Theta Oscillations Support Prefrontal-hippocampal Interactions in Sequential Working Memory

The prefrontal cortex and hippocampus may support sequential working memory beyond episodic memory and spatial navigation. This stereoelectroencephalography (SEEG) study investigated how the dorsolateral prefrontal cortex (DLPFC) interacts with the hippocampus in the online processing of sequential information. Twenty patients with epilepsy (eight women, age 27.6 ± 8.2 years) completed a line ordering task with SEEG recordings over the DLPFC and the hippocampus. Participants showed longer thinking times and more recall errors when asked to arrange random lines clockwise (random trials) than to maintain ordered lines (ordered trials) before recalling the orientation of a particular line. First, the ordering-related increase in thinking time and recall error was associated with a transient theta power increase in the hippocampus and a sustained theta power increase in the DLPFC (3-10 Hz). In particular, the hippocampal theta power increase correlated with the memory precision of line orientation. Second, theta phase coherences between the DLPFC and hippocampus were enhanced for ordering, especially for more precisely memorized lines. Third, the theta band DLPFC → hippocampus influence was selectively enhanced for ordering, especially for more precisely memorized lines. This study suggests that theta oscillations may support DLPFC-hippocampal interactions in the online processing of sequential information.

A method for chronic and semi-chronic microelectrode array implantation in deep brain structures using image guided neuronavigation

BACKGROUND

Accurate targeting of brain structures for in-vivo electrophysiological recordings is essential for basic as well as clinical neuroscience research. Although methodologies for precise targeting and recording from the cortical surface are abundant, such protocols are scarce for deep brain structures.

NEW METHOD

We have incorporated stable fiducial markers within a custom cranial cap for improved image-guided neuronavigation targeting of subcortical structures in macaque monkeys. Anchor bolt chambers allowed for a minimally invasive entrance into the brain for chronic recordings. A 3D-printed microdrive allowed for semi-chronic applications.

RESULTS

We achieved an average Euclidean targeting error of 1.6 mm and a radial error of 1.2 mm over three implantations in two animals. Chronic and semi-chronic implantations allowed for recording of extracellular neuronal activity, with single-neuron activity examples shown from one macaque monkey.

COMPARISON WITH EXISTING METHOD(S)

Traditional stereotactic methods ignore individual anatomical variability. Our targeting approach allows for a flexible, subject-specific surgical plan with targeting errors lower than what is reported in humans, and equal to or lower than animal models using similar methods. Utilizing an anchor bolt as a chamber reduced the craniotomy size needed for electrode implantation, compared to conventional large access chambers which are prone to infection. Installation of an in-house, 3D-printed, screw-to-mount mechanical microdrive is in contrast to existing semi-chronic methods requiring fabrication, assembly, and installation of complex parts.

CONCLUSIONS

Leveraging commercially available tools for implantation, our protocol decreases the risk of infection from open craniotomies, and improves the accuracy of chronic electrode implantations targeting deep brain structures in large animal models.

Variability of Single Pulse Electrical Stimulation Responses Recorded with Intracranial Electroencephalography in Epileptic Patients

Cohort studies of brain stimulations performed with stereo-electroencephalographic (SEEG) electrodes in epileptic patients allow to derive large scale functional connectivity. It is known, however, that brain responses to electrical or magnetic stimulation techniques are not always reproducible. Here, we study variability of responses to single pulse SEEG electrical stimulation. We introduce a second-order probability analysis, i.e. we extend estimation of connection probabilities, defined as the proportion of responses trespassing a statistical threshold (determined in terms of Z-score with respect to spontaneous neuronal activity before stimulation) over all responses and derived from a number of individual measurements, to an analysis of pairs of measurements.Data from 445 patients were processed. We found that variability between two equivalent measurements is substantial in particular conditions. For long ( > ~ 90 mm) distances between stimulating and recording sites, and threshold value Z = 3, correlation between measurements drops almost to zero. In general, it remains below 0.5 when the threshold is smaller than Z = 4 or the stimulating current intensity is 1 mA. It grows with an increase of either of these factors. Variability is independent of interictal spiking rates in the stimulating and recording sites.We conclude that responses to SEEG stimulation in the human brain are variable, i.e. in a subject at rest, two stimulation trains performed at the same electrode contacts and with the same protocol can give discrepant results. Our findings highlight an advantage of probabilistic interpretation of such results even in the context of a single individual.

Drug-resistant temporal lobe epilepsy due to middle fossa meningoencephalocele in a child: A surgical case report

BACKGROUND

Meningoencephalocele (ME) of the temporal lobe through a bone defect in the middle cranial fossa is a rare known cause of refractory temporal lobe epilepsy (TLE). ME-induced drug-resistant TLE has been described in adults; however, its incidence in children is very rare.

CASE REPORT

A 7-year-old girl presented at our hospital with brief episodes of impaired consciousness and enuresis. Initial brain MRI results were interpreted as normal. Her seizures could not be controlled even with multiple anti-seizure medications. She was diagnosed with drug-resistant TLE, which presented with prolonged impaired awareness seizures for 30-60 s and secondary bilateral tonic seizures. At 9 years of age, brain MRI revealed a left temporal anteroinferior ME with a congenital bone defect in the left middle cranial fossa. She was referred for presurgical epilepsy evaluation. Long-term video electroencephalography (EEG) failed to reveal regional abnormality in the left temporal lobe; invasive evaluation using stereoelectroencephalography (SEEG) was thus indicated. Ictal onset SEEG was identified in the temporal pole near the ME which was rapidly propagated to the mesial temporal structures and other cortical regions. The left temporal pole including the ME was micro-surgically disconnected while preserving the hippocampus and amygdala. The patient's seizures have been completely controlled for 1 year and 6 months post-operatively.

CONCLUSION

SEEG revealed rapid propagation of ictal activity in this patient's case, confirming that the ME was epileptogenic. Since the majority of patients with refractory epilepsy caused by ME have favorable postoperative seizure outcomes, it is important to carefully check for ME in drug-resistant TLE patients with apparently normal MRI.

Virtual reality-based 3-dimensional localization of stereotactic EEG (SEEG) depth electrodes and related brain anatomy in pediatric epilepsy surgery

INTRODUCTION

The increasing use of stereoelectroencephalography (SEEG) in the USA and the need for three-dimensional (3D) appreciation of complex spatial relationships between implanted stereotactic EEG depth electrodes and surrounding brain and cerebral vasculature are a challenge to clinicians who are used to two-dimensional (2D) appreciation of cortical anatomy having been traditionally trained on 2D radiologic imaging. Virtual reality and its 3D renderings have grown increasingly common in the multifaceted practice of neurosurgery. However, there exists a paucity in the literature regarding this emerging technology in its utilization of epilepsy surgery.

METHODS

An IRB-approved, single-center retrospective study identifying all SEEG pediatric patients in which virtual reality was applied was observed.

RESULTS

Of the 46 patients identified who underwent an SEEG procedure, 43.5% (20/46) had a 3D rendering (3DR) of their SEEG depth electrodes. All 3DRs were used during patient-family education and discussion among the Epilepsy multidisciplinary team meetings, while 35% (7/20) were used during neuronavigation in surgery. Three successful representative cases of its application were presented.

DISCUSSION

Our institution's experience regarding virtual reality in the 3D representation of SEEG depth electrodes and the application to pre-surgical planning, patient-family education, multidisciplinary communication, and intraoperative neuronavigation demonstrate its applicability in comprehensive epilepsy patient care.

Semiology, EEG, and neuroimaging findings in temporal lobe epilepsies

Temporal lobe epilepsy (TLE) is the most common type of focal epilepsy. First descriptions of TLE date back in time and detailed portraits of epileptic seizures of temporal origin can be found in early medical reports as well as in the works of various artists and dramatists. Depending on the seizure onset zone, several subtypes of TLE have been identified, each one associated with peculiar ictal semiology. TLE can result from multiple etiological causes, ranging from genetic to lesional ones. While the diagnosis of TLE relies on detailed analysis of clinical as well as electroencephalographic (EEG) features, the lesions responsible for seizure generation can be highlighted by multiple brain imaging modalities or, in selected cases, by genetic investigations. TLE is the most common cause of refractory epilepsy and despite the great advances in diagnostic tools, no lesion is found in around one-third of patients. Surgical treatment is a safe and effective option, requiring presurgical investigations to accurately identify the seizure onset zone (SOZ). In selected cases, presurgical investigations need intracerebral investigations (such as stereoelectroencephalography) or dedicated metabolic imaging techniques (interictal PET and ictal SPECT) to correctly identify the brain structures to be removed.

Stereo-electroencephalography (SEEG) in pediatric epilepsy: Utility in children with and without prior epilepsy surgery failure

BACKGROUND

When noninvasive modalities fail to adequately localize the seizure onset zone (SOZ) in children with medically refractory epilepsy, invasive interrogation with stereo-electroencephalography (SEEG) or subdural electrodes may be required. Our center utilizes SEEG for invasive monitoring in a carefully selected population of children, many of whom have seizures despite a prior surgical resection. We describe the cohort of patients who underwent SEEG in the first 5 years of its employment in our institution, almost half of which had a history of a failed epilepsy surgery.

METHODS

We retrospectively reviewed the records of the first 44 consecutive children who underwent SEEG at Nicklaus Children's Hospital (Miami, Florida), a large, level 4 epilepsy referral center. Patient demographic, clinical, radiographic, and electrophysiological information was collected prospectively. Student's t-test was used for sampling of means and analysis of variance (ANOVA) for evaluation of variance beyond 2 means; chi-square test of independence was used to assess the relationship between categorical variables.

RESULTS

There were 44 patients in this cohort, of whom 17 (38.6 %) were male. The mean age of seizure onset was 6.2 years. Twenty-one patients (47.7 %) had previously failed an epilepsy surgery. Patients with a history of prior epilepsy surgery failure were older at SEEG implantation (17.6 vs. 13.7 years; p = 0.043), were more likely to have SEEG for identification of resection margins (9 vs. 4; p = 0.034), and had fewer electrodes placed (5.9 vs. 7.5; p = 0.016). No difference was seen in complication rates between groups with only 3/297 electrodes placed associated with complications, all of which were minor. Post-SEEG, 29 (65.9 %) patients underwent focal resection, 7 patients had VNS insertion, 3 underwent RNS placement, and 5 had no further intervention. The majority of patients that underwent resection in both groups experienced an improvement in seizures (Engel class I-III), reported by 13/15 (86.7 %) in those naive to surgery and 10/14 (71.4 %) in those with prior surgical failure. Seizure-freedom was much lower in those with prior epilepsy surgery, seen in only 4/14 (28.6 %) versus 8/15 (53.3 %).

CONCLUSION

Our data supports current literature on SEEG as a safe and effective method of electrophysiological evaluation in children naive to surgery and adds that it is a safe technique in children with a history of failed epilepsy surgery. There was no difference in complication rates, which were <1 % in both groups. A favorable outcome was seen in the majority of patients in both groups; the seizure freedom rate, however, was much lower in those with prior epilepsy surgery.

Epilepsy Surgery in Children

Epilepsy in children continues to present a major medical and economic burden on society. Left untreated, seizures can present the risk of sudden death and severe cognitive impairment. It is understood that primary care providers having concerns about abnormal movements or behaviors in children will make a prompt referral to a trusted pediatric neurologist. The authors present a brief introduction to seizure types, classification, and management with particular focus on what surgery for epilepsy can offer. Improved seizure control and its attendant improvements in quality of life can be achieved with timely referral and intervention.

How can the accuracy of SEEG be increased?-an analysis of the accuracy of multilobe-spanning SEEG electrodes based on a frameless stereotactic robot-assisted system

BACKGROUND

A frameless stereotactic robot-assisted system allows stereoelectroencephalography (SEEG) electrodes to span multiple lobes. As the angularity and length are increased, maintaining accuracy of the electrodes becomes more challenging. The goal of this study was to analyze the factors that influence the accuracy of multilobe-spanning SEEG electrodes inserted using a frameless stereotactic robot-assisted system.

METHODS

A total of 322 SEEG electrodes were implanted in 39 patients with refractory epilepsy, and sixty-one multilobe-spanning SEEG electrodes were selected to analyze the factors that influenced the accuracy of implantation. The target error, entrance error, depth error, and angular error were calculated by a specialized computer program. Factors including electrode depth, angular deviation, referencing method, head holder choice, and use of a predrill procedure were analyzed to determine their effects on accuracy.

RESULTS

Thirty-nine patients (aged 2-35 years, median: 19 years; 21 females) underwent frameless robot-assisted SEEG electrode implantation. The mean distance between the intended target and actual tip location was 2.57±1.70 mm (range, 0.42-9.02 mm). The mean distance between the intended entrance point and the actual location was 2.2±1.29 mm (range, 0.70-6.13 mm). The mean length of the electrodes was 84.63±7.61 mm (range, 70.60-103.99 mm). The depth error was 1.36±1.22 mm (range, 0.03-6.69 mm), and the angular deviation was 1.64±1.12 degrees (range, 0.15-4.93 degrees). Multifactor regression analysis showed that entrance error, electrode depth, depth error, angular deviation, referencing method, and head holder choice could explain 59.5% of the electrode target error. Angular deviation, choice of registration approach and head holder and the use of a predrill procedure could explain 48.1% of the electrode entrance error. Use of a predrill procedure significantly reduced the electrode angular deviation (P<0.05).

CONCLUSIONS

Head holder choice, use of a predrill procedure and angular deviation are the primary influencing factors of the accuracy of multilobe-spanning SEEG electrode placement. The Leksell frame and a predrill procedure can be used to increase the accuracy of SEEG electrode placement.

Magnetic Resonance Imaging-Guided Laser Interstitial Thermal Therapy for Epilepsy: Systematic Review of Technique, Indications, and Outcomes

BACKGROUND

For patients with focal drug-resistant epilepsy (DRE), surgical resection of the epileptogenic zone (EZ) may offer seizure freedom and benefits for quality of life. Yet, concerns remain regarding invasiveness, morbidity, and neurocognitive side effects. Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) has emerged as a less invasive option for stereotactic ablation rather than resection of the EZ.

OBJECTIVE

To provide an introduction to MRgLITT for epilepsy, including historical development, surgical technique, and role in therapy.

METHODS

The development of MRgLITT is briefly recounted. A systematic review identified reported techniques and indication-specific outcomes of MRgLITT for DRE in human studies regardless of sample size or follow-up duration. Potential advantages and disadvantages compared to available alternatives for each indication are assessed in an unstructured review.

RESULTS

Techniques and outcomes are reported for mesial temporal lobe epilepsy, hypothalamic hamartoma, focal cortical dysplasia, nonlesional epilepsy, tuberous sclerosis, periventricular nodular heterotopia, cerebral cavernous malformations, poststroke epilepsy, temporal encephalocele, and corpus callosotomy.

CONCLUSION

MRgLITT offers access to foci virtually anywhere in the brain with minimal disruption of the overlying cortex and white matter, promising fewer neurological side effects and less surgical morbidity and pain. Compared to other ablative techniques, MRgLITT offers immediate, discrete lesions with real-time monitoring of temperature beyond the fiber tip for damage estimates and off-target injury prevention. Applications of MRgLITT for epilepsy are growing rapidly and, although more evidence of safety and efficacy is needed, there are potential advantages for some patients.

A systematic exploration of parameters affecting evoked intracranial potentials in patients with epilepsy

BACKGROUND

Brain activity is constrained by and evolves over a network of structural and functional connections. Corticocortical evoked potentials (CCEPs) have been used to measure this connectivity and to discern brain areas involved in both brain function and disease. However, how varying stimulation parameters influences the measured CCEP across brain areas has not been well characterized.

OBJECTIVE

To better understand the factors that influence the amplitude of the CCEPs as well as evoked gamma-band power (70-150 Hz) resulting from single-pulse stimulation via cortical surface and depth electrodes.

METHODS

CCEPs from 4370 stimulation-response channel pairs were recorded across a range of stimulation parameters and brain regions in 11 patients undergoing long-term monitoring for epilepsy. A generalized mixed-effects model was used to model cortical response amplitudes from 5 to 100 ms post-stimulation.

RESULTS

Stimulation levels <5.5 mA generated variable CCEPs with low amplitude and reduced spatial spread. Stimulation at ≥5.5 mA yielded a reliable and maximal CCEP across stimulation-response pairs over all regions. These findings were similar when examining the evoked gamma-band power. The amplitude of both measures was inversely correlated with distance. CCEPs and evoked gamma power were largest when measured in the hippocampus compared with other areas. Larger CCEP size and evoked gamma power were measured within the seizure onset zone compared with outside this zone.

CONCLUSION

These results will help guide future stimulation protocols directed at quantifying network connectivity across cognitive and disease states.

Surgical outcomes in patients with epilepsy after viral encephalitis: contribution of SEEG study

Background

Nowadays, few surgery analysis has been reported in cases of epilepsy after viral encephalitis(VE). Herein, this study was to evaluate the efficacy of surgery and capability of stereoelectroencephalography (SEEG) in the definition of the epileptogenic zone (EZ) after VE, and also to explore the relationship between the SEEG features and the surgical outcomes.

Methods

We retrospectively analyzed 10 surgically treated patients that identified to suffer from epilepsy secondary to VE using SEEG, and investigated the SEEG features associated with surgical outcomes in these patients. Besides visual analysis, we used the epileptogenicity index (EI), a semi-quantitative and supplementary tool to evaluate the validity of SEEG in the context of VE.

Results

Among the 10 operated patients, 3 of them became completely seizure-free. The patients who got totally seizure free or significant improvement, the seizure onset was located either in the antero-mesial temporal structures or focal gyrus; patients who got worthwhile improvement or no improvement, the seizure started from multiple brain lobes. The number of electrodes classified as epileptogenic visually involved were closely correlated with EI positive onses.Anatomic areas defined and shown as EZ on MRI by visual assessment were also defined as epileptogenic by the EI in these cases.

Conclusion

Apart from exploring the surgical outcome related to epilepsy after VE, we also bring insight into the relationship between the SEEG features and surgical outcome with the application of the supplementary methods.

Value of ictal and interictal epileptiform discharges and high frequency oscillations for delineating the epileptogenic zone in patients with focal cortical dysplasia

OBJECTIVES

There are different neurophysiological markers of the Epileptogenic Zone (EZ), but their sensitivity and specificity for the EZ is not known in Focal Cortical Dysplasia (FCD) patients.

METHODS

We studied patients with FCD who underwent stereoelectroencephalography (SEEG) and surgery. We marked in the SEEG: (a) typical and atypical interictal epileptiform patterns, (b) ictal onset patterns, and (c) rates of ripples (80-250 Hz) and fast ripples (FRs) (>250 Hz). High frequency oscillations were marked automatically during one hour of deep sleep. Surgical outcome was defined as good (Engel I) or poor (Engel II-IV). We computed the sensitivity and, as a measure of specificity, the false positive rate to identify the EZ, and compared them across the different neurophysiological markers.

RESULTS

We studied 21 patients, 19 with FCD II. Ictal and typical interictal pattern were the markers with highest sensitivity, while the atypical interictal pattern had the lowest. We found no significant difference in specificity among markers. However, there is a tendency that FRs had the lowest false positive rate.

CONCLUSION

The typical interictal pattern has the highest sensitivity. The clinical use of FRs is limited by their low sensitivity.

SIGNIFICANCE

We suggest to analyze the typical interictal pattern first. FRs should be analyzed in a second step. If, for instance, a focus with FRs and no typical interictal pattern is found, this area could be considered for resection.

Usefulness of StereoEEG-based tailored surgery for medial temporal lobe epilepsy. Preliminary results in 11 patients

OBJECTIVE

Surgical options for medial temporal lobe epilepsy (MTLE) include anterior temporal lobectomy (ATL) and selective amygdalohippocampectomy (SAH). Optimal criteria for choosing the appropriate surgical approach remain uncertain. This article reports 11 consecutive cases in which electrophysiological findings of stereoelectroencephalography (SEEG) were used to determine the optimal surgical approach.

PATIENTS AND METHODS

Eleven consecutive patients with MTLE underwent SEEG evaluation and were placed in either the medial or the medial+lateral group based on the findings. Patients in the medial group underwent SAH using the subtemporal approach, and patients in the medial+lateral group underwent SEEG-guided anterior temporal lobectomy. SEEG findings were also compared with other examinations including flumazenil (FMZ)-positron emission tomography (PET), fluorine-18 labeled fluorodeoxyglucose (FDG)-PET, and magnetoencephalography (MEG). Results were evaluated to determine which examinations most consistently identified the epileptogenic zone.

RESULTS

Of the 11 cases, 4 patients were placed in the medial group, and 7 patients in the medial+lateral group. Of patients, 90.9% were classified in class I of the Engel Epilepsy Surgery Outcome Scale, while 72.7% were classified in class I by the International League Against Epilepsy (ILAE) system. Analyzed by group, 100% of the medial group experienced an Engel class I outcome in the medial group, compared to 85.7% in the medial+lateral group. SEEG findings were comparable with FDG-PET results (10 of 11, 91%).

CONCLUSION

Tailored surgery guided by SEEG is an electrophysiologically feasible treatment for MTLE that can result in favorable outcomes. Although seizures are thought to originate in the medial temporal lobe in MTLE, it is important for involvement of the lateral temporal cortex to be also considered in some cases.

Improving recorded volume in mesial temporal lobe by optimizing stereotactic intracranial electrode implantation planning

PURPOSE

Intracranial electrodes are sometimes implanted in patients with refractory epilepsy to identify epileptic foci and propagation. Maximal recording of EEG activity from regions suspected of seizure generation is paramount. However, the location of individual contacts cannot be considered with current manual planning approaches. We propose and validate a procedure for optimizing intracranial electrode implantation planning that maximizes the recording volume, while constraining trajectories to safe paths.

METHODS

Retrospective data from 20 patients with epilepsy that had electrodes implanted in the mesial temporal lobes were studied. Clinical imaging data (CT/A and T1w MRI) were automatically segmented to obtain targets and structures to avoid. These data were used as input to the optimization procedure. Each electrode was modeled to assess risk, while individual contacts were modeled to estimate their recording capability. Ordered lists of trajectories per target were obtained. Global optimization generated the best set of electrodes. The procedure was integrated into a neuronavigation system.

RESULTS

Trajectories planned automatically covered statistically significant larger target volumes than manual plans [Formula: see text]. Median volume coverage was [Formula: see text] for automatic plans versus [Formula: see text] for manual plans. Furthermore, automatic plans remained at statistically significant safer distance to vessels [Formula: see text] and sulci [Formula: see text]. Surgeon's scores of the optimized electrode sets indicated that 95% of the automatic trajectories would be likely considered for use in a clinical setting.

CONCLUSIONS

This study suggests that automatic electrode planning for epilepsy provides safe trajectories and increases the amount of information obtained from the intracranial investigation.