppression when stimulation was nearby were used to estimate the SOZ. Results The estimated SOZ significantly identified the clinical SOZ in 6 of 10 patients (5 of 7 temporal foci) with a false-positive rate of 0–0.06. Stimulation required <2 h, was undetectable by patients, and did not induce seizures or after-discharges. Conclusions We show that DHFS provides accurate estimates of the clinical SOZ in patients with refractory epilepsy. Significance This approach may increase the safety, speed, and reproducibility of SOZ identification while reducing cost, subjectivity, and patient discomfort. [ABSTRACT FROM AUTHOR]

Highlights • Automated detection of high-frequency oscillation (HFO) in intraoperative electrocorticography recordings results in a 43% rate of false positive fast ripple detections. • Semi-automated HFO detection that uses visual inspection and annotation editing to remove false positive detections is critical for utilizing HFOs to identify epileptogenic regions. • After semi-automated HFO detection fast ripples on spikes in unresected electrode sites had a high positive predictive value for non-seizure free outcome. Abstract Objective To test the utility of a novel semi-automated method for detecting, validating, and quantifying high-frequency oscillations (HFOs): ripples (80–200 Hz) and fast ripples (200–600 Hz) in intra-operative electrocorticography (ECoG) recordings. Methods Sixteen adult patients with temporal lobe epilepsy (TLE) had intra-operative ECoG recordings at the time of resection. The computer-annotated ECoG recordings were visually inspected and false positive detections were removed. We retrospectively determined the sensitivity, specificity, positive and negative predictive value (PPV/NPV) of HFO detections in unresected regions for determining post-operative seizure outcome. Results Visual validation revealed that 2.81% of ripple and 43.68% of fast ripple detections were false positive. Inter-reader agreement for false positive fast ripple on spike classification was good (ICC = 0.713, 95% CI: 0.632–0.779). After removing false positive detections, the PPV of a single fast ripple on spike in an unresected electrode site for post-operative non-seizure free outcome was 85.7 [50–100%]. Including false positive detections reduced the PPV to 64.2 [57.8–69.83%]. Conclusions Applying automated HFO methods to intraoperative electrocorticography recordings results in false positive fast ripple detections. True fast ripples on spikes are rare, but predict non-seizure free post-operative outcome if found in an unresected site. Significance Semi-automated HFO detection methods are required to accurately identify fast ripple events in intra-operative ECoG recordings. [ABSTRACT FROM AUTHOR]

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). Methods We evaluated 14 epilepsy patients with 1514 subdural electrodes implantation covering the perirolandic cortices at Kyoto University Hospital between 2011 and 2016. We performed multi-component, ECoG-based mapping (band-pass filter, 0.016–300/600 Hz) involving combined analyses of the single components: movement-related cortical potential (<0.5–1 Hz), event-related synchronization (76–200 Hz), and event-related de-synchronization (8–24 Hz) to identify the S1-M1. The feasibility of multi-component mapping was assessed through comparisons with single-component mapping and electrical cortical stimulation (ECS). Results Among 54 functional areas evaluation, ECoG-based maps showed significantly higher rate of localization concordances with ECS maps when the three single-component maps were consistent than when those were inconsistent with each other (p < 0.001 in motor, and p = 0.02 in sensory mappings). Multi-component mapping revealed high sensitivity (89–90%) and specificity (94–97%) as compared with ECS. Conclusions Wide-spectrum, multi-component ECoG-based mapping is feasible, having high sensitivity/specificity relative to ECS. Significance This safe (non-stimulus) mapping strategy, alternative to ECS, would allow clinicians to rule in/out the possibility of brain function prior to resection surgery. [ABSTRACT FROM AUTHOR]

Objective Cortico-cortical evoked potential (CCEP) has been utilized to evaluate connectivity between cortices. However, previous reports have rarely referred to the impact of volume-conducted potential (VCP) which must be a confounding factor of large potential around the stimulation site. To address this issue, we challenged the null hypothesis that VCP accounts for the majority of the recorded potential, particularly around the stimulation site. Methods CCEP was recorded with high-density intracranial electrodes in 8 patients with intractable epilepsy. First, we performed regression analysis for describing the relationship between the distance and potential of each electrode. Second, we performed principal component analysis (PCA) to reveal the temporal features of recorded waveforms. Results The regression curve, declining by the inverse square of the distance, fitted tightly to the plots ( R 2 : 0.878–0.991) with outliers. PCA suggested the responses around the stimulation site had the same temporal features. We also observed the continuous declination over the anatomical gap and the phase reversal phenomena around the stimulation site. Conclusions These results were consistent with the null hypothesis. Significance This study highlighted the risk of misinterpreting CCEP mapping, and proposed mathematical removal of VCP, which could lead to more reliable mapping based on CCEP. [ABSTRACT FROM AUTHOR]

Objective Electrocorticographic (ECoG) mapping of high gamma activity induced by language tasks has been proposed as a more patient friendly alternative for electrocortical stimulation mapping (ESM), the gold standard in pre-surgical language mapping of epilepsy patients. However, ECoG mapping often reveals more language areas than considered critical with ESM. We investigated if critical language areas can be identified with a listening task consisting of speech and music phrases. Methods Nine patients with implanted subdural grid electrodes listened to an audio fragment in which music and speech alternated. We analysed ECoG power in the 65–95 Hz band and obtained task-related activity patterns in electrodes over language areas. We compared the spatial distribution of sites that discriminated between listening to speech and music to ESM results using sensitivity and specificity calculations. Results Our listening task of alternating speech and music phrases had a low sensitivity (0.32) but a high specificity (0.95). Conclusions The high specificity indicates that this test does indeed point to areas that are critical to language processing. Significance Our test cannot replace ESM, but this short and simple task can give a reliable indication where to find critical language areas, better than ECoG mapping using language tasks alone. [ABSTRACT FROM AUTHOR]

Objective: The purpose of this study is to determine the relationship between cortical electrophysiological (CE) signals recorded from the surface of the brain (subdural electrocorticography, or ECoG) and signals recorded extracranially from the subgaleal (SG) space. Methods: We simultaneously recorded several hours of continuous ECoG and SG signals from 3 human pediatric subjects, and compared power spectra of signals between a differential SG montage and several differential ECoG montages to determine the nature of the transfer function between them. Results: We demonstrate the presence of CE signals in the SG montage in the high-gamma range (HG, 70-110 Hz), and the transfer function between 70 and 110 Hz is best characterized as a linear function of frequency. We also test an alternative transfer function, i.e. a single pole filter, to test the hypothesis of frequency dependent attenuation in that range, but find this model to be inferior to the linear model. Conclusions: Our findings indicate that SG electrodes are capable of recording HG signals without frequency distortion compared with ECoG electrodes. Significance: HG signals could be recorded minimally invasively from outside the skull, which could be important for clinical care or brain-computer interface applications. [ABSTRACT FROM AUTHOR]

Objective Human voluntary movements are a final product of complex interactions between multiple sensory, cognitive and motor areas of central nervous system. The objective was to investigate temporal sequence of activation of premotor (PM), primary motor (M1) and somatosensory (S1) areas during cued finger movements. Methods Electrocorticography (ECoG) was used to measure activation timing in human PM, S1, and M1 neurons in preparation for finger movements in 5 subjects with subdural grids for seizure localization. Cortical activation was determined by the onset of high gamma (HG) oscillation (70–150 Hz). The three cortical regions were mapped anatomically using a common brain atlas and confirmed independently with direct electrical cortical stimulation, somatosensory evoked potentials and detection of HG response to tactile stimulation. Subjects were given visual cues to flex each finger or pinch the thumb and index finger. Movements were captured with a dataglove and time-locked with ECoG. A windowed covariance metric was used to identify the rising slope of HG power between two electrodes and compute time lag. Statistical constraints were applied to the time estimates to combat the noise. Rank sum testing was used to verify the sequential activation of cortical regions across 5 subjects. Results In all 5 subjects, HG activation in PM preceded S1 by an average of 53 ± 13 ms ( P = 0.03), PM preceded M1 by 180 ± 40 ms ( P = 0.001) and S1 activation preceded M1 by 136 ± 40 ms ( P = 0.04). Conclusions Sequential HG activation of PM, S1 and M1 regions in preparation for movements is reported. Activity in S1 prior to any overt body movements supports the notion that these neurons may encode sensory information in anticipation of movements, i.e., an efference copy. Our analysis suggests that S1 modulation likely originates from PM. Significance First electrophysiological evidence of efference copy in humans. [ABSTRACT FROM AUTHOR]

Objective Removal of brain tissue showing high frequency oscillations (HFOs; ripples: 80–250 Hz and fast ripples: 250–500 Hz) in preresection electrocorticography (preECoG) in epilepsy patients seems a predictor of good surgical outcome. We analyzed occurrence and localization of HFOs in intra-operative preECoG and postresection electrocorticography (postECoG). Methods HFOs were automatically detected in one-minute epochs of intra-operative ECoG sampled at 2048 Hz of fourteen patients. Ripple, fast ripple, spike, ripples on a spike (RoS) and not on a spike (RnoS) rates were analyzed in pre- and postECoG for resected and nonresected electrodes. Results Ripple, spike and fast ripple rates decreased after resection. RnoS decreased less than RoS (74% vs. 83%; p = 0.01). Most fast ripples in preECoG were located in resected tissue. PostECoG fast ripples occurred in one patient with poor outcome. Patients with good outcome had relatively high postECoG RnoS rates, specifically in the sensorimotor cortex. Conclusions Our observations show that fast ripples in intra-operative ECoG, compared to ripples, may be a better biomarker for epileptogenicity. Further studies have to determine the relation between resection of epileptogenic tissue and physiological ripples generated by the sensorimotor cortex. Significance Fast ripples in intra-operative ECoG can help identify the epileptogenic zone, while ripples might also be physiological. [ABSTRACT FROM AUTHOR]

Objective We investigated the relationship between locations of broadband peri-ictal electrocorticographic activities determined by a semi-automatic detection method and seizure onset zones in medically intractable epilepsy patients. Methods We included 18 patients. Peri-ictal periods (−15 to +5 s from the ictal onset) were divided into 4 periods of 5 s duration each in bandwidth from 1 to 700 Hz divided into 11 bins. Thereafter, we calculated the mean overlapping percentage of the maximum amplitude activity electrodes with the seizure onset zone in the total number of seizures in each patient. Significance was considered at an adjusted p -value of 0.05. Results By the maximum amplitude method with the Bonferroni correction, only high-frequency activities (>60 Hz) during −5 to 0 s from the ictal onset were significantly related to seizure onset zones. In post hoc analyses, bands in 60–139 Hz and 4–7 Hz were significantly related to seizure onset zones in the Bonferroni correction. However, after the less conservative Benjamini–Yekutieli correction and with the epileptogenicity index, other bands and periods after −10 s from the ictal onset were also related with seizure onset zones. Significance Detailed bands, timings and analytic methods of peri-ictal activities with high relationships to seizure onset zones were identified. [ABSTRACT FROM AUTHOR]