Subdural Electrode Recordings Research Articles

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.

NMDA-receptors 1 and 2A/B coassembly increased in human epileptic focal cortical dysplasia.

This study was designed to quantify the relation between expressions of NMDA receptor (NMDAR) subunits (1 and 2A/B) and the epileptogenicity in human focal cortical dysplasia. Immunoblotting and immunoprecipitation were used to quantify these receptor subunits in tissue resected from EEG-verified epileptic and distal nonepileptic frontal cortical areas in each of three patients as determined by chronic subdural electrode recordings. In each patient, adjacent sections were immunostained to verify that the numbers of dysplastic neurons were greater in epileptic than in nonepileptic cortex. In all patients, NMDAR2A/B expressions and their coassemblies with NMDAR1 were increased in epileptic dysplastic cortex compared with the relatively normal appearing nonepileptic cortex. For all three patients, there were no significant differences in NMDAR1 protein expressions between the two EEG groups. These results suggest that increased NMDAR1-NMDAR2A/B coassembly contributes to hyperexcitability in dysplastic cortical neurons and focal seizure onsets.

Surgical management and seizure outcome in patients with tuberous sclerosis.

The authors report the results obtained in 11 patients with tuberous sclerosis (TS) who underwent cortical resection surgery for medically intractable epilepsy. Patients' ages at time of surgery ranged from 3 to 46 years (mean 19.6 years). Preoperative epileptiform electroencephalographic abnormalities were focal spike wave discharges in six patients (55%), multifocal in four patients (36%), and generalized in one patient (9%). In the multifocal and generalized groups, all patients (45%) were evaluated by means of subdural grid and strip electrode recordings, whereas electrophysiological localization in the remaining patients was derived from ictal and interictal scalp recordings. The seizure foci were found to be extratemporal in six patients (55%) and temporal in five patients (45%). Surgical intervention consisted of craniotomy and seizure foci resection guided by electrocorticographic monitoring and functional mapping in five awake (45%) and six asleep (55%) patients. Neuropathological examination of the resected seizure foci revealed cortical tubers in eight patients and diffuse gliosis in three patients. Follow up ranged from 8 to 127 months (mean 35 months). Six patients (55%) were seizure free, half of whom were not receiving antiepileptic drugs (AEDs); three patients (27%) had a greater than 70% reduction in seizure frequency, although they required AEDs; one patient (9%) had a 50% temporary reduction in seizure frequency during the initial 6-month postoperative period; and one patient (9%) was lost to follow-up study. From this small but adequately followed patient population with TS, the authors conclude that cortical resection of seizure foci tailored to electrocorticographic findings and functional mapping is encouraging for this difficult to manage patient population with medically intractable epilepsy.

Intracerebral depth electrode monitoring in partial epilepsy: the morbidity and efficacy of placement using magnetic resonance image-guided stereotactic surgery.

To determine the indications for, efficacy of, and safety of depth electrode placement using magnetic resonance imaging (MRI)-guided stereotactic surgery in patients with intractable epilepsy. We analyzed retrospectively the results of depth electrode usage in 50 consecutive patients at the University of Michigan Hospitals studied in the years 1991 through 1994, using MRI-guided stereotactic implantation, in conjunction with simultaneous subdural strip electrode recordings. There were no deaths, no infections, and no new neurological deficits. One small subdural hematoma adjacent to a subdural strip electrode was evacuated to prevent interference with ictal recording. Two cylindrical subdural electrodes were found to be intraparenchymal, as revealed by postoperative MRI, and were removed. One patient was unintentionally left alone briefly, and he pulled out the electrodes while confused postictally, requiring a subsequent operation for replacement. Ictal onset zones were successfully localized in 47 patients. We have found intracerebral electrode placement to be as safe as subdural strip electrode placement and have found combined depth and strip electrode monitoring to be highly effective in localizing the onset zones of complex partial seizures. Intracranial monitoring was particularly useful in the detection of a single ictal onset zone in the absence of neuroimaging abnormality and in the definitive diagnosis of bilateral independent ictal onset zones in the temporal lobe epilepsy syndrome. The specific technical aspects of the procedure that contribute to a successful outcome are reviewed. A comparison with earlier reported series suggests that MRI-guided stereotaxy and pial inspection may reduce complications of depth electrode placement.

Predictability of EEG interictal spikes

To determine whether EEG spikes are predictable, time series of EEG spike intervals were generated from subdural and depth electrode recordings from four patients. The intervals between EEG spikes were hand edited to ensure high accuracy and eliminate false positive and negative spikes. Spike rates (per minute) were generated from longer time series, but for these data hand editing was usually not feasible. Linear and nonlinear models were fit to both types of data. One patient had no linear or nonlinear predictability, two had predictability that could be well accounted for with a linear stochastic model, and one had a degree of nonlinear predictability for both interval and rate data that no linear model could adequately account for.

An intra-arterial electrode for intracranial electro-encephalogram recordings.

A new method for intracranial monitoring of brain electrical activity by means of an intra-arterial guide wire as electrode is described. We carried out intracranial electro-encephalography (EEG) using an insulated Seeker Lite-10 guide wire 18 times in 14 patients: ten times in 6 patients with cerebral arteriovenous malformation (AVM) before embolization, and another 8 times in 8 patients with epilepsy. In all cases, a 2-5 times stronger high voltage potential EEG compared with scalp EEG could be recorded. In 3 patients with complex partial epilepsy, intra-arterial (IA) EEG was recorded under subdural strip electrode monitoring, and IAEEG at the sphenoidal portion of the middle cerebral artery was compared with subdural electrode recordings. Frequent interictal spike discharges recorded with subdural electrodes in the lesional medial temporal lobe were simultaneously visible on IAEEG recording. This method is equivalent to that using a semi-invasive electrode, but ECoG recording can be performed at angiography. IAEEG is a method of electrode recording that has the possibility of clinical application.

Contributions of anterior cingulate cortex to behaviour.

Assessments of anterior cingulate cortex in experimental animals and humans have led to unifying theories of its structural organization and contributions to mammalian behaviour. The anterior cingulate cortex forms a large region around the rostrum of the corpus callosum that is termed the anterior executive region. This region has numerous projections into motor systems, however, since these projections originate from different parts of anterior cingulate cortex and because functional studies have shown that it does not have a uniform contribution to brain functions, the anterior executive region is further subdivided into 'affect' and 'cognition' components. The affect division includes areas 25, 33 and rostral area 24, and has extensive connections with the amygdala and periaqueductal grey, and parts of it project to autonomic brainstem motor nuclei. In addition to regulating autonomic and endocrine functions, it is involved in conditioned emotional learning, vocalizations associated with expressing internal states, assessments of motivational content and assigning emotional valence to internal and external stimuli, and maternal-infant interactions. The cognition division includes caudal areas 24' and 32', the cingulate motor areas in the cingulate sulcus and nociceptive cortex. The cingulate motor areas project to the spinal cord and red nucleus and have premotor functions, while the nociceptive area is engaged in both response selection and cognitively demanding information processing. The cingulate epilepsy syndrome provides important support of experimental animal and human functional imaging studies for the role of anterior cingulate cortex in movement, affect and social behaviours. Excessive cingulate activity in cases with seizures confirmed in anterior cingulate cortex with subdural electrode recordings, can impair consciousness, alter affective state and expression, and influence skeletomotor and autonomic activity. Interictally, patients with anterior cingulate cortex epilepsy often display psychopathic or sociopathic behaviours. In other clinical examples of elevated anterior cingulate cortex activity it may contribute to tics, obsessive-compulsive behaviours, and aberrent social behaviour. Conversely, reduced cingulate activity following infarcts or surgery can contribute to behavioural disorders including akinetic mutism, diminished self-awareness and depression, motor neglect and impaired motor initiation, reduced responses to pain, and aberrent social behaviour. The role of anterior cingulate cortex in pain responsiveness is suggested by cingulumotomy results and functional imaging studies during noxious somatic stimulation. The affect division of anterior cingulate cortex modulates autonomic activity and internal emotional responses, while the cognition division is engaged in response selection associated with skeletomotor activity and responses to noxious stimuli. Overall, anterior cingulate cortex appears to play a crucial role in initiation, motivation, and goal-directed behaviours.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of implanted dipoles by magnetoencephalography

We attempted to validate the location of sources predicted by magnetoencephalography (MEG) by studying 19 specially designed dipole electrodes implanted in six patients with intractable partial seizures who were undergoing subdural electrode recording. We used a seven-channel magnetometer to measure the magnetic fields produced by passing through the dipoles a 40-microA, 5-msec square-wave pulse followed 40 msec later by a pulse of opposite polarity; 200 pulses were averaged for each magnetometer position. The actual dipole locations were measured from skull radiographs, and we based MEG localization on a spherical head model with the inclusion of volume currents. MEG estimates of the sources were within several centimeters (mean, 1.69 cm) of the measured locations. We conclude that MEG localization was promising.

Principles of Magnetoencephalography

Magnetoencephalography (MEG) is a new, noninvasive functional test equivalent to EEG. It has been used to localize the sources of evoked responses and interictal and ictal epileptiform discharges and to study patients with psychiatric illnesses, cerebrovascular accidents, and migraine. In epilepsy research, it is hoped that MEG will provide information similar to that yielded by depth or subdural electrode recording, or that the combination of these methods will provide more information than either one alone. The application of MEG appears to be widening, although it is not yet a routine clinical diagnostic tool. The utility of MEG is limited by technological problems, but new and more efficient systems are becoming available. Within several years, advances in the technology and understanding of MEG may modify the course of its application.

Subdural electrode recordings for seizure focus localization

Subdural electrode recordings for seizure focus localization

Comparison of scalp to subdural recordings for localizing epileptogenic foci

We reviewed a group of 124 patients who were seizure-free after epilepsy surgery to determine the relative accuracy for identifying epileptogenic foci with (a) interictal scalp recordings, (b) ictal scalp recordings, and (c) ictal subdural electrode recordings. If considering only patients undergoing temporal lobe surgery, ictal subdural strip recordings were accurate in 100% of cases. Ictal scalp recordings were accurate in 44% of cases, whereas interictal scalp recordings were accurate in only 31% of cases. The data also indicate that noninvasive recordings have a false lateralization or localization error rate of 10% when used for identifying unilateral epileptogenic foci in preparation for epilepsy surgery.

Chronic subdural strip electrode recordings for difficult epileptic problems

We report a prospective series of 100 consecutive patients who underwent recordings with chronic subdural strip electrodes to resolve difficult diagnostic and treatment issues regarding medically refractory epilepsy. All patients had previously undergone chronic EEG/video monitoring with scalp with or without sphenoidal electrodes. After subdural strip electrode recordings 62 patients were found to have unilateral epileptogenic foci amenable to surgical resection. These include two patients previously diagnosed as having pseudoseizures. Forty-five patients underwent focal resection and were followed for at least 6 months; 96% are seizure-free or significantly improved. Of the 38% who did not have a focus diagnosed, 22 were found to be candidates for anterior corpus callosotomy. Four patients had inconclusive monitoring results, and 11 patients were found not to be surgical candidates. There has been no morbidity or mortality in this series of patients. We conclude that subdural strip electrode recording is a relatively safe and effective method for resolving difficult diagnostic issues involving the treatment of medically refractory epilepsy.