Transverse topographical analysis of petit mal discharges: diagnostical and pathogenic implications

Independent component analysis of generalized spike-and-wave discharges: primary versus secondary bilateral synchrony

OBJECTIVE

To differentiate between primary and secondary bilateral synchrony (PBS and SBS, respectively) in generalized spike-and-wave discharges (GSWD), we applied independent component analysis (ICA) to GSWD, and analyzed the characteristic patterns of independent components.

METHODS

EEGs from 19 patients with GSWD (9 PBS patients, 10 SBS patients) were studied. Thirty GSWD epochs were selected and concatenated to construct an EEG data matrix that was subjected to ICA. Selected independent components were localized by mapping them on a spherical model of the head by means of brain electrical source analysis (BESA) to define dipole sources.

RESULTS

Epileptic components of GSWD were clearly separated by the ICA algorithm in all patients. Between one and three components per patient were responsible for GSWD. In PBS patients, 70.6% of the independent components had dipole sources within the dorsolateral frontal region, and 56.5% of the independent components in SBS patients were within the medial frontal region (P=0.012). The orientation of all of the independent components in PBS patients was radial, whereas 47.8% of the independent components in SBS patients were tangential; this difference was statistically significant (P=0.001).

CONCLUSIONS

Spatiotemporal decomposition of GSWD by using ICA might be helpful for differentiating SBS from PBS.

SIGNIFICANCE

The localization of the dipole sources of the independent components may provide insight into the pathophysiological origins of GSWD.

Source analysis of polyspike and wave complexes in juvenile myoclonic epilepsy

We applied dipole modeling and brain distributed source analysis to find current sources comprising spikes and slow waves of polyspike and wave complexes (PSWC) in patients with juvenile myoclonic epilepsy (JME). The dipoles were localized in frontal, parietal and temporal lobes. The frontal dipoles were clustered in the frontal medial gyrus and fronto-orbital region. A midsagittal frontal current source was observed using brain distributed source analysis in all patients. When the slow wave was analyzed, multiple sources in different cortical regions were detected using dipole modeling and brain distributed analysis. These results show pre-frontal medial current sources corresponding to spikes and many diffuse sources in cortical regions corresponding to wave components of PSWC in patients with JME.

Decomposition and mapping of generalized spike-wave complexes

OBJECTIVE

To delineate more precisely the electrical fields of spikes versus waves during absence seizures.

METHODS

Five children with 25 absence seizures were investigated with an expanded electrode array. Spikes were separated from waves by appropriate filtering and current source density maps were obtained from different portions of the waves as well as spikes. In order to detect commonalities for spread of activity, averaging of the complexes was also carried out.

RESULTS

The anterior head regions (prefrontal and fronto-polar) show independent activity from the posterior ones (parieto-occipital) for spikes as well as waves. Voltage maps give a simplified and therefore misleading picture. The complexity of the process and propagation of events is best appreciated when current source densities (CSD) are mapped and several head views are available. Spike 1 becomes clearly visible upon filtering, even when it is not apparent from raw tracings, and can be mapped.

CONCLUSIONS

Future topographic investigations of the SW complex should utilize CSD maps rather than rely entirely on voltages. This applies also to seemingly focal spikes--especially in children--in order to differentiate them from a partial expression of a generalized seizure tendency.

Modern electroencephalography: its role in epilepsy management

Epilepsy is the area in which electroencephalography is probably of greatest potential clinical value, and yet is most abused. In general, the sensitivity of the waking interictal EEG for detecting epilepsy and its specificity for distinguishing epilepsy from other episodic disorders are both very limited, and routine examination for diagnostic screening or follow up is of little value. However, as this review attempts to demonstrate, EEG is of crucial importance for answering specific, clearly defined questions which commonly arise in the management of seizure disorders, especially so, when non-routine and if necessary complex investigations are undertaken, to address the problems of individual patients.

Topographic EEG mapping of 3/s spike-and-wave complexes during absence seizures

Topographic color mapping has recently been introduced for the study of ictal EEG manifestations of absences. We recorded 2-4 3/s spike-and-wave (sw) bursts in 12 patients with absence epilepsy, and performed a spectral analysis of the EEG under baseline conditions and during the 2 sec preceding the 3/s sw bursts. An increase in delta and theta bands was found in preseizure conditions. Moreover, the serial mapping of the sw complexes showed a different field distribution of the various components when the first sw was compared with the subsequent ones. In particular, the negative peak of the spike was mainly frontal during the first complex, with a tangentially oriented dipole, but it became better represented over the midline in the following sw, with a radially oriented dipole. We conclude that EEG changes can be detected before the onset of 3/s sw activity in absences, and that they are probably related to the strong inhibitory mechanisms acting in this type of seizure; moreover a frontal cortical mechanism seems to be prevalently active at the beginning of the seizure, which is soon captured by a cortico-subcortical process as the attack progresses.

Simultaneous EEG-VTR and transverse topographical analyses of absence seizures in children. Some prognostic implications

The clinical symptoms and electroencephalographic (EEG) features of typical absence seizures, including transverse topographical analysis (TTA), were studied retrospectively using a simultaneous EEG-VTR system in 36 children aged between 3 and 17 years. Complex absences were more common than simple, and oral automatisms were the most frequent complex symptoms. Occurrence of complex symptoms was directly proportional to the length of seizures. There was no association between lateral TTA type and simple absences. Prognosis was favorable in patients with long seizure duration (P < 0.01), bilaterally synchronous monomorphic spike-waves throughout the seizure discharges (BSMTSD) (P < 0.005) and lateral TTA type (P < 0.05). Two different mechanisms of origin for BSMTSD/non-BSMTSD and lateral/non-lateral TTA types are probably responsible for the difference in prognosis. Favorable prognosis in patients with long seizures is discussed in relation to the duration of the illness. EEGs with BSMTSD and lateral TTA type may indicate a favorable prognosis in children with absence seizures.

Neurosurgical applications of topographic mapping

Sophisticated spectral analysis and mapping of the EEG with computer techniques provides objective and reliable diagnostic information, which is superior to that obtained by naked-eye observation, even by experienced clinicians. In our department, a topographic system was introduced as one of major adjuncts to EEG examination in 1980, and we devised our own software (dynamic topography, compound dynamic topography, deviation ratio topography) to facilitate its clinical application. Topographic mapping is applied to assessment of the dominant hemisphere, evaluation after medical and surgical treatment, spatial localization of epileptic foci, and intraoperative monitoring for cerebral hypoperfusion. Besides these surgical applications, topographic analysis has contributed to human neurophysiology, for instance in determining the participation of the dentatethalamic tract in movement-related cortical potentials. Our experience of the neurosurgical and neurophysiological applications of topographic mapping will be presented.

Topographical evolution of spike-wave complexes

Computer-generated 3-dimensional field potential maps of spike-wave complexes from two 4 X 4 electrode grids on the scalp were studied. A visual analysis of these field maps throughout the spike-wave evolution permitted quantification of the spike, trough and slow wave components in terms of distribution, origin and propagation. In addition, a more objective morphological analyzer also quantified the discriptive parameters of distribution, origin and propagation for the spike component of the patients' spike-wave complexes. We found that field distributions of spikes differed from that of waves. Succeeding positive troughs evolved more symmetrically than did spikes but less than ensuing negative waves. Negative waves were more diffuse, more symmetrical in evolution, and more posteriorly centred than either spikes or troughs. Unlike the troughs and slow waves whose fields tended to remain stationary during their evolution, spikes always moved from their points of origin. Spikes originated at the most lateral points of the grids and propagated laterally and anteriorly in one of two ways: a simultaneous origin at both lateral positions, then propagation toward the midline, and then usually anteriorly, a clearly unilateral origin with spread contralaterally to the homologous electrode position of the contralateral hemisphere followed again by anterior propagation. Interhemispheric lag times of spikes ranged from 0 to 25 ms with an average of 10.5 ms. Inter- and intrapatient variability was considerable. This type of analysis reveals properties of spike-wave complexes which may not be appreciated by standard paper writeout.

Primary generalised epileptic myoclonus: a frequent manifestation of minipolymyoclonus of central origin

A group of patients with myoclonus is described whose jerks are preceded by a bilaterally synchronous, frontocentrally predominant, negative cerebral potential in the EEG. This potential may be a slow wave with variable timing in relation to EMG bursts, and in this circumstance the muscle jerks are usually small amplitude and multifocal ("minipolymyoclonus"). The cerebral negativity can also be shorter in duration and time-locked to limb jerks, which are larger in amplitude and more widespread. We propose that the physiology of this distinct form of myoclonus is similar to that of primary generalised epilepsy.