Subdural Electrodes Research Articles

The Brain is Not Flat: Conformal Electrode Arrays Diminish Complications of Subdural Electrode Implantation, A Series of 117 Cases

Intracranial recordings are integral to evaluating patients with pharmacoresistant epilepsy whom noninvasive testing fails to localize seizure focus. Although stereo-electroencephalography is the preferred method of intracranial recordings in most centers, subdural electrode (SDE) implantation is necessary in selected cases. To identify imaging correlates that predict SDE complications (extra-axial fluid collections [EFCs]), and determine if modifications that diminish stiffness of electrode sheets reduce complications. A prospective epilepsy surgery database was used to identify adults undergoing craniotomy for SDE implantation over a 14-year period. EFCs and midline shift were measured via magnetic resonance imaging and computed tomography imaging. Correlation analyses and multivariable logistic regression explored associations between use of conformal arrays, serial order of patients, previous ipsilateral intracranial surgery, midline shift, number of SDEs, and neurologic complications. A total of 111 consecutive patients (59 female) underwent 117 craniotomies (mean, 115 electrode contacts) for SDE implantation. There were 8 surgical complications, 3 in the first 17 (17.7%). and 5 (after electrode modifications) in a subsequent 100 craniotomies (5.0%). We noted an increase in electrode numbers implanted over time (P < 0.001) and decreased midline shift with conformal grids (ρ= - 0.32; P < 0.001). A multivariable regression showed that midline shift correlated with complications (odds ratio, 2.32; 95% confidence interval, 1.12-4.78; P= 0.023). Hemorrhagic complications after SDE implantation are difficult to detect because of artifact from electrodes, but predictable by prominent midline shift (>4 mm). Risks inherent to SDE implantation may be minimized using conformal grids. With symptomatic EFCs, a single electrode cable exit site allows hematoma evacuation without terminating intracranial recordings.

Prediction of seizure freedom after epilepsy surgery – Critical reappraisal of significance of intracranial EEG parameters

ObjectiveTo analyze the significance of intracranial electroencephalography (iEEG) parameters such as seizure onset patterns (SOP) and size of seizure onset zone (SOZ) with respect to prediction of seizure freedom after resective epilepsy surgery. MethodsAll patients who underwent iEEG with subdural electrodes between January 2006 and December 2015 in our epilepsy-center were included. Various iEEG parameters were retrospectively analyzed regarding their predictive value to post-operative seizure freedom. Furthermore, associations of specific SOPs with underlying histopathology and brain regions of the SOZ were examined. ResultsEighty-one patients (34 female) with 324 seizures were assessed. Low-voltage fast activity (37%) and sharp activity <13 Hz (30%) were the most frequent SOPs. Focal SOZ (≤2 cm) was the only iEEG parameter independently associated with 1-year post-operative seizure freedom (OR 4.1, 95% CI 1.433–11.679). While no SOP was linked to specific histopathologies, some associations between SOPs and anatomical regions of SOZ were found. ConclusionsA circumscribed SOZ, but no specific SOP was predictive for seizure freedom after epilepsy surgery. SignificanceIntracranial EEG may be helpful to predict post-operative seizure freedom. Multicenter studies with larger numbers of patients are required to reliably assess the significance of specific SOPs for successful resective epilepsy surgery.

Electrocorticography in patients with severe traumatic brain injury

Introduction. The frequency of adverse outcomes in patients with severe traumatic brain injury (TBI) exceeds 25%. Epileptic seizures and vasospasm, in the absence of pathogenetic treatment, cause irreversible brain damage and thus complicate the course of severe TBI. Bedside electroencephalography (EEG) is traditionally used to diagnose these conditions. However, its low spatial resolution when recording from the scalp and a large number of artefacts that make it challenging to analyse the data. Materials and methods. Electrocorticography (ECoG) monitoring was performed using subdural electrodes implanted in the traumatic brain lesion during TBI surgery in 11 patients during the acute period of severe TBI. All patients were concurrently monitored using scalp EEG with subdermal needle electrodes. Results. Analysis of scalp recordings showed frequency disturbances and oscillation asymmetry in all patients, while sporadic epileptiform activity and rhythmic and periodic patterns were detected in 18% and 64% of subjects, respectively. Analysis of invasive EEG showed sporadic epileptiform activity in 27% of patients, while rhythmic and periodic patterns were present in 91%. Moreover, epileptiform activity was registered only by the subdural leads in 3 patients. The total percentage of subjects in whom we registered clinical and electrographic signs of convulsive and non-convulsive status epilepticus using EEG and ECoG was 55%. We found indirect EEG signs of slow-spreading cortical depolarization in one patient whose level of consciousness was coma, followed by an electrographic pattern of status epilepticus on ECoG. Conclusion. ECoG recording, while patients with severe TBI are in the intensive care unit, increases the diagnostic capabilities of this method, allowing electrographic seizures to be recorded more often and more accurately, but also to detect indirect signs of slow-spreading cortical depolarization using standard EEG amplifiers. Electrode implantation during TBI surgery is safe and does not significantly change the surgical approach.

Localization of deep brain activity with scalp and subdural EEG

To what extent electrocorticography (ECoG) and electroencephalography (scalp EEG) differ in their capability to locate sources of deep brain activity is far from evident. Compared to EEG, the spatial resolution and signal-to-noise ratio of ECoG is superior but its spatial coverage is more restricted, as is arguably the volume of tissue activity effectively measured from. Moreover, scalp EEG studies are providing evidence of locating activity from deep sources such as the hippocampus using high-density setups during quiet wakefulness. To address this question, we recorded a multimodal dataset from 4 patients with refractory epilepsy during quiet wakefulness. This data comprises simultaneous scalp, subdural and depth EEG electrode recordings. The latter was located in the hippocampus or insula and provided us with our “ground truth” for source localization of deep activity. We applied independent component analysis (ICA) for the purpose of separating the independent sources in theta, alpha and beta frequency band activity. In all patients subdural- and scalp EEG components were observed which had a significant zero-lag correlation with one or more contacts of the depth electrodes. Subsequent dipole modeling of the correlating components revealed dipole locations that were significantly closer to the depth electrodes compared to the dipole location of non-correlating components. These findings support the idea that components found in both recording modalities originate from neural activity in close proximity to the depth electrodes. Sources localized with subdural electrodes were ~70% closer to the depth electrode than sources localized with EEG with an absolute improvement of around ~2cm. In our opinion, this is not a considerable improvement in source localization accuracy given that, for clinical purposes, ECoG electrodes were implanted in close proximity to the depth electrodes. Furthermore, the ECoG grid attenuates the scalp EEG, due to the electrically isolating silastic sheets in which the ECoG electrodes are embedded. Our results on dipole modeling show that the deep source localization accuracy of scalp EEG is comparable to that of ECoG. Significance StatementDeep and subcortical regions play an important role in brain function. However, as joint recordings at multiple spatial scales to study brain function in humans are still scarce, it is still unresolved to what extent ECoG and EEG differ in their capability to locate sources of deep brain activity. To the best of our knowledge, this is the first study presenting a dataset of simultaneously recorded EEG, ECoG and depth electrodes in the hippocampus or insula, with a focus on non-epileptiform activity (quiet wakefulness). Furthermore, we are the first study to provide experimental findings on the comparison of source localization of deep cortical structures between invasive and non-invasive brain activity measured from the cortical surface.

Factors influencing the long-term prognosis of patients with temporal lobe epilepsy: a single center study.

This study aimed to explore the risk factors influencing the long-term prognosis of temporal lobe epilepsy (TLE) patients treated with drug therapy or surgical treatment. A total of 112 patients who were diagnosed with TLE were retrospectively enrolled. All of the patients were initially treated with antiepileptic drugs (AEDs). Patients who met the criteria of drugresistant TLE were evaluated for treatment with temporal lobectomy. The main outcome was whether the patients achieved seizure-free status. This was defined as when a patient experienced no seizures for at least 24 months of follow-up. The independent predictors of the outcome were evaluated using a multiple logistic regression model. The median follow-up period was 5 years (range, 2-13 years). At the end of follow-up, 26 patients had not achieved seizure freedom after treatment with AEDs, including 22 cases of monotherapy, 4 cases of duotherapy (1 case of drug-resistant epilepsy after continuous drug treatment). AED treatment was withdrawn in 6 patients. Overall, 23.2% TLE patients (26/112) achieved seizure freedom after treatment with AEDs alone, while the remaining 76.8% (86/112) of patients were diagnosed as drug-resistant epilepsy (DRE). Of the 45 DRE patients who subsequently received surgical treatment, 77.8% (35/45) achieved seizure freedom, with successful AED withdrawal in 11 patients. The proportion of patients who achieved seizure-free status was higher among those who underwent temporal lobectomy than among those who continued with AED treatment (77.8% vs. 23.2%, P<0.001). Effective early monotherapy was an independent predictor for good therapeutic effect in all TLE patients (OR: 0.16; 95% CI: 0.04-0.66; P=0.007). Multivariate logistic regression analysis showed the predictors of good prognosis in DRE patients after surgery to be unilateral origin of discharges in electroencephalogram (EEG, OR =0.20, 95% CI: 0.06-0.74, P=0.016), no secondary generalized tonic-clonic seizures (GTCS, OR =0.08, 95% CI: 0.01-0.67, P=0.002), and not needing a subdural electrode (OR =15.4, 95% CI: 1.36-174.38, P=0.027). Effective early monotherapy was an independent protective factor for the favorable prognosis of TLE. Unilateral origin of discharges in EEG, no secondary GTCS, and not needing a subdural electrode were independent factors associated with favorable prognosis after TLE surgery.

Direct brain recordings identify hippocampal and cortical networks that distinguish successful versus failed episodic memory retrieval

Human data collected using noninvasive imaging techniques have established the importance of parietal regions towards episodic memory retrieval, including the angular gyrus and posterior cingulate cortex. Such regions comprise part of a putative core episodic retrieval network. In free recall, comparisons between contextually appropriate and inappropriate recall events (i.e. prior list intrusions) provide the opportunity to study memory retrieval networks supporting veridical recall, and existing findings predict that differences in electrical activity in these brain regions should be identified according to the accuracy of recall. However, prior iEEG studies, utilizing principally subdural grid electrodes, have not fully characterized brain activity in parietal regions during memory retrieval and have not examined connectivity between core recollection areas and the hippocampus or prefrontal cortex. Here, we employed a data set obtained from 100 human patients implanted with stereo EEG electrodes for seizure mapping purposes as they performed a free recall task. This data set allowed us to separately analyze activity in midline versus lateral parietal brain regions, and in anterior versus posterior hippocampus, to identify areas in which retrieval-related activity predicted the recollection of a correct versus an incorrect memory. With the wide coverage afforded by the stereo EEG approach, we were also able to examine interregional connectivity. Our key findings were that differences in gamma band activity in the angular gyrus, precuneus, posterior temporal cortex, and posterior (more than anterior) hippocampus discriminated accurate versus inaccurate recall as well as active retrieval versus memory search. The left angular gyrus exhibited a significant power decrease preceding list intrusions as well as unique phase–amplitude coupling properties, whereas the prefrontal cortex was unique in exhibiting a power increase during list intrusions. Analysis of connectivity revealed significant hemispheric asymmetry, with relatively sparse left-sided functional connections compared to the right hemisphere. One exception to this finding was elevated connectivity between the prefrontal cortex and left angular gyrus. This finding is interpreted as evidence for the engagement of prefrontal cortex in memory monitoring and mnemonic decision-making.

Totally transparent hydrogel-based subdural electrode with patterned salt bridge.

A totally transparent subdural electrode was developed by embedding a conductive poly (vinyl alcohol) (PVA)-filled microchannel made of poly(dimethylsiloxane) (PDMS) into an another PVA hydrogel substrate. Tight bonding between the PVA substrate and the PDMS microchannel (salt bridge) was achieved by mechanical interlocking utilizing the microprotrusions formed on the microchannel. This simple method of bonding without the use of any additives such as silane molecules or nanofibers is very suitable for constructing biomedical devices. The salt bridge electrode (total thickness, ca. 1.5mm) was sufficiently soft, and showed superior shape conformability that makes it an excellent choice as a subdural electrode used on the brain surface. In vivo measurement proved that the salt bridge electrode makes close contact to the exposed porcine brain and can record brain wave signals of frequencies 1 ~ 15Hz. In addition, the high transparency of the electrode provided a clear view of the brain surface that would assist the effective surgical operation and optogenetic research.

Cross-national disparities contribute to heterogeneity in patient outcomes following invasive monitoring: A hierarchical mixed-effects analysis.

There is substantial variability in outcomes following invasive monitoring and surgical treatment of drug-resistant epilepsy (DRE). Patients with DRE are uniquely vulnerable to cross-national health care disparities, as their epilepsy is difficult to treat and requires extensive resources. In a large cross-national database of patients undergoing invasive monitoring for epilepsy surgery, we sought to evaluate the association between social, economic, and educational indicators of the country of treatment and patient outcomes following invasive monitoring. We performed a mixed-effects analysis of an individual patient database of 595 subjects enrolled in 33 studies encompassing 25 neurosurgical centers in 10 countries of invasive monitoring for epilepsy from 1996 to 2019. Upon preliminary univariate analysis, significant nation-level predictors of seizure outcome following either stereoelectroencephalography or subdural electrodes were hospital beds per 100,000 population, physician density, gross domestic product (GDP) growth, male and female educational attainment, and unemployment rate. On multivariate mixed-effects logistic regression, physician density (β=-0.5112, P<.00697) and GDP growth (β=0.53822, P<.00404) were the only nation-level covariates of significance associated with seizure outcome. A higher physician density was associated with lesser seizure freedom rates, whereas higher GDP growth was associated with greater seizure freedom rates. Although patient-specific variables were the primary determinant of seizure outcomes, cross-national disparities also contribute to heterogeneities. Our findings highlight the importance of a systems-level dialogue to improve surgical outcomes for DRE patients.

RTTBD-like activity in association with hippocampal ictal discharges in patients with temporal lobe epilepsy.

To determine clinical and intracranial EEG correlates of rhythmic temporal theta bursts of drowsiness (RTTBD) and assess its clinical significance in patients with temporal lobe epilepsy (TLE). A retrospective review of simultaneous scalp and intracranial video-EEG recordings from 28 patients with TLE was evaluated for epilepsy surgery. Scalp RTTBD patterns were identified and their clinical and intracranial EEG correlates were then determined on video-EEG recording using depth and subdural electrodes. Thirty-one RTTBD patterns on scalp EEG were observed in six (21%) of the 28 patients. Five (16%) of the RTTBD patterns occurred during wakefulness and 26 (84%) occurred during drowsiness and light sleep. The mean duration of RTTBD was 10 seconds (range: 3-28seconds). RTTDB consistently correlated with hippocampal ictal discharges and was time-locked to the hippocampal seizures in which the ictal discharges evolved into rhythmic theta frequency (4-7-Hz) range. Ictal automatisms were observed during five (16%) RTTBD patterns, while cognitive impairment was observed in four (13%) of the 31 RTTBD patterns. Our findings show that scalp EEG correlates of hippocampal ictal discharges can resemble RTTBD and may be associated with ictal symptoms and cognitive impairment, indicating that RTTBD may rarely be an ictal EEG pattern in patients with TLE.

Fabrication and validation of reference structures for the localization of subdural standard- and micro-electrodes in MRI

Objective. Report simple reference structure fabrication and validate the precise localization of subdural micro- and standard electrodes in magnetic resonance imaging (MRI) in phantom experiments. Approach. Electrode contacts with diameters of 0.3 mm and 4 mm are localized in 1.5 T MRI using reference structures made of silicone and iron oxide nanoparticle doping. The precision of the localization procedure was assessed for several standard MRI sequences and implant orientations in phantom experiments and compared to common clinical localization procedures. Main results. A localization precision of 0.41 ± 0.20 mm could be achieved for both electrode diameters compared to 1.46 ± 0.69 mm that was achieved for 4 mm standard electrode contacts localized using a common clinical standard method. The new reference structures are intrinsically bio-compatible, and they can be detected with currently available feature detection software so that a clinical implementation of this technology should be feasible. Significance. Neuropathologies are increasingly diagnosed and treated with subdural electrodes, where the exact localization of the electrode contacts with respect to the patient’s cortical anatomy is a prerequisite for the procedure. Post-implantation electrode localization using MRI may be advantageous compared to the common alternative of CT-MRI image co-registration, as it avoids systematic localization errors associated with the co-registration itself, as well as brain shift and implant movement. Additionally, MRI provides superior soft tissue contrast for the identification of brain lesions without exposing the patient to ionizing radiation. Recent studies show that smaller electrodes and high-density electrode grids are ideal for clinical and research purposes, but the localization of these devices in MRI has not been demonstrated.

Intracranial EEG in the 21st Century

Intracranial electroencephalography (iEEG) has been the mainstay of identifying the seizure onset zone (SOZ), a key diagnostic procedure in addition to neuroimaging when considering epilepsy surgery. In many patients, iEEG has been the basis for resective epilepsy surgery, to date still the most successful treatment for drug-resistant epilepsy. Intracranial EEG determines the location and resectability of the SOZ. Advances in recording and implantation of iEEG provide multiple options in the 21st century. This not only includes the choice between subdural electrodes (SDE) and stereoelectroencephalography (SEEG) but also includes the implantation and recordings from microelectrodes. Before iEEG implantation, especially in magnetic resonance imaging -negative epilepsy, a clear hypothesis for seizure generation and propagation should be based on noninvasive methods. Intracranial EEG implantation should be planned by a multidisciplinary team considering epileptic networks. Recordings from SDE and SEEG have both their advantages and disadvantages. Stereo-EEG seems to have a lower rate of complications that are clinically significant, but has limitations in spatial sampling of the cortical surface. Stereo-EEG can sample deeper areas of the brain including deep sulci and hard to reach areas such as the insula. To determine the epileptogenic zone, interictal and ictal information should be taken into consideration. Interictal spiking, low frequency slowing, as well as high frequency oscillations may inform about the epileptogenic zone. Ictally, high frequency onsets in the beta/gamma range are usually associated with the SOZ, but specialized recordings with combined macro and microelectrodes may in the future educate us about onset in higher frequency bands. Stimulation of intracranial electrodes triggering habitual seizures can assist in identifying the SOZ. Advanced computational methods such as determining the epileptogenicity index and similar measures may enhance standard clinical interpretation. Improved techniques to record and interpret iEEG may in the future lead to a greater proportion of patients being seizure free after epilepsy surgery.

A systematic review of endovascular stent-electrode arrays, a minimally invasive approach to brain-machine interfaces.

The goal of this study was to systematically review the feasibility and safety of minimally invasive neurovascular approaches to brain-machine interfaces (BMIs). A systematic literature review was performed using the PubMed database for studies published between 1986 and 2019. All studies assessing endovascular neural interfaces were included. Additional studies were selected based on review of references of selected articles and review articles. Of the 53 total articles identified in the original literature search, 12 studies were ultimately selected. An additional 10 articles were included from other sources, resulting in a total of 22 studies included in this systematic review. This includes primarily preclinical studies comparing endovascular electrode recordings with subdural and epidural electrodes, as well as studies evaluating stent-electrode gauge and material type. In addition, several clinical studies are also included. Endovascular stent-electrode arrays provide a minimally invasive approach to BMIs. Stent-electrode placement has been shown to be both efficacious and safe, although further data are necessary to draw comparisons between subdural and epidural electrode measurements given the heterogeneity of the studies included. Greater access to deep-seated brain regions is now more feasible with stent-electrode arrays; however, further validation is needed in large clinical trials to optimize this neural interface. This includes the determination of ideal electrode material type, venous versus arterial approaches, the feasibility of deep brain stimulation, and more streamlined computational decoding techniques.

Stable high frequency background EEG activity distinguishes epileptic from healthy brain regions.

High-frequency oscillations are markers of epileptic tissue. Recently, different patterns of EEG background activity were described from which high-frequency oscillations occur: high-frequency oscillations with continuously oscillating background were found to be primarily physiological, those from quiet background were linked to epileptic tissue. It is unclear, whether these interactions remain stable over several days and during different sleep-wake stages. High-frequency oscillation patterns (oscillatory vs. quiet background) were analysed in 23 patients implanted with depth and subdural grid electrodes. Pattern scoring was performed on every channel in 10 s intervals in three separate day- and night-time EEG segments. An entropy value, measuring variability of patterns per channel, was calculated. A low entropy value indicated a stable occurrence of the same pattern in one channel, whereas a high value indicated pattern instability. Differences in pattern distribution and entropy were analysed for 143 280 10 s intervals with allocated patterns from inside and outside the seizure onset zone, different electrode types and brain regions. We found a strong association between high-frequency oscillations out of quiet background activity, and channels of the seizure onset zone (35.2% inside versus 9.7% outside the seizure onset zone, P < 0.001), no association was found for high-frequency oscillations from continuous oscillatory background (P = 0.563). The type of background activity remained stable over the same brain region over several days and was independent of sleep stage and recording technique. Stability of background activity was significantly higher in channels of the seizure onset zone (entropy mean value 0.56 ± 0.39 versus 0.64 ± 0.41; P < 0.001). This was especially true for the presumed epileptic high-frequency oscillations out of quiet background (0.57 ± 0.39 inside versus 0.72 ± 0.37 outside the seizure onset zone; P < 0.001). In contrast, presumed physiological high-frequency oscillations from continuous oscillatory backgrounds were significantly more stable outside the seizure onset zone (0.72 ± 0.45 versus 0.48 ± 0.53; P < 0.001). The overall low entropy values suggest that interactions between high-frequency oscillations and background activity are a stable phenomenon specific to the function of brain regions. High-frequency oscillations occurring from a quiet background are strongly linked to the seizure onset zone whereas high-frequency oscillations from an oscillatory background are not. Pattern stability suggests distinct underlying mechanisms. Analysing short time segments of high-frequency oscillations and background activity could help distinguishing epileptic from physiologically active brain regions.

Stereoelectroencephalography Versus Subdural Strip Electrode Implantations: Feasibility, Complications, and Outcomes in 500 Intracranial Monitoring Cases for Drug-Resistant Epilepsy.

Both stereoelectroencephalography (SEEG) and subdural strip electrodes (SSE) are used for intracranial electroencephalographic recordings in the invasive investigation of patients with drug-resistant epilepsy. To compare SEEG and SSE with respect to feasibility, complications, and outcome in this single-center study. Patient characteristics, periprocedural parameters, complications, and outcome were acquired from a pro- and retrospectively managed databank to compare SEEG and SSE cases. A total of 500 intracranial electroencephalographic monitoring cases in 450 patients were analyzed (145 SEEG and 355 SSE). Both groups were of similar age, gender distribution, and duration of epilepsy. Implantation of each SEEG electrode took 13.9± 7.6 min (20±12 min for each SSE; P<.01). Radiation exposure to the patient was 4.3±7.7 s to a dose area product of 14.6±27.9 rad*cm2 for SEEG and 9.4±8.9 s with 21±22.4 rad*cm2 for SSE (P<.01). There was no difference in the length of stay (12.2±7.2 and 12±6.3 d). The complication rate was low in both groups. No infections were seen in SEEG cases (2.3% after SSE). The rate of hemorrhage was 2.8% for SEEG and 1.4% for SSE. Surgical outcome was similar. SEEG allows targeting deeply situated foci with a non-inferior safety profile to SSE and seizure outcome comparable to SSE.

Engagement of cortico-cortical and cortico-subcortical networks in a patient with epileptic spasms: An integrated neurophysiological study

ObjectiveWe aimed to delineate the engagement of cortico-cortical and cortico-subcortical networks in the generation of epileptic spasms (ES) using integrated neurophysiological techniques. MethodsSeventeen-year-old male patient with intractable ES underwent chronic subdural electrode implantation for presurgical evaluation. Networks were evaluated in ictal periods using high-frequency oscillation (HFO) analysis and in interictal periods using magnetoencephalography (MEG) and simultaneous electroencephalography, and functional magnetic resonance imaging (EEG-fMRI). Cortico-cortical evoked potentials (CCEPs) were recorded to trace connections among the networks. ResultsIctal HFO revealed a network comprising multilobar cortical regions (frontal, parietal, and temporal), but sparing the positive motor area. Interictally, MEG and EEG-fMRI revealed spike-and-wave-related activation in these cortical regions. Analysis of CCEPs provided evidence of connectivity within the cortico-cortical network. Additionally, EEG-fMRI results indicate the involvement of subcortical structures, such as bilateral thalamus (predominantly right) and midbrain. ConclusionsIn this case study, integrated neurophysiological techniques provided converging evidence for the involvement of a cortico-cortical network (sparing the positive motor area) and a cortico-subcortical network in the generation of ES in the patient. SignificanceCortico-cortical and cortico-subcortical pathways, with the exception of the direct descending corticospinal pathway from the positive motor area, may play important roles in the generation of ES.

Neural decoding of electrocorticographic signals using dynamic mode decomposition

Objective. Brain-computer interfaces (BCIs) using electrocorticographic (ECoG) signals have been developed to restore the communication function of severely paralyzed patients. However, the limited amount of information derived from ECoG signals hinders their clinical applications. We aimed to develop a method to decode ECoG signals using spatiotemporal patterns characterizing movement types to increase the amount of information gained from these signals. Approach. Previous studies have demonstrated that motor information could be decoded using powers of specific frequency bands of the ECoG signals estimated by fast Fourier transform (FFT) or wavelet analysis. However, because FFT is evaluated for each channel, the temporal and spatial patterns among channels are difficult to evaluate. Here, we used dynamic mode decomposition (DMD) to evaluate the spatiotemporal pattern of ECoG signals and evaluated the accuracy of motor decoding with the DMD modes. We used ECoG signals during three types of hand movements, which were recorded from 11 patients implanted with subdural electrodes. From the signals at the time of the movements, the modes and powers were evaluated by DMD and FFT and were decoded using support vector machine. We used the Grassmann kernel to evaluate the distance between modes estimated by DMD (DMD mode). In addition, we decoded the DMD modes, in which the phase components were shuffled, to compare the classification accuracy. Main results. The decoding accuracy using DMD modes was significantly better than that using FFT powers. The accuracy significantly decreased when the phases of the DMD mode were shuffled. Among the frequency bands, the DMD mode at approximately 100 Hz demonstrated the highest classification accuracy. Significance. DMD successfully captured the spatiotemporal patterns characterizing the movement types and contributed to improving the decoding accuracy. This method can be applied to improve BCIs to help severely paralyzed patients communicate.

Electrocorticographic and neurochemical findings after local cortical valproate application in patients with pharmacoresistant focal epilepsy.

Because oral pharmacological treatment of neocortical focal epilepsy is limited due to common systemic side effects and relatively low drug concentrations reached at the epileptic foci locally, application of antiepileptic agents directly onto the neocortical focus may enhance treatment tolerability and efficacy. We describe the effects of cortically applied sodium valproate (VPA) in two patients with pharmacoresistant neocortical focal epilepsy who were selected for epilepsy surgery after a circumscribed epileptic focus had been determined by invasive presurgical evaluation using subdural electrodes. Local VPA modified epileptic activity as electrocorticographically recorded from the chronic focus in both patients. In addition, VPA induced local increase of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) in cortical tissue samples, whereas the excitatory glutamate was possibly decreased. In this clinical pilot study, we could show antiepileptic effects of cortically applied VPA in humans by electrocorticographic and neurochemical parameters.

Spreading depolarization may represent a novel mechanism for delayed fluctuating neurological deficit after chronic subdural hematoma evacuation.

Most patients with chronic subdural hematoma (cSDH) recover after surgical evacuation with a straightforward course. There is a subset of patients who develop transient and fluctuating deficits not explained by seizures, stroke, or mass effect after evacuation. The objective of this study was to investigate whether these postoperative neurological deficits may be related to temporary brain dysfunction caused by cortical spreading depolarizations (SDs). The authors conducted a prospective observational study of 40 patients who underwent cSDH evacuation. At the time of surgery, a 1 × 6 subdural electrode strip was placed on the cortex parallel to the subdural drain. Clinical outcomes were assessed utilizing the Markwalder Grading Scale, need for clinical EEG for new deficit, and presence of new deficits. Definitive SD was detected in 6 (15%) of 40 patients. Baseline and cSDH characteristics did not differ between patients with and without SD. More patients experienced postoperative neurological deterioration if they had SD (50%) compared to those without SD (8.8%; p = 0.03). Only 2 patients in the entire cohort demonstrated early neurological deterioration, both of whom had SD. One of these cases demonstrated a time-locked new focal neurological deficit (aphasia) at the start of a series of multiple clusters of SD. This is the first observation of SD occurring after cSDH evacuation. SD occurred at a rate of 15% and was associated with neurological deterioration. This may represent a novel mechanism for otherwise unexplained fluctuating neurological deficit after cSDH evacuation. This could provide a new therapeutic target, and SD-targeted therapies should be evaluated in prospective clinical trials.

Differentiating tic electrophysiology from voluntary movement in the human thalamocortical circuit

ObjectivesTourette syndrome is a neurodevelopmental disorder commonly associated with involuntary movements, or tics. We currently lack an ideal animal model for Tourette syndrome. In humans, clinical manifestation of tics cannot...

Seizure Freedom in Temporal Plus Epilepsy Surgery Following Stereo-Electroencephalography.

"Temporal plus" epilepsy (TPE) is a term that is used when the epileptogenic zone (EZ) extends beyond the boundaries of the temporal lobe. Stereotactic electroencephalography (SEEG) has been essential to identify additional EZs in adjacent structures that might be part of the temporal lobe/limbic network. We present a small case series of temporal plus cases successfully identified by SEEG who were seizure-free after resective surgery. We conducted a retrospective analysis of 156 patients who underwent SEEG in 5 years. Six cases had TPE and underwent anterior temporal lobectomy (ATL) with additional extra-temporal resections. Five cases had a focus on the right hemisphere and one on the left. Three cases were non-lesional and three were lesional. Mean follow-up time since surgery was 2.9 years (SD ± 1.8). Three patients had subdural electrodes investigation prior or in addition to SEEG. All patients underwent standard ATL and additional extra-temporal resections during the same procedure or at a later date. All patients were seizure-free at their last follow-up appointment (Engel Ia = 3; Engel Ib = 2; Engel Ic = 1). Pathology was nonspecific/gliosis for all six cases. TPE might explain some of the failures in temporal lobe epilepsy surgery. We present a small case series of six patients in whom SEEG successfully identified this phenomenon and surgery proved effective.