Depth Electrode Recordings Research Articles

Hypothalamic hamartoma causing gelastic seizures treated with stereotactic radiofrequency thermocoagulation

To present a case of small hypothalamic hamartoma (HH) causing gelastic seizures and treated with stereotactic radiofrequency thermocoagulation. A 22-year-old man presented with intractable gelastic seizures and focal seizures refractory to medical treatment. Magnetic resonance imaging showed a 6 mm x 6 mm x 7 mm sessile intraventricular HH. Under local anesthesia, four intra-hamartoma lesions were made via stereotactic radiofrequency thermocoagulation using a depth electrode for recording and stimulation. Transient central hyperthermia, hypertension, and tachycardia were observed during the coagulation procedure. Intra-hamartoma spikes and slow waves were identified on depth electrode recordings. No gelastic seizure was induced by deep stimulation. The patient was seizure-free during the 12-month follow up and no permanent surgical complications occurred. Stereotactic radiofrequency thermocoagulation may be an effective and safe treatment option in selected cases of hypothalamic hamartoma with gelastic seizures.

Physiology of epilepsia partialis continua and subcortical mechanisms of status epilepticus

Physiology of epilepsia partialis continua and subcortical mechanisms of status epilepticus

The design and hardware implementation of a low-power real-time seizure detection algorithm

Epilepsy affects more than 1% of the world's population. Responsive neurostimulation is emerging as an alternative therapy for the 30% of the epileptic patient population that does not benefit from pharmacological treatment. Efficient seizure detection algorithms will enable closed-loop epilepsy prostheses by stimulating the epileptogenic focus within an early onset window. Critically, this is expected to reduce neuronal desensitization over time and lead to longer-term device efficacy. This work presents a novel event-based seizure detection algorithm along with a low-power digital circuit implementation. Hippocampal depth-electrode recordings from six kainate-treated rats are used to validate the algorithm and hardware performance in this preliminary study. The design process illustrates crucial trade-offs in translating mathematical models into hardware implementations and validates statistical optimizations made with empirical data analyses on results obtained using a real-time functioning hardware prototype. Using quantitatively predicted thresholds from the depth-electrode recordings, the auto-updating algorithm performs with an average sensitivity and selectivity of 95.3 ± 0.02% and 88.9 ± 0.01% (mean ± SEα = 0.05), respectively, on untrained data with a detection delay of 8.5 s [5.97, 11.04] from electrographic onset. The hardware implementation is shown feasible using CMOS circuits consuming under 350 nW of power from a 250 mV supply voltage from simulations on the MIT 180 nm SOI process.

High gamma parietal and prefrontal activity during saccade decision and preparation revealed by depth electrode recordings in humans

High gamma parietal and prefrontal activity during saccade decision and preparation revealed by depth electrode recordings in humans

Introduction Posttraumatic epilepsy: Treatable epileptogenesis

Introduction Posttraumatic epilepsy: Treatable epileptogenesis

Analysis of dynamics and propagation of parietal cingulate seizures with secondary mesial temporal involvement

Cingulate-onset seizures, particularly those originating from parietal cingulate regions, are inadequately described and confounded by patterns of propagation. We analyzed scalp and depth electrode recordings in a patient whose seizures originated from a lesion in the right posterior cingulate region and produced secondary seizure activity in ipsilateral mesial temporal structures. Analyses included the matching pursuit (MP) method of time-frequency decomposition and the Gabor atom density (GAD) measure of signal complexity. Although scalp recordings suggested a right temporal onset, seizures recorded with depth electrodes clearly began in the parietal cingulate region before producing a secondary discharge in ipsilateral mesial structures. GAD revealed a significant increase in complexity during ictal cingulate activity and a consistent pattern of subsequent complexity changes in the hippocampus 30 seconds later. MP and GAD measures were valuable supplements to confirm the stereotyped pattern of both time-frequency changes and complexity. This provides additional evidence for pathways between the parietal cingulate region and mesial temporal structures and raises questions as to whether parietal cingulate seizures can produce clinical symptoms independent of regional or remote propagation.

Investigators' Workshop Sunday Afternoon Session I�2:15 p.m.-3:45 p.m.

Abstract Mary Lou Smith*,† and William D. Gaillard‡*Psychology, University of Toronto, Mississauga, ON, Canada; †Neurology, Hospital for Sick Children, Toronto, ON, Canada and ‡Neurology, Children's National Medical Center, Washington, DC Summary: fMRI has been used successfully in epilepsy patients to map language networks and predict outcome. Only recently has the fMRI of memory begun to elucidate memory networks and inform practice. This IW is designed to provide the current state of fMRI memory investigations and applications in patients with localization related epilepsy. Dr. Mary Pat McAndrews will discuss work on activation in the mesial temporal regions and other components of the autobiographical memory network. She will focus on the relationship of activation strength to pre- and post-operative memory performance as well as electrophysiological data from patients with depth electrode recordings. Dr Silvia Bonelli will present data on material-specific based paradigms targeted to activate mesial temporal regions and their relationship to post operative memory outcomes. This work will also examine the issue of functional capacity vs. functional reserve in relation to hippocampal activation and surgical outcomes. Dr Madison Berl will present investigations on working memory with emphasis on the complicated relationships between working memory and language. The workshop will focus on obstacles to fMRI memory investigations, challenges of paradigm design and execution, and confounding factors of cross domain interference, and outcomes determination.

Explorations préchirurgicales des épilepsies pharmacorésistantes par stéréo-électro-encéphalographie : principes, technique et complications

In the stereo-electro-encephalography (SEEG) methodology developed by Talairach and Bancaud in Sainte-Anne Hospital in Paris, France, the objective of placing depth electrode recordings in presurgical evaluation is to study the spatial and temporal organization of a seizure. This defines for each patient the cortical onset zone, the propagation pattern of the seizure, and the possible involvement of eloquent areas of the cortex. This methodology requires a meticulous stereotactic surgical technique. We report here the SEEG methodology, surgical technique, and morbidity.

La thermocoagulation multiple de foyers épileptogènes guidée par la SEEG (thermo-SEEG)

In many patients with drug-resistant partial epilepsy, depth electrode recordings may be required to delineate the best region for cortical resection. We usually implant depth electrodes according to Talairach's stereoelectroencephalography (SEEG) methodology. Using these chronically-implanted depth electrodes, it is possible to generate radiofrequency (RF) thermolesions of the epileptic foci and networks. The advantages of this type of technique are supported by several lines of evidence, in particular, the high number of implanted electrodes makes it possible to generate several thermolesions, whereas the bleeding risk is null, since no additional electrode trajectory is required.Lesions are generated using 100- to 120-mA bipolar current (50V), applied for 10–40s within the epileptogenic zone, as identified by the SEEG recordings. No general or neurological complication occurred during the procedures.Forty-three patients investigated with video-SEEG recordings for presurgical assessment of drug-resistant partial epilepsy were treated using SEEG-guided RF-thermolesions of the epileptic foci between 2001 and 2006, with a follow-up ranging from 12 to 66 months. Three patients were seizure-free and 52% of the patients had a decrease in their seizure frequency of at least 50%. Of the patients presenting a malformation of cortical development etiology (i.e. dysplasia or heterotopia), 70% were classified as responders (at least a 50% decrease in seizure frequency) (p=0.052), whereas the results were less favorable in patients with a cryptogenic and hippocampal sclerosis etiology. Twenty patients underwent conventional cortectomy in a second step, 18 of whom are in Engel class I. In conclusion, SEEG-guided RF-thermolesions of the epileptic foci and networks proved to be a safe therapeutic procedure capable of providing an immediate benefit in terms of seizure control, especially in patients with epilepsy symptomatic of cortical development malformation. Such thermolesions do not preclude subsequent conventional surgery in case of failure, which can be proposed as an alternative procedure if no resective surgery is possible.

Depth electrode recordings show double dissociation between pitch processing in lateral Heschl’s gyrus and sound onset processing in medial Heschl’s gyrus

Pitch is a fundamental perceptual attribute of sounds. Our ability to discriminate, separate, and identify sounds relies heavily on pitch. Recent neuroimaging studies in humans have provided converging evidence for the existence of a "pitch center"--a region on the superior temporal plane (STP) lateral to Heschl's gyrus specialized in pitch extraction--but a direct confirmation is still missing. Intracerebral recordings in humans are ideally suited for such a confirmation. Here we report results from depth electrode recordings in a patient undergoing investigation for epilepsy. We demonstrate a double dissociation between responses from the medial and lateral STP around Heschl's gyrus to the onset of sound energy and the onset of pitch. Three pieces of evidence support this finding: (1) the response to sounds that do not contain pitch is small in the lateral STP compared to the medial STP; (2) sounds that contain pitch evoke a strong response in the lateral STP; (3) at the transition from noise to a specialised noise-like, but tonal, sound referred to as iterated ripple noise, where the onset of pitch is the sole acoustic event, only the lateral contact showed a response. Our results provide direct evidence for a pitch-specific area on lateral STP with intracranial recordings from the human auditory cortex.

Mapping and assessment of epileptogenic foci using frequency-entropy templates

Much effort has been devoted to developing analysis methods of subdural electroencephalogram and depth electrode recordings of epileptic patients being evaluated for surgical resection. The general approach is to investigate the brain activity at different locations as recorded by the different electrodes in an attempt to localize the epileptogenic focus or foci. Currently, most of the methods are based on the notion that epileptogenic brain activity is associated with changes in synchronization and in complexity. Here we present a method that is based on the temporal dynamics combined with the spectral distribution of energy in terms of frequency-entropy (FE) templates. The FE templates are based upon maximum information partitioning into a set of frequency bands. The FE template is calculated by wavelet packet decomposition followed by an application of the best basis algorithm minimizing the entropy cost function. A comparison between two FE templates is performed by a special quantitative similarity measure according to the overlap in the partitioning into frequency bands and weighted by the bands' entropy. For localization of the epileptogenic foci, the templates of each electrode during the interictal period are compared with a representative template evaluated from the ensemble of all electrodes during the ictal period. We suggest associating the locations that reveal high template similarity to the ictal template with the epileptogenic foci. To test the method and the underlying assumptions, we perform retrospective analysis of the recorded brain activity, from both grid and depth electrodes, from 11 patients suffering from medically intractable epilepsy. Application of the ictal-interictal FE template similarity analysis revealed regions in the epileptic brain in which the interictal characteristics are highly similar to those of the ictal period. To asses the foci we compared the interictal templates of the different electrodes to each other, forming interelectrode similarity matrices. Investigation of these similarity matrices revealed the existence of a single distinct subcluster of electrodes with high interelectrode similarity in the brain activity of seven patients (type-I activity), and the existence of multiple high interelectrode similarity subclusters in the activity of four patients (type-II activity). Comparisons of the analysis results to the medical presurgical evaluations and the outcomes of the surgical resections suggest that the method may be helpful in the chronic evaluation of the epileptogenic zone before operation, and in some cases (type-I activity) without the need to wait for seizures to occur.

Autonomic consequences: Why the most severe seizures are not always the most disturbing

In the literature, tachycardia and hypertension are impressively common in all types of seizures. With implanted depth electrode recording, a predominant laterality of seizures causing tachycardia has not been consistently found. Rather, spread of seizures seems to be necessary to produce tachycardia, and changes in heart rate are likely correlated with the extent of cortex involved. Studies of ictal bradycardia in the setting of focal seizures indicate a modest but clear left-sided predominance for the epileptogenic site, particularly for seizures originating in medial temporal or frontal areas.

Historical evolution of stereotactic amygdalotomy for the management of severe aggression

Friedrich Goltz first reported in the 1890s that temporal lobe removal had a taming effect in animals. The results of studies by Klüver and Bucy, and later Terzian and Ore, demonstrated that an amygdalectomy combined with a temporal lobectomy had a significant taming effect in both animals and humans. Based on these observations, Narabayashi and colleagues reported the first clinical series of patients with temporal lobe epilepsy and/or severe behavioral disturbances in which stereotactic amygdalotomy was performed to address aggressive disorders, using a frame-based stereotactic device designed by Narabayashi. Use of pneumoencephalography, combined with physiological localization by means of olfactory stimulation and field potential recordings, enabled these investigators to define the lateral part of the amygdala, while simultaneously using wax injections to create lesions. Chitanondh used a similar localization technique to produce medial amygdala lesions by injecting a mixture of olive oil, wax, and iodized oil. In 1966, Heimburger and coworkers reported results from a series of 25 patients with epilepsy and aggressive behavior who underwent stereotactic amygdalotomy. Their technique was slightly different and their target localization was solely anatomical, based on pneumoencephalography or contrast ventriculography, and they utilized a cryoprobe to make lesions. In 1970, Balasubramaniam and Ramamurthi reported the largest clinical series to date on this technique; pneumoencephalography or contrast ventriculography was used for anatomical localization, and depth electrode recordings were used to obtain physiological confirmation of their targets, whereas either diathermy or a Bertrand loop was used for making lesions. The development of magnetic resonance imaging technology in late 1980 allowed for a more accurate anatomical localization of the amygdala, and the improvement of radiofrequency generators also made lesioning more precise. Despite these and subsequent technological advances, the number of amygdalotomies performed has geometrically decreased during the last 20 years.

Definition of the epileptogenic zone in a patient with non‐lesional temporal lobe epilepsy arising from the dominant hemisphere

ABSTRACT Pharmacoresistant epilepsy arising from the dominant temporal region in patients with intact memory and normal anatomical imaging, presents major challenges in the preoperative definition of the epileptogenic zone, and the planning of the extent of the surgical resection. We report on the case of a 42‐year‐old, right‐handed male who presented with recurrent daily seizures that were resistant to antiepileptic drugs. Multiple, non‐invasive (scalp) video‐EEG evaluations revealed focal epilepsy arising from the left fronto‐temporal region. Multiple high resolution MRIs that were performed at multiple Epilepsy Centers failed to show any abnormality. Fluoro‐deoxyglucose PET scan showed extensive, left antero‐mesial temporal hypometabolism, and ictal SPECT showed increased perfusion in the left insula in addition to the left mesial and anterior temporal pole. Neuropsychological testing and intracarotid methohexital testing revealed excellent memory to the left, dominant side. A two‐stage invasive evaluation with subdural grid electrodes followed by depth electrode recordings allowed the localization of the epileptogenic region to the temporal pole. A selective resection of the left temporal pole (that spared the hippocampal formation) resulted in a seizure‐free outcome (one year follow‐up) with no significant consequences on memory function. We conclude that targeted, invasive recording techniques should be used for the accurate localization and delineation of the extent of the epileptogenic zone in cases of suspected, non‐lesional, dominant hemisphere, temporal lobe epilepsy with preserved memory function. The use of the staged invasive approach may increase the chances for memory (function) sparing through tailored, temporal resection.

Clinical Neurophysiology: EEG–Video Monitoring

Clinical Neurophysiology: EEG–Video Monitoring

1H-MRS imaging in intractable frontal lobe epilepsies characterized by depth electrode recording

Presurgical evaluation of frontal lobe epilepsy (FLE) remains a challenging issue and frequently requires invasive depth electrode recording. In this study, we aimed at evaluating the potential usefulness of a non-invasive technique such as proton magnetic resonance spectroscopic imaging ( 1H-MRSI) in the presurgical evaluation of FLE and at investigating the potential electrophysiological correlates of the metabolic disturbances as defined by 1H-MRSI. We compared the distribution of 1H-MRSI abnormalities with the electrophysiological abnormalities defined by stereo-electroencephalography (SEEG) recording in 12 patients presenting with several subtypes of FLE. We also used 12 control subjects in order to obtain normative 1H-MRSI data. We used a multilevel 1H-MRSI protocol to better sample the principal regions of the frontal lobe. We also applied a metabolic mapping technique allowing a visual display of metabolic data. A significant decrease of both N-acetyl-aspartate/phosphocreatine-creatine and N-acetyl-aspartate/(choline-compounds + phosphocreatine-creatine) ratios was observed in regions involved in the epileptogenic zone (EZ) and/or the irritative zone (IZ) compared to regions without electrical abnormalities in the same patients ( P = 0.044 and P = 0.018, respectively), and also compared to controls ( P = 0.004 and P = 0.0001, respectively). No significant differences in metabolic ratios were observed between those regions involved in the EZ and those involved in the IZ only. Our results suggest a link between the relative decrease of N-acetyl-aspartate and the EZ as well as the IZ in FLE. Thus, multilevel 1H-MRSI protocol may add pertinent information during the non-invasive presurgical evaluation of FLE.

Progression from frontal-parietal to mesial-temporal epilepsy after fluid percussion injury in the rat.

We recently described an in vivo model of post-traumatic epilepsy (PTE) in the rat where chronic spontaneous recurrent seizures appear following a single episode of fluid percussion injury (FPI). PTE, studied during the first 2 months post-injury, was focal and seizures originated predominantly from the frontal-parietal neocortex at or around the injury site. However, rarer bilateral seizures originating from a different and undefined focus were also observed. To shed light on the Posttraumatic Epileptogenic mechanisms and on the generation of bilateral seizures, we studied rats up to 7 months post-injury. In vivo paired epidural and depth-electrode recordings indicated that the anterior hippocampus evolves into an epileptic focus which initiates bilateral seizures. The rate of frontal-parietal seizures remained constant over time after 2 weeks post-injury, while the rate of hippocampal seizures greatly increased over time, suggesting that different mechanisms mediate neocortical and hippocampal post-traumatic epileptogenesis. Because of different temporal evolution of these foci, the epileptic syndrome was characterized by predominant frontal-parietal seizures early after injury, but by predominant mesio-temporal seizures at later time points. Pathological analysis demonstrated progressive hippocampal and temporal cortex pathology that paralleled the increase in frequency and duration of bilateral seizures. These results demonstrate that FPI-induced frontal-parietal epilepsy (FPE) progresses to mesial-temporal lobe epilepsy (MTLE) with dual pathology. These observations establish numerous similarities between FPI-induced and human PTE and further validate it as a clinically relevant model of PTE.

Place de la chirurgie dans le traitement de l’épilepsie temporale chez l’adulte

Surgery for temporal lobe epilepsy has made significant progress during the past twenty years: in addition to traditional factors (frequency of partial seizures and relative resistance to medical treatment), the possibilities offered by MRI in a large number of cases to detect the responsible lesion (hippocampal sclerosis in the majority of cases) has led to an increase in the use of surgical methods. Furthermore, other examinations (EEG-video, SPECT Depth-electrode recording) now permit precise localization of the epileptic focus. Surgical techniques have likewise been considerably modified: in parallel to classical temporal lobectomy, new surgical methods offer more restricted resection of the lateral cortex. The results are, on the whole, quite satisfactory, as three-quarters of patients can be considered cured or greatly improved. The length of post-operative follow-up does not seem to influence the quality of the results, as observed by the end of the second year.

Intracranial EEG in temporal lobe epilepsy: location of seizure onset relates to degree of hippocampal pathology.

To determine whether the specific location of electrographic seizure onset in the temporal lobe is related to hippocampal pathology in temporal lobe epilepsy (TLE). Consecutive presurgical patients with scalp EEG-video evidence of TLE and no or mild hippocampal atrophy (HA) on magnetic resonance imaging (MRI) were prospectively studied by using depth and subdural strip electrode recordings to identify the site of the initial ictal discharge (IID). Thirty-four patients had either no or mild HA (HA- group). Four additional patients with moderate or marked HA (HA+ group) who required depth and strip electrodes served as a comparison group. Hippocampal pathology was assessed by MRI volumetrics and histopathologic grade of sclerosis (HS). Thirty-eight patients were investigated. In the HA- group, 10 patients had lobar ictal EEG onsets in the hippocampus (HF), medial paleocortex (MPC), and lateral neocortex (LNC); eight cases had regional IIDs in both HF and MPC; 12 persons had IIDs completely outside the HF; three cases lacked depth electrodes, and only one case (3%) had an IID confined to the HF. By contrast, three (75%) of four HA+ cases had IIDs confined to the HF (p = 0.002). Similarly, in 12 patients with low-grade HS, IIDs confined to the HF area were seen significantly less often than in six cases with high-grade HS (p = 0.025). In this study of a large number of patients with no to mild and a smaller group with moderate to marked HA and HS, the location of seizure onset in the temporal lobe was related to the degree of hippocampal pathology. Absence of HA and low-grade HS was each associated with IIDs in both the hippocampus and medial (with or without lateral) temporal cortex, or only the MPC or LNC. Marked HA and high-grade HS both were associated with IIDs restricted to the HF.

Single-neuron activity in the human supplementary motor area underlying preparation for action.

The supplementary motor area (SMA) is considered critical in the planning, initiation, and execution of motor acts. Despite decades of research, including electrical stimulation mapping in patients undergoing neurosurgery, the contribution of this region to the generation of motor behavior has remained enigmatic. This is a study of single-neuron responses at various stages of a motor task during depth electrode recording in the SMA, pre-SMA, and medial temporal lobe of humans, with the goal of elucidating the disparate roles of neurons in these regions during movements. The patients were undergoing evaluation for epilepsy surgery requiring implantation of intracranial depth electrodes. Single-unit recordings were made during both the execution and mental imagery of finger apposition sequences. Only medial frontal neurons responded selectively to specific features of the motor plan, such as which hand performed the motor activity or the complexity of the sequence. Neuron activity progressively increased before the patient was given a "go" cue for the execution of movements; this activity peaked earlier in the pre-SMA than in the SMA proper. We observed similar patterns of activation during motor imagery and actual movement, but only neurons in the SMA differentiated between imagined and real movements. These results provide support at the single-neuron level for the role of the medial frontal cortex in the temporal organization and planning of movements in humans.