Detection of epileptogenic focal cortical dysplasia by depth, not subdural electrodes

Centers that perform presurgical epilepsy evaluations disagree on whether depth or subdural electrodes represent the optimal technique for invasive recording, especially in seizures originating outside the temporal lobe. A 13-year-old girl with a normal magnetic resonance imaging scan had unlocalized partial onset seizures, despite scalp and subdural grid ictal video/EEG recordings. Repeat video/EEG with depth electrodes showed a discrete site of continuous interictal spiking and seizure onset that was located 2–2.5 cm beneath the surface of the sensory cortex. The resected region showed focal cortical dysplasia and the patient had greater than 95% seizure frequency reduction at 3-year follow-up. We conclude that although subdural electrodes have many advantages when recording seizures outside the temporal lobes, depth electrodes may provide superior recordings when the epileptogenic region is beneath the cortical surface. Received: 2 April 1997 / Accepted: 11 March 1999     

Epileptogenic neocortical networks are revealed by abnormal temporal dynamics in seizure-free subdural EEG

Long-term video electroencephalographic (EEG) recording is currently a routine procedure in the presurgical evaluation of localization-related epilepsies. Cortical epileptogenic zone is usually localized from ictal recordings with intracranial electrodes, causing a significant burden to patients and health care. Growing literature suggests that epileptogenic networks exhibit aberrant dynamics also during seizure-free periods. We examined if neocortical epileptogenic regions can be circumscribed by quantifying local long-range temporal (auto-)correlations (LRTC) with detrended fluctuation analysis of seizure-free ongoing subdural EEG activity in 4 frequency bands in 5 patients. We show here with subdural EEG recordings that the LRTC are abnormally strong near the seizure onset area. This effect was most salient in neocortical oscillations in the beta frequency band (14-30 Hz). Moreover, lorazepam, a widely used antiepileptic drug, exerted contrasting effects on LRTC (n = 2): lorazepam attenuated beta-band LRTC near the epileptic focus, whereas it strengthened LRTC in other cortical areas. Our findings demonstrate that interictal neuronal network activity near the focus of seizure onset has pathologically strong intrinsic temporal correlations. The observed effect by lorazepam on beta-band activity suggests that the antiepileptic mechanism of benzodiazepines may be related to the normalization of LRTC within the epileptic focus. We propose that this method may become a promising candidate for routine invasive and noninvasive presurgical localization of epileptic foci.     

Neurophysiological monitoring for epilepsy surgery: the Talairach SEEG method. StereoElectroEncephaloGraphy. Indications,results, complications and therapeutic applications in a series of 100 consecutive cases

OBJECT OF THE STUDY: In some candidates for epilepsy surgery in whom the decision to operate is difficult to make, invasive presurgical investigations, namely depth electrode recordings, may be needed. The SEEG (StereoElectroEncephaloGraphy) method consists of stereotactic orthogonal implantation of depth electrodes (5 to 15, 11 on average). The object of this study is to clarify the indications for SEEG, to expose its complications, and to display its usefulness in terms of surgical strategy and results. PATIENTS AND METHODS: 100 patients, suffering from drug-resistant epilepsy and selected as candidates for surgical resection, underwent SEEG between 1996 and 2000. A total of 1,118 electrodes were implanted. For each single case, the sites of implantation of the electrodes were chosen in order to determine either the side of the onset of seizures, or the uni- or multilobar feature of them, or a possible operculo-insular propagation from a temporal onset, and also, using direct electrode stimulation, the proximity of speech or motor area. RESULTS: Complications occurred in 5 patients (2 superficial infections, 2 breakages of electrodes, and 1 intracerebral hematoma responsible for death). SEEG was helpful in most (84%) of the 100 patients to confirm or annul surgical indication, and to adjust the extent of the resection. In some cases (14%), SEEG allowed to propose a resection that might have been disputable based solely on noninvasive investigation data. For frontal epilepsy, SEEG was crucial in all cases to delineate the extent of resection. CONCLUSION: SEEG proved to be a relatively safe and a very useful method in 'difficult' candidates for epilepsy surgery. In addition, in some cases the implanted electrodes can be used to perform therapeutic RF thermocoagulation of epileptic foci or networks.     

Multiple SEEG-guided RF-thermolesions of epileptogenic foci

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.     

Electrophysiological investigations in childhood epilepsy surgery

Epilepsy surgery in children is a functional surgery: its goal is to perform the resection of the epileptic brain tissue while sparing the eloquent cortex. Prolonged scalp video-EEGs allow recording of all types of seizures and play a crucial role in localizing the epileptogenic zone. Furthermore, EEG data correlation with clinical and radiological findings provides a guide for the surgical strategy: either resection without further investigations or an invasive recording procedure. In prehemispherotomy evaluation, EEG recordings confirm that limited resections are not indicated and demonstrate that the opposite hemisphere is not involved. If invasive recordings are needed, they consist in foramen ovale electrode insertion, which provides valuable information in mesial temporal lobe epilepsy, stereoelectroencephalography for children older than two years, and subdural grids associated with depth electrodes in infants or when the eloquent areas need to be carefully investigated. Such investigations allow tailoring surgery to each child.     

Nonhabitual seizures in patients with implanted subdural electrodes

The implantation of subdural electrodes has been widely employed in the invasive monitoring of patients with medically refractory epilepsy. The use of subdural electrodes, though, has been associated with rare but occasionally troublesome complications. We report the occurrence of nonhabitual seizures after implanting subdural grid electrodes. Among 57 patients diagnosed with medically refractory epilepsy who were evaluated in our department over a 12-month period, 21 patients underwent craniotomy for subdural grid/strip electrode implantation. Subdural grids and strips (AdTech, Racine, Wisc., USA) were used for continuous video EEG monitoring. In 3 patients, during subdural monitoring, consistent nonhabitual seizure activity was recorded. This was both clinically and electrographically different than the patients' habitual seizures. The patients' nonhabitual seizures disappeared postoperatively after removing the implanted electrodes. The occurrence of nonhabitual seizures, though quite rare, could lead to mislocalization of an epileptogenic focus. This complication might be the result of direct mechanical cortical irritation or chemical irritation caused by blood breakdown products. The occurrence of nonhabitual seizures comes to add itself to the existing list of complications associated with employment of subdural electrodes for invasive monitoring.     

Display of the epileptogenic zone on the frontal cortical surface using dynamic voltage topography of ictal electrocorticographic discharges.

To evaluate the usefulness of computerized brain-surface dynamic voltage topography (DVT) of ictal electrocorticographic (ECoG) discharges to localize and identify epileptogenic areas, 3 patients with intractable frontal lobe epilepsy who underwent epilepsy surgery after chronic subdural electrode recording were assessed. Cortical surfaces and subdural electrodes were photographed during initial surgery to create an electrode map that could be superimposed onto a picture of the brain surface. DVT was performed by calculating sequential amplitudes of ictal ECoG discharges, which were then superimposed onto the cortical and electrode maps. In all cases, DVT clearly identified the ictal onset zone and the early propagation area on the operative field. DVT allowed recognition of spatial relationships between the epileptogenic area and structural abnormalities, functional cortex, and cortical veins; and was useful to decide on the resection area.     

Surgery after intracranial investigation with subdural electrodes in patients with drug-resistant focal epilepsy: outcome and complications

Video-EEG monitoring with intracranial subdural electrodes is a useful assessment tool for the localization of the epileptogenic zone in patients with drug-resistant focal epilepsy. We aimed at assessing the morbidity related to electrode implantation and the surgical outcome in patients who underwent epilepsy surgery after intracranial EEG monitoring. All patients (N?=?58) admitted to our Epilepsy Surgery Centre for drug-resistant focal epilepsy who underwent resective surgery after intracranial monitoring with subdural electrodes and were followed up for at least 2?years were included in the study. Their mean age was 30.4?years (range 8-60?years), 25 (43?%) were female, and 44 (76?%) had a preoperatively detected structural lesion. The mean duration of invasive recording was 2.3?days (range 1-14?days). Extraoperative ECoG allowed the identification of the epileptogenic focus in all cases. The temporal lobe was involved in 21 (36?%) patients, whereas extratemporal foci were identified in 24 (41?%) patients. Thirteen patients (23?%) had multilobar involvement. Functional brain mapping was performed in 15 (26?%) patients. Transient complications related to electrode implantation occurred in three patients. Among patients with evidence of lesion on preoperative MRI, lesionectomy alone was performed in 12 cases (27?%), while it was combined with tailored cortical resection in the remaining cases. Tailored cortical resection was also performed in patients without evidence of lesion on MRI. After resective surgery, transient neurological deficits occurred in five cases, while another patient experienced permanent lateral homonymous hemianopia. At the last follow-up observation, 34 (57?%) patients were seizure-free (Engel class I). This study suggests that invasive EEG recording with subdural electrodes may be useful and fairly safe for many candidates for epilepsy surgery.     

History of epilepsy surgery at The Hospital for Sick Children in Toronto, Canada

OBJECTIVE: To review the development of epilepsy surgery for pediatric patients with intractable epilepsy at The Hospital for Sick Children in Toronto, Canada. METHODS: We retrospectively collected and reviewed published papers regarding pediatric epilepsy surgery since 1930's. RESULTS: First, McKenzie started a hemispherectomy for children. Hendrick established anatomical hemispherectomy for pediatric patients with hemiparesis and intractable seizures since 1964. Hoffman performed anterior temporal lobectomy and neocortical temporal resection for lesional tempolal lobe epilepsy with or without mesial temporal sclerosis since 1974. Thereafter, multimodal neuroimaging studies of CT scan, MRI, and XenonCT, SPECT and PET have been used to identify and remove the epileptogenic lesion and zone. In 1996, magnetoencephalography (MEG) was introduced to localize interictal spike sources and somatosensory evoked fields for children with intractable seizures. Snead and Rutka started subdural grid electrodes that were constructed by scalp video EEG, MRI and MEG findings.The clustered MEG spike source coregistered with the intraoperative neuronavigation system delineated the epileptogenic zone requiring completely excision for neocortical lesional epilepsy from 2000. CONCLUSION: The pediatric epilepsy surgery at the Hospital for Sick Children has been progressing from anatomical hemispherectomy to complete clusterectomy of MEG spikes sources that localized the epileptogenic zone. Cortical excision, lobectomy, hemisphelotomy, corpus callosotomy and vagal nerve stimulation have been applied to appropriate seizure types identified by advanced neurodiagnostic modalities. We furthermore develop non-invasive methods for localizing and understanding the epileptic network in pediatric epilepsy patients with developing brain.     

Complications of invasive subdural grid monitoring in children with epilepsy

OBJECT: This study was performed to evaluate the complications of invasive subdural grid monitoring during epilepsy surgery in children. METHODS: The authors retrospectively reviewed the records of 35 consecutive children with intractable localization-related epilepsy who underwent invasive video electroencephalography (EEG) with subdural grid electrodes at The Hospital for Sick Children between 1996 and 2001. After subdural grid monitoring and identification of the epileptic regions, cortical excisions and/or multiple subpial transections (MSTs) were performed. Complications after these procedures were then categorized as either surgical or neurological. There were 17 male and 18 female patients whose mean age was 11.7 years. The duration of epilepsy before surgery ranged from 2 to 17 years (mean 8.3 years). Fifteen children (43%) had previously undergone surgical procedures for epilepsy. The number of electrodes on the grids ranged from 40 to 117 (mean 95). During invasive video EEG, cerebrospinal fluid leaks occurred in seven patients. Also, cerebral edema (five patients), subdural hematoma (five patients), and intracerebral hematoma (three patients) were observed on postprocedural imaging studies but did not require surgical intervention. Hypertrophic scars on the scalp were observed in nine patients. There were three infections, including one case of osteomyelitis and two superficial wound infections. Blood loss and the amounts of subsequent transfusions correlated directly with the size and number of electrodes on the grids (p < 0.001). Twenty-eight children derived significant benefit from cortical resections and MSTs, with a more than 50% reduction of seizures and a mean follow-up period of 30 months. CONCLUSIONS: The results of this study indicate that carefully selected pediatric patients with intractable epilepsy can benefit from subdural invasive monitoring procedures that entail definite but acceptable risks.     

Subdural and depth electrodes in the presurgical evaluation of epilepsy

Summary From 1987 to 1992, invasive EEG studies using subdural strips, grids or depth electrodes were performed in a total of 160 patients with medically intractable epilepsy, in whom scalp EEG was insufficient to localize the epileptogenic focus. Dependent on the individual requirements, these different electrode types were used alone or in combination. Multiple strip electrodes with 4 to 16 contacts were implanted in 157 cases through burrholes, grids with up to 64 contacts in 15 cases via boneflaps, and intrahippocampal depth electrodes in 36 cases using stereotactic procedures. In every case, localization of the electrodes with respect to brain structures was controlled by CT scan and MRI.Visual and computerized analysis of extra-operative recordings allowed the localization of a resectable epileptogenic focus in 143 patients (89%), who subsequently were referred for surgery, whereas surgery had to be denied to 17 patients (11%). We did not encounter any permanent morbidity or mortality in our series.In our experience, EEG-monitoring with chronically implanted electrodes is a feasible technique which contributes essentially to the exact localization of the epileptogenic focus, since it allows nearly artefact-free recording of the ictal and interictal activity. Moreover, grid electrodes can be used for extra-operative functional topographic mapping of eloquent brain areas.     

Pure lesionectomy versus tailored epilepsy surgery in treatment of cavernous malformations presenting with epilepsy

Cerebral cavernous malformations (CM) are well-circumscribed vascular malformations that often present with epileptic seizures. Although patients may initially benefit from antiepileptic drugs, surgical treatment may become necessary due to medically intractable seizures. However, it is unclear whether lesionectomy alone or tailored epilepsy surgery with previous invasive monitoring is the optimal strategy in such cases. We report two patients with epileptic seizures due to CM. One patient with few seizures prior to surgery became seizure-free following resection of the CM and the surrounding tissue. In the second patient with long-lasting epilepsy, lesionectomy was performed because of the proximity to a functioning left hippocampus. This limited resection failed and the patient still had seizures. Subsequently, invasive monitoring with intracranial depth and strip electrodes was performed in order to localize the epileptogenic area and determine whether the left hippocampus could be spared. The invasive study showed the seizure origin in the tissue around the former CM but no epileptic discharges in the hippocampus. In a second operation, an anterior temporal resection was performed with removal of the epileptogenic surrounding tissue and the patient became seizure-free without cognitive deficits. The optimal surgical strategy for CM presenting with epileptic seizures must take into account various factors such as underlying mechanisms and duration of epilepsy, and location of the lesion.     

Abolition of spindle oscillations and 3-Hz absence seizurelike activity in the thalamus by using high-frequency stimulation: potential mechanism of action

OBJECT: The mechanism of action whereby high-frequency stimulation (HFS) in the thalamus ameliorates tremor and epilepsy is unknown. The authors studied the effects of HFS on thalamocortical relay neurons in a ferret in vitro slice preparation to test the hypothesis that HFS abolishes synchronized oscillations by neurotransmitter release. METHODS: Intracellular and extracellular electrophysiological recordings were made in thalamic slices. The neurons in the thalamic slice spontaneously generated spindle oscillations, and treatment with picrotoxin, a gamma-aminobutyric acid A receptor antagonist, resulted in 3- to 4-Hz absence seizurelike activity. High-frequency stimulation (stimulation parameters: 10-1000-microA amplitude; l00-microsec pulse width; 100-Hz frequency; 1-60 seconds) was applied using a concentric bipolar stimulating electrode placed adjacent to the recording electrodes. High-frequency stimulation within the thalamus generated inhibitory and excitatory postsynaptic potentials, membrane depolarization, an increase in action potential firing during the stimulation period, and abolished the spindle oscillations in the thalamocortical relay neurons. High-frequency stimulation applied to 20-microM picrotoxin-treated slices eliminated the 3- to 4-Hz absence seizurelike activity. CONCLUSIONS: High-frequency stimulation eliminates spontaneous spindle oscillations and picrotoxin-induced absence seizurelike activity in thalamic slices by synaptic neurotransmitter release; thus, HFS may abolish synchronous oscillatory activities such as those that generate tremor and seizures. Paradoxically, HFS, which is excitatory, and surgical lesions of the ventrointermedius thalamus, which are presumably inhibitory, both suppress tremors. This paradox is resolved by recognizing that HFS-mediated neurotransmitter release and thalamic surgery both disrupt the circuit generating tremor or seizure, albeit by different mechanisms.     

Magnetoencephalography in presurgical epilepsy evaluation

The introduction of whole-head magnetoencephalography (MEG) systems facilitating simultaneous recording from the entire brain surface has led to a major breakthrough of MEG in presurgical epilepsy evaluation. Localizations of the interictal spike zone with MEG showed excellent agreement with invasive electrical recordings, were useful to clarify the spatial relationship of the irritative spike zone to structural lesions, and could attribute epileptic activity to lobar subcompartments both in temporal lobe and extratemporal epilepsy. MEG was especially useful for the study of patients with nonlesional neocortical epilepsy and of patients with large lesions, where it provided unique information on the epileptogenic zone. It could reliably localize sensorimotor cortex prior to surgical procedures adjacent to central fissure. MEG language mapping yielded concordant results with the Wada test and cortical stimulation studies. MEG localizations of epileptic activity and essential brain regions were successfully integrated into frameless stereotaxy systems providing accurate functional information intraoperatively. Because MEG and EEG yield both complementary and confirmatory information, combined MEG-EEG recordings in conjunction with advanced source modeling techniques will further improve the noninvasive evaluation of epilepsy patients and constantly reduce the need for invasive procedures. Electronic Publication     

Modifications of temporal lobectomy according to the extent of epileptic foci and speech-related areas

The authors applied combined depth and subdural electrodes in patients with intractable complex partial seizures to detect the precise extent of epileptic foci and functionally map speech-related areas. The medial temporal structures were explored with depth electrodes and the lateral temporal cortex with subdural electrodes. On the speech-dominant side, electrical stimulation was given to demarcate the speech-related areas in the lateral temporal cortex. Based on these data, the extent of surgical resections was tailored to include as much of the epileptogenic areas as possible while preserving the functionally essential zones of the lateral cortex. According to the range of resection, three different approaches were employed for en bloc ablation of the lateral cortex and opening of the inferior ventricle. The results thus acquired have been satisfactory in terms of seizure control and the preservation of speech function.     

Angiocentric glioma and surrounding cortical dysplasia manifesting as intractable frontal lobe epilepsy--case report

A 26-year-old man presented with a case of angiocentric glioma manifesting as medically refractory epilepsy. Magnetic resonance imaging revealed a hyperintense lesion in the right superior frontal gyrus on T(2)-weighted imaging, with cortical hyperintense rim on T(1)-weighted images and minimum contrast enhancement. Video-electroencephalography (EEG) monitoring characterized his seizures as originating from the right frontal lobe. Long-term EEG recording from implanted subdural electrodes disclosed epileptic activities extending beyond the margin of the radiological lesion. Extended cortical resection of the superior frontal gyrus including the tumor and the surrounding epileptic cortices was performed. Postoperatively, he became seizure-free with antiepileptic medication during a 12-month follow-up period. Histological examination of the surgical specimen showed the characteristic findings of angiocentric glioma. Associated cortical dyslamination consistent with cortical dysplasia was found in the surrounding cortex. Angiocentric glioma is a slow-growing or stable tumor frequently presenting with intractable epilepsy. Surgical treatment would be aimed primarily at control of epilepsy. Complete lesionectomy usually results in postoperative seizure freedom, but the present case shows evidence for associated cortical dysplasia with this tumor entity. Careful pre-surgical evaluation for epilepsy is necessary to achieve better seizure outcome.     

Nonlesional central lobule seizures: use of awake cortical mapping and subdural grid monitoring for resection of seizure focus

OBJECT: Surgical treatment options for intractable seizures caused by a nonlesional epileptogenic focus located in the central sulcus region are limited. The authors describe an alternative surgical approach for treating medically refractory nonlesional perirolandic epilepsy. METHODS: Five consecutive patients who were treated between 1996 and 2000 for nonlesional partial epilepsy that had originated in the central lobule were studied. The patients' ages ranged from 16 to 56 years (mean 28.6 years; there were four men and one woman). The duration of their epilepsy ranged from 8 to 39 years (mean 20.2 years), with a mean seizure frequency of 19 partial seizures per week. Preoperative assessment included video electroencephalography (EEG) and subtracted ictal-interictal single-photon emission computerized tomography coregistered with magnetic resonance imaging (SISCOM). Patients underwent an awake craniotomy stereotactically guided by the ictal EEG and SISCOM studies. Cortical stimulation was used to identify the sensorimotor cortex and to reproduce the patient's aura. A subdural grid was then implanted based on these results. Subsequent postoperative ictal electrocorticographic recordings and cortical stimulation further delineated the site of seizure onset and functional anatomy. During a second awake craniotomy, a limited resection of the epileptogenic central lobule region was performed while function was continuously monitored intraoperatively. One resection was limited to the precentral gyrus, two to the postcentral gyrus, and in two the excisions involved regions of both the pre- and postcentral gyri. In three patients a hemiparesis occurred postsurgery but later resolved. In the four patients whose resection involved the postcentral gyms, transient cortical sensory loss and apraxia occurred, which completely resolved in three. Two patients are completely seizure free, two have experienced occasional nondisabling seizures, and one patient has benefited from a more than 75% reduction in seizure frequency. The follow-up period ranged from 2 to 5.5 years (mean 3.5 years). CONCLUSIONS: A limited resection of the sensorimotor cortex may be performed with acceptable neurological morbidity in patients with medically refractory perirolandic epilepsy. This procedure is an alternative to multiple subpial transections in the surgical management of intractable nonlesional epilepsy originating from the sensorimotor cortex.     

Effect of fentanyl and naloxone on a thalamic induced painful response in intractable epileptic patients

Acute high-frequency (60/s) high-intensity (2,100-2,300 microA) stimulation of the mesial, caudal and inferior portion of the centromedian thalamic region within or close to the parafascicular nucleus produced a sharp, intense, cramp-like painful response localized to the face and shoulder (medial stimulation) or arm and hand (lateral stimulation) contralateral to the stimulation site in 4 intractable epileptic patients in whom depth electrodes had been implanted as a part of a neuroaugmentive procedure for seizure control. This thalamic induced painful response was always accompanied by objective clinical signs (facial gesticulation and contraction of the corresponding muscles) during thalamic stimulation and significant increments in EEG, EKG and respiratory frequencies and EMG muscular tonus from 10 s before to 10 s after thalamic stimulation. Opioid agonists (fentanyl 5.0 microg/kg) and antagonists (naloxone 3.5 microg/kg) were administered to induce and regulate a state of neuroleptanalgesia used for the subcutaneous internalization of the chronic stimulation systems. Under these conditions, we observed that fentanyl greatly attenuated and naloxone increased the intensity of the painful response, as well as the EEG, somatic and vegetative parameters evaluating such a painful response. Differences were significant when one compares the changes in response to electrical stimulation in EEG, EKG, respiration and EMG after the administration of fentanyl (decrease p = 0.001) and naloxone (increase p = 0.01) compared to those obtained after the administration of saline or no drugs during baseline recordings. These data suggest that this thalamic induced painful response is mediated by inhibition or activation of the morphine receptors of the thalamic cells primarily related to the pain process.     

Recent Advancement of Technologies and the Transition to New Concepts in Epilepsy Surgery

Fruitful progress and change have been accomplished in epilepsy surgery as science and technology advance. Stereotactic electroencephalography (SEEG) was originally developed by Talairach and Bancaud at Hôspital Sainte-Anne in the middle of the 20th century. SEEG has survived, and is now being recognized once again, especially with the development of neurosurgical robots. Many epilepsy centers have already replaced invasive monitoring with subdural electrodes (SDEs) by SEEG with depth electrodes worldwide. SEEG has advantages in terms of complication rates as shown in the previous reports. However, it would be more indispensable to demonstrate how much SEEG has contributed to improving seizure outcomes in epilepsy surgery. Vagus nerve stimulation (VNS) has been an only implantable device since 1990s, and has obtained the autostimulation mode which responds to ictal tachycardia. In addition to VNS, responsive neurostimulator (RNS) joined in the options of palliative treatment for medically refractory epilepsy. RNS is winning popularity in the United States because the device has abilities of both neurostimulation and recording of ambulatory electrocorticography (ECoG). Deep brain stimulation (DBS) has also attained approval as an adjunctive therapy in Europe and the United States. Ablative procedures such as SEEG-guided radiofrequency thermocoagulation (RF-TC) and laser interstitial thermal therapy (LITT) have been developed as less invasive options in epilepsy surgery. There will be more alternatives and tools in this field than ever before. Consequently, we will need to define benefits, indications, and limitations of these new technologies and concepts while adjusting ourselves to a period of fundamental transition in our foreseeable future.     

Subcortical EEG changes in rhesus monkeys following experimental hyperextension-hyperflexion (whiplash)

A controlled study, involving EEG recordings from the scalp and chronically implanted electrodes in the cortex (ECoG), as well as from selected subcortical nuclei, was undertaken to investigate the neurophysiologic effects on rhesus monkeys following experimental whiplash (hyperextension of the head and neck). Sixteen animals, equally divided into four groups, were studied through the following protocol: (1) two animals within each group were whiplashed and then electrodes were implanted into the brain of one; (2) the second two animals were implanted with deep electrodes and then one was whiplashed. Weekly EEG follow-ups showed hippocampal spiking in three of the four whiplashed and then electrode-implanted animals and in one of implanted and then whiplashed animals 6 to 8 weeks postwhiplash. Several results deserve attention. (1) The "whiplash syndrome" owes part of its symptoms to EEG disturbances in the brain. (2) Prior to the onset of spiking, ie, 6 to 8 weeks postwhiplash, practically all scalp, cortical, and subcortical EEG recordings were normal. (3) When hippocampal EEG spiking did take place, only normal and mildly abnormal changes were seen in either the electrocorticogram (ECoG) or scalp electroencephalogram (EEG). (4) The growth and development of this trauma-induced hippocampal spiking followed the classic sequence for the spread of an epileptogenic focus. (5) This apparent subclinical form of posttraumatic epilepsy may be due to the combined effects of the whiplash plus the subcortical electrode placements further decreasing the already well-known, low-spiking threshold of the hippocampi.