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Neuronal generators of visual evoked potentials in humans: visual processing in the human cortex.

PURPOSE: We wished to define the localization of cortical generators of visual (pattern) evoked potentials (VEP) and the temporal sequence of activation in the occipital region. METHODS: In 4 candidates for epilepsy surgery, a large array of subdural electrodes was placed over occipital areas. Checkerboard pattern reversal stimuli were generated and the epileptogenic focus was localized and functionally mapped. Magnetic resonance imaging did not show any occipital lesions in any of the 4 patients. RESULTS: The area first activated was the lingual gyrus in the mesial occipital lobe (negative potential peaks at approximately 70 ms), followed by an area superior to the calcarine fissure (negative peaks at approximately 80 ms). Later (starting at approximately 90 ms), there were positive potentials over the occipital pole and lingual gyrus, followed by potentials at the lateral occipital lobe. CONCLUSIONS: These data support the idea that VEP are generated in the mesial and lateral occipital cortex by different circumscribed neuronal generators with different latencies of activation. The scalp-recorded N1 and P1 potential peaks most likely derive from the progressive activation of neuronal masses in different regions of the occipital lobe.

Brain Mapping↗

Factors associated with work outcome after anterior temporal lobectomy for intractable epilepsy.

PURPOSE: Whereas the effect of anterior temporal lobectomy on seizure frequency is well recognized, less is known about its impact on work status. METHODS: One hundred thirty-four of 190 consecutive patients with temporal lobectomy participated in this study. Eligibility criteria were developed to ensure that only patients with the potential of achieving specific outcomes were included in the corresponding analyses. RESULTS: After surgery, significantly more patients were independent in activities of daily living (p < 0.001) or able to drive (p < 0.001). Income from work also increased (p < 0.01). Nearly one fifth of the patients who were eligible for analysis had either a gain (8%) or a loss (11%) of full- or of part-time work. Univariate analyses revealed the following factors to be associated with full-time work after surgery: student or full-time work within a year before surgery, full-time work experience before surgery, full- or part-time employment experience before surgery, no disability benefits before surgery, low postsurgical seizure frequency, improved postsurgical seizure control, excellent postsurgical seizure control, driving after surgery, and further education after surgery (p < 0.05). Significant factors on multivariate analysis were being a student or having full-time work within a year before surgery [odds ratio, 16.2 (95% CI, 4.3-60.5)], driving after surgery [15.2 (3.2-72.0)], and obtaining further education after surgery [9.2 (2.2-53.0)]. CONCLUSIONS: Anterior temporal lobectomy for intractable epilepsy improves activities of daily living and the ability to drive. Work outcome of this surgery is influenced by presurgical work experience, successful postsurgical seizure control especially to allow driving, and obtaining further education after surgery.

Activities of Daily Living↗

Seizure lateralization during EEG monitoring in patients with bilateral foci: the cluster effect.

PURPOSE: To determine whether seizures that occur in clusters are more likely to reflect activity of the same focus than are seizures that are widely separated in time. METHODS: EEG monitoring data from 14 patients with bilateral independent seizure onsets were analyzed. Twelve of the 14 patients had surface recordings only, and two had implanted electrodes. Interseizure intervals (ISIs) for 151 seizure pairs were measured. Seizure onsets were classified as right hemispheric, left hemispheric, or indeterminate. Seizure pairs were classified as concordant for hemisphere of onset, discordant, or indeterminate. The relation between seizure-pair concordance and ISI was examined by using univariate analysis and analysis of variance (ANOVA). RESULTS: Both seizures originated from the same hemisphere in 61 (75%) of 81 seizure pairs with ISIs <8 h, compared with 28 (55%) of 51 seizure pairs with ISIs >8 h (p < 0.015). The cluster effect was not more pronounced for ISIs <2 h. ANOVA demonstrated that the relation between ISI and seizure concordance was not a result of the variability in seizure rates among patients. In three patients, the presence of bilateral foci was not demonstrated until more than five seizures were recorded. CONCLUSIONS: Seizures that occur after an ISI of <8 h are more likely to come from the same side as the previous seizure than are those with longer ISIs. Thus clustered seizures should not be given the same weight as seizures widely separated in time. In addition, more than five seizures may sometimes be needed to adequately assess patients being evaluated for epilepsy surgery.

Analysis of Variance↗

Magnetoencephalography/magnetic source imaging in the assessment of patients with epilepsy.

Magnetoencephalographic (MEG) dipole source localization is a particularly promising new tool for noninvasive presurgical evaluation of epileptogenic foci. It is potentially more accurate than EEG localization techniques because magnetic fields are not attenuated or distorted by the skull and scalp, which allows cerebral sources to be modeled more simply. MEC spike and seizure sources are routinely co-registered with the patient's brain MRI for clinical interpretation. This has been called magnetic source imaging. Numerous studies have shown that MEG localization of foci agreed with lesion position, depth electrode and ECoG data, PET and MRI findings, and surgical success. The recent development of whole head sensor arrays has greatly enhanced the case with which epileptiform magnetic fields can be recorded and analyzed.

Brain↗

De novo psychogenic nonepileptic seizures after epilepsy surgery.

PURPOSE: The occurrence of de novo nonepileptic seizures (NES) after epilepsy surgery have been reported only twice in the literature (one article and one abstract). METHODS: We report three patients whose de novo NES were documented by video-EEG telemetry after epilepsy surgery. These patients were drawn from a sample of 166 consecutive patients who underwent epilepsy surgery at our center between 1989 and 1996. RESULTS: Two patients became seizure free after surgery, and one had significant improvement of her seizures. The interval between the date of surgery and the development of the symptoms was variable (8, 10, and 47 months, respectively). The clinical phenomena of NES differed from those of the epileptic seizures preceding surgery. Their diagnosis had not been suspected in two patients before the diagnostic video-EEG monitoring study. After the diagnosis of NES, spells stopped in two patients and recurred rarely in one. CONCLUSIONS: We conclude that de novo NES appears to occur rarely after epilepsy surgery. Given that the possibility of NES was suspected in only one patient, its incidence after surgery may be higher than so far reported. Physicians should therefore consider NES in the differential diagnosis of recurrent seizures after a seizure-free period after epilepsy surgery.

Adult↗

Opercular reflex seizures: a case report with stereo-electroencephalographic demonstration.

Reflex epileptic seizures of opercular origin have been described previously based on video-electroencephalographic monitoring, but very few patients have been explored with depth electrodes. We report a woman with late-onset epilepsy who had intractable seizures despite trials of several antiepileptic drugs. At the time of the depth-electrode recordings, seizures were usually continuous and occurred either spontaneously or were induced by movements of the jaw and mouth. The seizures originated in the deep central opercular cortex; localization was confirmed by a good surgical outcome.

Cerebral Cortex↗

Epilepsy, vagal nerve stimulation by the NCP system, all-cause mortality, and sudden, unexpected, unexplained death.

PURPOSE: This report concerns the 2-year extension of the study of mortality and sudden, unexpected, unexplained death in epilepsy (SUDEP) in the cohort of patients receiving vagal nerve stimulation by the NCP System for the treatment of epilepsy. METHODS: A cohort of 1,819 individuals was followed 3,176.3 person-years from implantation. The 25 deaths that occurred during NCP System activation were reviewed for SUDEP by a panel. RESULTS: The mortality rates were lower [standardized mortality ratio (SMR = 3.6)] with the extended follow-up compared to the previous finding (SMR = 5.3). The SUDEP rates (4.1 vs. 4.5 per 1,000 person-years) were similar to those in the previous study of this cohort. When the vagal nerve stimulation experience is stratified by duration of use, the rate of SUDEP was 5.5 per 1,000 over the first 2 years, but only 1.7 per 1,000 thereafter. CONCLUSIONS: The mortality and SUDEP rates are similar to those reported from clinical trials of new drugs and cohorts of severe epilepsy. The lower SUDEP rates after 2 years of follow-up are intriguing, but require further investigation.

Adolescent↗

Effects of Nefiracetam, a novel pyrrolidone-type nootropic agent, on the amygdala-kindled seizures in rats.

PURPOSE: Nefiracetam (NEF) is a novel pyrrolidonetype nootropic agent, and it has been reported to possess various pharmacologic effects as well as cognition-enhancing effects. The present study focused on the effects of NEF in amygdala-kindled seizures and its potential for antiepileptic therapy. METHODS: Effects of NEF on fully amygdala-kindled seizures and development of amygdala-kindled seizures were investigated in rats and compared with those of levetiracetam (LEV), a pyrrolidone-type antiepileptic drug (AED). RESULTS: In fully amygdala-kindled rats, NEF (25, 50, and 100 mg/kg, p.o.) decreased afterdischarge induction, afterdischarge duration, seizure stage, and motor seizure duration in a dose-dependent manner. LEV (25, 50, and 100 mg/kg, p.o.) had no effects on afterdischarge induction and slightly decreased afterdischarge duration, whereas it markedly decreased seizure stage and motor seizure duration. In contrast to the results in fully amygdala-kindled rats, NEF (25 and 50 mg/kg/day, p.o.) had few or no effects on the development of amygdala-kindled seizures. As well as fully amygdala-kindled seizures, LEV (50 mg/kg/day, p.o.) markedly inhibited the development of behavioral seizures without reducing daily afterdischarge duration. CONCLUSIONS: Although NEF possesses potent anticonvulsant effects on fully amygdala-kindled seizures, it has few or no effects on the development of amygdala-kindled seizures. LEV shows marked anticonvulsant effects on both phases of kindling. In fully amygdala-kindled rats, NEF inhibits both electroencephalographic and behavioral seizures, whereas LEV inhibits only behavioral seizures. This double dissociation suggests that NEF has a distinct anticonvulsant spectrum and mechanisms from those of LEV.

Administration, Oral↗

Effects of chronic left vagal stimulation on visceral vagal function in man.

We examined the effects of chronic left vagal electrostimulation on afferent and efferent gastrointestinal vagal function in eight patients. Afferent function was assessed using cortical evoked responses to electrical stimulation of the esophagus and to direct vagal stimulation using the implanted left vagal electrode. Efferent gastrointestinal vagal function was measured by examining the basal, maximal, and sham fed stimulated gastric acid output prior to and with chronic left vagal electrostimulation. Esophageal electrostimulation produced a cortical evoked response consisting of three negative and three positive peaks within 400 msec after stimulation. Prior to vagal electrostimulation the mean conduction velocity of the afferent signal was measured at 8.72 +/- 3.39 m/sec, compatible with A-delta fibers involvement. Basal, maximal, and sham fed acid output were 1.11, 21.87, and 9.37 mmol/hour, respectively. The evoked response to esophageal electrical stimulation was not changed with chronic left vagal electrostimulation. Direct vagal stimulation also produced evoked potentials that were comparable to those obtained with esophageal stimulation. The mean conduction velocity was 6.26 +/- 2.72 m/sec (NS) so that there was no evidence of loss of myelinated fibers with chronic stimulation. No differences were detected in basal (1.29 mmol/h), maximal (21.64 mmol/h), or sham fed stimulated (8.03 mmol/h) acid output, showing that vagal electrostimulation has no effect on either total or vagally mediated acid output, an efferent vagal function. In conclusion, chronic left vagal electrostimulation has no significant adverse effect on gastrointestinal vagal function.

Adult↗

Electrostimulation effects of the vagus nerve on balance in epilepsy.

Preliminary results of selected postural measures in quiet standing indicate that stimulation of the vagus nerve appears not to be producing adverse effects. With this specific sample size, more testing is needed to determine long-term effects and future data analyses will examine correlations between electroencephalogram results, drug levels, and seizure frequency. In the present study three subjects have had old injuries to hips and ankles. Two subjects had normal values for postural control prior to stimulation, while other subjects were severely abnormal. In future, studies should include larger homogeneous sample sizes, as the current subjects show marked variability in age and premorbid health backgrounds. Future work should also control more vigorously for variables such as visual input (i.e., blindfolding subjects instead of simply closing the eyes). Evaluation of postural control mechanisms will be continued to assess stability changes in these patients as seizure frequency continues to subside.

Adult↗

Effect of vagal nerve electrostimulation on the power spectrum of heart rate variability in man.

The power spectrum of heart rate variability contains low frequency (LF = 0.08-0.12 Hz) and high frequency (HF = 0.18-0.30 Hz) components said to represent neurocardiac rhythms. To verify whether such a relationship exists we report a unique study where the heart rate autospectrum was determined in a 28-year-old epileptic male patient with an implanted vagal electrical stimulator. The stimulator was activated at 20 Hz, 300 microseconds pulse, and 1.25 V. Continuous ECG and respiratory waveform records were obtained over 45 minutes every 8 hours (7-8 AM; 3-4 PM; 11-12 PM) with the stimulator ON, then 24 hours OFF and then 24 hours ON again. The overall LF:HF peak ratio increased from 0.64 to 1.99 (P less than 0.001) after the stimulator was turned OFF. There was a dramatic increase in the LF peak power (greater than 60%) and a corresponding decrease in the HF peak power (greater than 65%) when the stimulator was turned OFF. These values were reversed when the stimulator was turned ON again. In the early morning and late evening hours, there was a significant rightward shift in the LF peak power frequency (average 0.057 to 0.075 Hz) whenever the stimulator was ON. Otherwise, there were no significant circadian variations in any of the autospectral components. The results demonstrate an unequivocal relationship between selective vagal nerve electrostimulation and alterations in the heart rate autospectrum.

Adult↗

Reduction of antiepileptic drug dosage for monitoring epileptic seizures.

Eleven epileptic patients, candidates for surgical treatment, were examined in order to localize epileptic foci. The daily doses of antiepileptic drugs (AEDs) were reduced by fifty per cent or less, and the reduced dosages were maintained until a seizure had occurred. The reduction resulted in seizures within five days among all patients, and the number of seizures increased significantly in comparison with the five-day period before AED reduction. The seizures so provoked were typical for each patient, as confirmed by clinical observation and video-EEG telemetry. No status epilepticus or withdrawal psychosis occurred. The AED concentrations at the time of the seizures were generally within the reference values.

Adult↗

Vigabatrin-induced gingival overgrowth.

Vigabatrin is a relatively new medication used in the treatment of epilepsia. The present report concerns the use of vigabatrin by a 19-year-old woman. The patient manifested marked gingival overgrowth compatible clinically and histologically with the overgrowth induced by phenytoin, cyclosporine and calcium channel blockers. This is the 1st report of vigabatrin-induced gingival overgrowth. Clinicians should be aware of similar lesions in patients using new anticonvulsants.

Adult↗

January 1997--7 year old girl with seizures.

A seven year old girl presented with six month history of seizures. An MRI scan showed a cortical lesion in the left temporal lobe which was resected. Neuropathologic examination demonstrated meningioangiomatosis, an unusual hamartomatous condition sometimes associated with neurofibromatosis 2. Approximately 50 cases of meningioangiomatosis have been reported in the literature. These are reviewed and compared to the current case.

Angiomatosis↗