Opercular to interhemispheric source distribution of benign rolandic spikes of childhood

Insights into epileptic aphasia: Intracranial recordings in a child with a left insular ganglioglioma

Intracranial EEG was recorded during a dialog-based task in a 16-year-old boy with a left insular ganglioglioma, medically intractable epilepsy, epileptic foci in auditory cortex on the lateral superior temporal gyrus (STG) and language deficiencies. Performance of the task was highly erratic, characterized by rapid cycling between providing correct answers, incorrect answers and failure to respond. There was no relationship between performance and the degree of concurrent epileptic activity in auditory cortex. High gamma activity in core auditory cortex (posterior medial Heschl's gyrus, HGPM) was markedly diminished during listening and, with two exceptions, was less than activity from 17 control subjects. The two exceptions also had seizure onset zones in perisylvian cortex. Responses during listening were of smaller amplitude than those occurring during speaking, a pattern opposite that typically seen in the left HGPM. Within HGPM, lateral STG and pars opercularis of the inferior frontal gyrus, high gamma activity while listening was greatest when questions were correctly answered and least when the subject failed to respond. Alpha activity preceding utterances was lowest in pars opercularis when the subject failed to respond. Comparisons between resting state activity in another cohort of controls and the subject were most disparate in HGPM. Alpha activity during performance of the task was greatest in the mid-anterior cingulate when the subject failed to respond, suggesting dysfunction beyond the speech network and into the salience network. Multiple abnormalities noted in this patient paralleled those seen in epileptic aphasia and Rolandic epilepsy.

Practical Fundamentals of Clinical MEG Interpretation in Epilepsy

Magnetoencephalography (MEG) is a neurophysiologic test that offers a functional localization of epileptic sources in patients considered for epilepsy surgery. The understanding of clinical MEG concepts, and the interpretation of these clinical studies, are very involving processes that demand both clinical and procedural expertise. One of the major obstacles in acquiring necessary proficiency is the scarcity of fundamental clinical literature. To fill this knowledge gap, this review aims to explain the basic practical concepts of clinical MEG relevant to epilepsy with an emphasis on single equivalent dipole (sECD), which is one the most clinically validated and ubiquitously used source localization method, and illustrate and explain the regional topology and source dynamics relevant for clinical interpretation of MEG-EEG.

The 10 Common Evidence-Supported Indications for MEG in Epilepsy Surgery: An Illustrated Compendium

Unfamiliarity with the indications for and benefits of magnetoencephalography (MEG) persists, even in the epilepsy community, and hinders its acceptance to clinical practice, despite the evidence. The wide treatment gap for patients with drug-resistant epilepsy and immense underutilization of epilepsy surgery had similar effects. Thus, educating referring physicians (epileptologists, neurologists, and neurosurgeons) both about the value of epilepsy surgery and about the potential benefits of MEG can achieve synergy and greatly improve the process of selecting surgical candidates. As a practical step toward a comprehensive educational process to benefit potential MEG users, current MEG referrers, and newcomers to MEG, the authors have elected to provide an illustrated guide to 10 everyday situations where MEG can help in the evaluation of people with drug-resistant epilepsy. They are as follows: (1) lacking or imprecise hypothesis regarding a seizure onset; (2) negative MRI with a mesial temporal onset suspected; (3) multiple lesions on MRI; (4) large lesion on MRI; (5) diagnostic or therapeutic reoperation; (6) ambiguous EEG findings suggestive of "bilateral" or "generalized" pattern; (7) intrasylvian onset suspected; (8) interhemispheric onset suspected; (9) insular onset suspected; and (10) negative (i.e., spikeless) EEG. Only their practical implementation and furtherance of personal and collective education will lead to the potentially impactful synergy of the two-MEG and epilepsy surgery. Thus, while fulfilling our mission as physicians, we must not forget that ignoring the wealth of evidence about the vast underutilization of epilepsy surgery - and about the usefulness and value of MEG in selecting surgical candidates - is far from benign neglect.

Functional and Structural Network Disorganizations in Typical Epilepsy With Centro-Temporal Spikes and Impact on Cognitive Neurodevelopment

Epilepsy with Centrotemporal Spikes (ECTS) is the most common form of self-limited focal epilepsy. The pathophysiological mechanisms by which ECTS induces neuropsychological impairment in 15-30% of affected children remain unclear. The objective of this study is to review the current state of knowledge concerning the brain structural and functional changes that may be involved in cognitive dysfunctions in ECTS. Structural brain imaging suggests the presence of subtle neurodevelopmental changes over the epileptogenic zone and over distant regions in ECTS. This structural remodeling likely occurs prior to the diagnosis and evolves over time, especially in patients with cognitive impairment, suggesting that the epileptogenic processes might interfere with the dynamics of the brain development and/or the normal maturation processes. Functional brain imaging demonstrates profound disorganization accentuated by interictal epileptic spikes (IES) in the epileptogenic zone and in remote networks in ECTS. Over the epileptogenic zone, the literature demonstrates changes in term of neuronal activity and synchronization, which are effective several hundred milliseconds before the IES. In the same time window, functional changes are also observed in bilateral distant networks, notably in the frontal and temporal lobes. Effective connectivity demonstrates that the epileptogenic zone constitutes the key area at the origin of IES propagation toward distant cortical regions, including frontal areas. Altogether, structural and functional network disorganizations, in terms of: (i) power spectral values, (ii) functional and effective connectivity, are likely to participate in the cognitive impairment commonly reported in children with ECTS. These results suggest a central and causal role of network disorganizations related to IES in the neuropsychological impairment described in ECTS children.

The association of epileptic focus estimated by magnetoencephalography with cognitive function in non-lesional epilepsy with continuous spikes and waves during slow wave sleep (ECSWS) children

OBJECTIVE

Epilepsy with continuous spikes and waves during slow sleep (ECSWS) is associated with cognitive deficits. The underlying mechanism is thought to relate to disturbance of functions of the foci by the persistent epileptic activity. However, the relationship between epileptic foci and cognitive deficits remains largely unknown, except for in Landau-Kleffner syndrome. The aim of this study was to evaluate the relationship of epileptic foci estimated from magnetoencephalography (MEG) with cognitive functions at the period of diagnosis in non-lesional ECSWS children, excluding those with Landau-Kleffner syndrome.

METHODS

MEG data and the Wechsler intelligence scale for children-III scores at ECSWS diagnosis, and medical records, were reviewed. Multiple regression analysis was performed to examine the relationship of parameters of MEG spike dipole clusters, including anatomical location or laterality, with the Wechsler intelligence scale for children-III scores at ECSWS diagnosis.

RESULTS

Sixteen patients were included, all of whom were right-handed. Epilepsy onset (first unprovoked seizure) ranged from 31 to 110 months (mean, 68.5). The age at ECSWS diagnosis ranged from 72 to 156 months (mean, 108.9). The dipole clusters were estimated on the right Rolandic area (RA) in 4 patients (25%), right supramarginal gyrus (SMG) in 3 (19%), left RA in 2 (13%), left SMG in 2 (13%), bilateral RA in 3 (19%), multiple anatomical locations in 2 (13%). The age at epilepsy onset had the strongest prognostic effect, and full-scale intelligence quotient was relatively less-affected if the cluster was found on the SMG (β = 14.7, p = 0.031). Cases with only a right side cluster exhibited reduced impairment of perceptual organization compared with those with only a left side cluster or bilateral clusters (β = 17.48, p = 0.02). In 12 patients, long-term intellectual prognosis was evaluated, and was associated with intellectual level at the period of ECSWS diagnosis.

CONCLUSION

In non-lesional ECSWS, the relationship between epileptic focus and cognitive deficits differs from that observed in adults. Rather, it is similar to epilepsies associated with congenital or early infantile brain insults, in that the left epileptic foci in right-handed patients were associated with lower non-verbal functions. Future studies are required to determine the role of plasticity of the immature brain in driving these differences.

Ictal source imaging and electroclinical correlation in self-limited epilepsy with centrotemporal spikes

PURPOSE

To elucidate the localization of ictal EEG activity, and correlate it to semiological features in self-limited epilepsy with centrotemporal spikes (formerly called "benign epilepsy with centrotemporal spikes").

METHODS

We have performed ictal electric source imaging, and we analysed electroclinical correlations in three patients with self-limited epilepsy with centrotemporal spikes.

RESULTS

The source of the evolving rhythmic ictal activity (9.7-13.5Hz) localized to the operculo-insular area. The rhythmic EEG activity was time-locked to the contralateral focal motor seizure manifestation: facial rhythmic myoclonic jerks, with the same frequency as the analysed ictal rhythm. In all three patients, the seizures had fluctuating course with pauses of clinical and electrographic seizure activity, ranging from 0.4 to 7s.

CONCLUSION

Source imaging of ictal EEG activity in patients with self-limited epilepsy with centrotemporal spikes showed activation of the operculo-insular area, time-locked to the contralateral focal myoclonic jerks. Fragmented seizure dynamics, with fluctuating course, previously described as a hallmark in patients with psychogenic non-epileptic seizures, can occur in rolandic seizures.

Local and Distant Dysregulation of Synchronization Around Interictal Spikes in BECTS

Objective: High Density electroencephalography (HD EEG) is the reference non-invasive technique to investigate the dynamics of neuronal networks in Benign Epilepsy with Centro-Temporal Spikes (BECTS). Analysis of local dynamic changes surrounding Interictal Epileptic Spikes (IES) might improve our knowledge of the mechanisms that propel neurons to the hypersynchronization of IES in BECTS. Transient distant changes in the dynamics of neurons populations may also interact with neuronal networks involved in various functions that are impaired in BECTS patients.

Methods: HD EEG (64 electrodes) of eight well-characterized BECTS patients (8 males; mean age: 7.2 years, range: 5–9 years) were analyzed. Unilateral IES were selected in 6 patients. They were bilateral and independent in 2 other patients. This resulted in a total of 10 groups of IES. Time-frequency analysis was performed on HD EEG epochs around the peak of the IES (±1000 ms), including phase-locked and non-phase-locked activities to the IES. The time frequency analyses were calculated for the frequencies between 4 and 200 Hz.

Results: Time-frequency analysis revealed two patterns of dysregulation of the synchronization between neuronal networks preceding and following hypersynchronization of interictal spikes (±400 ms) in the epileptogenic zone. Dysregulation consists of either desynchronization (n = 6) or oscillating synchronization (n = 4) (4–50 Hz) surrounding the IES. The 2 patients with bilateral IES exhibited only local desynchronization whatever the IES considered. Distant desynchronization in low frequencies within the same window occurs simultaneously in bilateral frontal, temporal and occipital areas (n = 7).

Significance: Using time-frequency analysis of HD EEG data in a well-defined population of BECTS, we demonstrated repeated complex changes in the dynamics of neuronal networks not only during, but also, before and after the IES. In the epileptogenic zone, our results found more complex reorganization of the local network than initially thought. In line with previous results obtained at a microscopic or macroscopic level, these changes suggested the variability strategies of neuronal assemblies to raise IES. Distant changes from the epileptogenic zone in desynchronization observed in the same time window suggested interactions between larger embedded networks and opened new avenues about their possible role in the underlying mechanism leading to cognitive deficits.

Magnetoencephalography localizing spike sources of atypical benign partial epilepsy

RATIONALE

Atypical benign partial epilepsy (ABPE) is characterized by centro-temporal electroencephalography (EEG) spikes, continuous spike and waves during sleep (CSWS), and multiple seizure types including epileptic negative myoclonus (ENM), but not tonic seizures. This study evaluated the localization of magnetoencephalography (MEG) spike sources (MEGSSs) to investigate the clinical features and mechanism underlying ABPE.

METHODS

We retrospectively analyzed seizure profiles, scalp video EEG (VEEG) and MEG in ABPE patients.

RESULTS

Eighteen ABPE patients were identified (nine girls and nine boys). Seizure onset ranged from 1.3 to 8.8years (median, 2.9years). Initial seizures consisted of focal motor seizures (15 patients) and absences/atypical absences (3). Seventeen patients had multiple seizure types including drop attacks (16), focal motor seizures (16), ENM (14), absences/atypical absences (11) and focal myoclonic seizures (10). VEEG showed centro-temporal spikes and CSWS in all patients. Magnetic resonance imaging (MRI) was reported as normal in all patients. MEGSSs were localized over the following regions: both Rolandic and sylvian (8), peri-sylvian (5), peri-Rolandic (4), parieto-occipital (1), bilateral (10) and unilateral (8). All patients were on more than two antiepileptic medications. ENM and absences/atypical absences were controlled in 14 patients treated with adjunctive ethosuximide.

CONCLUSION

MEG localized the source of centro-temporal spikes and CSWS in the Rolandic-sylvian regions. Centro-temporal spikes, Rolandic-sylvian spike sources and focal motor seizures are evidence that ABPE presents with Rolandic-sylvian onset seizures. ABPE is therefore a unique, age-related and localization-related epilepsy with a Rolandic-sylvian epileptic focus plus possible thalamo-cortical epileptic networks in the developing brain of children.

Diagnosis and management of epileptic encephalopathies in children

Epileptic encephalopathies refer to a group of disorders in which the unremitting epileptic activity contributes to severe cognitive and behavioral impairments above and beyond what might be expected from the underlying pathology alone, and these can worsen over time leading to progressive cerebral dysfunction. Several syndromes have been described based on their electroclinical features (age of onset, seizure type, and EEG pattern). This review briefly describes the clinical evaluation and management of commonly encountered epileptic encephalopathies in children.

Acquired opercular epilepsy with oromotor dysfunction: magnetoencephalographic analysis and efficacy of corticosteroid therapy

The authors describe herein the magnetoencephalographic findings and long-term outcome of a girl with acquired opercular epilepsy with oromotor dysfunction. She presented with brief episodes of unconsciousness, tremulous movements of the upper limbs, and negative myoclonus, in addition to convulsive seizures. She also had prolonged episodes of dysarthria and oral motor dysfunction, a gradual decrease in speech output, impairment of finger movements, and deterioration in cognitive performance over several years. Her electroencephalography (EEG) recordings showed notable continuous sharp or sharp-slow discharges during sleep. Brain magnetic resonance images revealed no structural anomalies. Magnetoencephalographic analysis showed broadly distributed epileptic foci around the sylvian fissure, including a secondary source, explaining the specific prolonged neurological dysfunction. Antiepileptic drugs could control her seizures; however, they did not improve the other neurological symptoms or epileptiform discharge on EEG. Administration of low-dose prednisolone over a long period was effective for improving the neurological impairments of this patient.

Somatotopic distribution of peri-rolandic spikes may predict prognosis in pediatric-onset epilepsy with sensorimotor seizures

OBJECTIVE

Peri-rolandic spikes are typically seen in benign childhood epilepsy with centro-temporal spikes. However, some cases of epilepsy with peri-rolandic spikes manifest with medical intractability or cognitive dysfunction. The present study evaluated whether spike source localization is predictive of different prognosis of epilepsy and/or cognitive function.

METHODS

The localization of peri-rolandic spikes was compared between 6 patients whose seizure remitted under age of 15 years with no cognitive impairment (benign group) and 6 patients with either intractable epilepsy or cognitive dysfunction (non-benign group). The sources of epileptic spikes were approximated by the single equivalent current dipole (ECD) model using whole-head magnetoencephalography.

RESULTS

The spike locations in the benign group were significantly lateral (14.8±5.3 versus 5.3±3.3 mm, p<0.05), anterior (11.6±2.1 versus 3.7±4.8 mm, p<0.01), and inferior (27.7±3.6 versus 12.0±10.0 mm, p<0.01) to those in the non-benign group. Seizures tended to involve the laryngo-pharyngo-oro-facial area in the benign group and the facial-hand-foot area in the non-benign group.

CONCLUSION

The clear difference in spike dipole location between benign group and non-benign groups.

SIGNIFICANCE

Spike localization may be useful for predicting prognosis in epilepsy with sensorimotor seizures and spikes along with central sulcus.

Hemispheric lateralization in benign focal epilepsy in childhood with centrotemporal spikes (BECTS)

Benign focal epilepsy in childhood with centrotemporal spikes (BECTS) is one of the most common forms of epilepsy. In adults there is a higher percentage of lateralized epileptic discharges in the left cerebral hemisphere; however, in children this pattern does not seem to have the same distribution. The objective of this study was to evaluate the lateralization of interictal spikes in children with BECTS in relation to the sex of the child and the age of onset of epilepsy. We studied the electroencephalograms (EEGs) of 114 children with a clinical diagnosis of BECTS according to ILAE. The results obtained from two EEGs, performed at intervals of 6 and 12 months, were correlated with the age of onset of the epileptic seizures and the sex of the child. There was no association between the onset of epileptic seizures and the age of the child (p=0.461). When we analyzed the relationship between laterality and sex we did not observe any difference in the first EEG (p = 0.767) results; however, in the results of the second EEG there was a difference (p = 0.002). In males, left and bilateral interictal spikes were predominant, and in females the right hemisphere showed predominant spikes and there were continuous spike-and-wave discharges during slow sleep (CSWSS). The analysis between laterality and a child's age did not show predominant interictal spikes in the hemispheres, except in males where there were predominant multifocal and generalized spikes, but not lateralization (p=0.011). The conclusion was that in BECTS the lateralization of interictal spikes was not consistent as described in adult patients, but there was a slight left hemispheric predominance in boys and right hemispheric predominance in girls.

Clinical utility of current-generation dipole modelling of scalp EEG

OBJECTIVE

To investigate the clinical utility of current-generation dipole modelling of scalp EEG in focal epilepsies seen commonly in clinical practice.

METHODS

Scalp EEG recordings from 10 patients with focal epilepsy, five with Benign Focal Epilepsy of Childhood (BFEC) and five with Mesial Temporal Lobe Epilepsy (MTLE), were used for interictal spike dipole modelling using Scan 4.3 and CURRY 5.0. Optimum modelling parameters for EEG source localisation (ESL) were sought by the step-wise application of various volume conductor (forward) and dipole (inverse) models. Best-fit ESL solutions (highest explained forward-fit to measured data variance) were used to characterise best-fit forward and inverse models, regularisation effect, additional electrode effect, single-to-single spike and single-to-averaged spike variability, and intra- and inter-operator concordance. Inter-parameter relationships were examined. Computation times and interface problems were recorded.

RESULTS

For both BFEC and MTLE, the best-fit forward model was the finite element method interpolated (FEMi) model, while the best-fit single dipole models were the rotating non-regularised and the moving regularised models. When combined, these forward-inverse models appeared to offer clinically meaningful ESL results when referenced to an averaged cortex overlay, best-fit dipoles localising to the central fissure region in BFEC and to the basolateral temporal region in MTLE. Single-to-single spike and single-to-averaged spike measures of concordance for dipole location and orientation were stronger for BFEC versus MTLE. The use of an additional pair of inferior temporal electrodes in MTLE directed best-fit dipoles towards the basomesial temporal region. Inverse correlations were noted between unexplained variance (RD) and dipole strength (Amp), RD and signal to noise ratio (SNR), and SNR and confidence ellipsoid (CE) volume. Intra- and inter-operator levels of agreement were relatively robust for dipole location and orientation. Technical problems were infrequent and modelling operations were performed within 5min.

CONCLUSIONS

The optimal forward-inverse single dipole modelling set-up for BFEC and MTLE interictal spike analysis is the FEMi model using the combination of rotating non-regularised and moving regularised dipoles. Dipole modelling of single spikes characterises best-fit dipole location and orientation more reliably in BFEC than in MTLE for which spike averaging is recommended.

SIGNIFICANCE

The clinical utility of dipole modelling in two common forms of focal epilepsy strengthens the case for its place in the routine clinical work-up of patients with localisation-related epilepsy syndromes.

Benign epileptiform discharges in Rolandic region with mesial temporal lobe epilepsy: MEG, scalp and intracranial EEG features

AIM OF THE STUDY

To report benign epileptiform discharges (BEDs) in the Rolandic region, coexisting in a pediatric patient with intractable localization-related epilepsy, secondary to hippocampal sclerosis.

METHODS

We describe the clinical features, MRI, scalp video EEG, magnetoencephalography (MEG) and intracranial video EEG findings, and surgical outcome in a 9-year-old boy with BEDs and intractable complex partial seizures.

RESULTS

MRI showed left hippocampal sclerosis. Scalp video EEG interictally demonstrated left temporal spike and sharply contoured slow waves, and right fronto-centro-temporal spike and waves. Ictal scalp video EEG showed left temporal rhythmic sharp waves after the clinical onset of epigastric aura, followed by staring. MEG showed interictal dipoles in the bilateral Rolandic regions with a uniform orientation and right hemispheric predominance. Intracranial video EEG, with bilateral mesial temporal depth and fronto-temporo-parietal strip electrodes, interictally showed polyspikes and slow waves with superimposed low-amplitude fast waves in the left mesial and posterior lateral temporal regions, and spike and waves in the bilateral fronto-parietal regions. Ictal onset was marked by low-amplitude fast waves in the left mesial and posterior lateral temporal regions. He underwent left anterior temporal lobectomy with hippocampectomy. Pathology was hippocampal sclerosis. Predominant right fronto-centro-temporal spike and waves and MEG right Rolandic dipoles persisted after surgery. He was seizure-free 14 months after surgery.

CONCLUSION

This is the first report on MEG and intracranial video EEG features of BEDs in the Rolandic region, coexisting with hippocampal sclerosis. Persistence of contralateral benign MEG Rolandic dipoles after surgery indicates that BEDs are coincidental in mesial temporal lobe epilepsy. MEG identified Rolandic dipoles, although was unable to localize the deep and focal epileptogenic dipoles from the hippocampal sclerosis.

Magnetoencephalography in epilepsy: tailoring interpretation and making inferences

Although the ability of magnetoencephalography (MEG) to detect epileptiform discharges noninvasively has long been known, only recently has it become a common tool in clinical settings. Whether MEG or electroencephalography (EEG) is superior has been controversial; MEG has a theoretic edge over EEG for precise localization, but EEG has many practical advantages. Experience has shown that they often provide different and complementary information. Although the results of careful MEG analysis can be quite precise, MEG interpretation, like that of EEG, is partly subjective and reader dependent. Therefore, the appearance of well-defined foci on MEG should not reflexively be regarded as conclusive, but weighed by judgment, experience, and an understanding of the assumptions and behavior of the localization model. We review selected studies in the past 2 years that are relevant to epilepsy. In particular, studies are described that provide insights into MEG's relation to EEG, its contribution to preoperative decision making, its application to benign Rolandic epilepsy, and analysis of secondary generalization.

Spike orientation may predict epileptogenic side across cerebral sulci containing the estimated equivalent dipole

OBJECTIVE

To evaluate whether the orientation of interictal spikes, localized in major sulci by magnetoencephalography (MEG), predicts the epileptogenic side of the sulcal wall.

METHODS

Sixteen epilepsy patients were analyzed in whom equivalent current dipoles (ECDs) of MEG spikes were localized on the central (four patients), interhemispheric (4), or sylvian fissure (8); and the epileptogenic side across the sulci had been confirmed by seizure semiology, structural lesions, or intracranial electroencephalography (EEG). ECD was classified as epileptogenic side or normal side oriented and correlated to the scalp EEG map.

RESULTS

All central (n=50) and interhemispheric (n=83) spike ECDs were oriented toward the epileptogenic side at peak latency. In scalp EEG, 91% of the spikes showed radial pattern of broad negativity above the sulcus whereas 9% showed tangential pattern with positive maximum above the epileptogenic side. Sylvian spikes were only found in patients with temporal lobe epilepsy (TLE). In sylvian spikes (n=220), 73% of ECDs were oriented toward the epileptogenic side, whereas 27% were oriented toward the normal side.

CONCLUSIONS

In central and interhemispheric spikes, epileptogenic side cortex may be gross surface negative through the sulcal wall to the adjacent gyrus. Inconsistent orientation of the sylvian spikes suggests a complex pattern of spike propagation in TLE.

SIGNIFICANCE

ECD orientation of central and interhemispheric spikes in MEG may predict the epileptogenic side.

Bilateral oscillations for lateralized spikes in benign rolandic epilepsy

PURPOSES

To elucidate the oscillatory dynamics with respect to interictal spike occurrence in benign rolandic epilepsy (BRE).

METHODS

Using a whole-scalp magnetoencephalography (MEG), we recorded scalp EEG and MEG signals in 10 BRE patients (age 8-12 years) and visually identified unilateral interictal spikes that were simultaneously present on both EEG and MEG channels. We obtained the peak timing of individual spike complex based on MEG single-dipole modeling, and then applied wavelet transform to analyze the time-frequency components of corresponding MEG signals with respect to spike occurrence.

RESULTS

In the hemisphere with time-domain spike waveforms, we identified a clear increase of 0.5-40 Hz activity around the spike peak, most prominent at alpha band (8-13 Hz). Notably, at the approximate timing we also observed an increase in 0.5-25 Hz oscillations over the homotopic area in the other hemisphere where no spike signals were found.

CONCLUSIONS

Our results indicate bilateral increases in 0.5-25 Hz oscillations during unilateral spike formation in BRE patients. By using wavelet transform analysis, one could be able to detect some irritative feature that would in visual analysis remain undetected.