Spectral power of 1-4 Hz frequency in the ictal phase of childhood absence epilepsy.

The ictal EEG of childhood absence epilepsy is characterized by short duration bursts of generalized 3-Hz spike-wave discharges, which are widely considered to be symmetric and synchronous. The purpose of this study was to investigate this assertion by studying the topography and spectral power of these discharges. The sample consisted of 7 subjects aged 4 to 9 years who had been diagnosed with childhood absence epilepsy by video-EEG monitoring. Computational EEG analysis was performed focusing on the slow-wave (1-4 Hz) component of the ictal EEG. We compared the spectral power of this slow-wave component in three brain regions (frontocentral, centroparietal, and parieto-occipital) and contrasted the spectral power of left and right fronto-central areas. Although five of seven subjects showed marked frontal dominance of spectral slow-wave power, two subjects had a different pattern characterized by a more diffuse anterior-posterior distribution. Three patterns of spectral power laterality in the frontocentral region were observed: left dominant, equivocal, and right dominant. Each subject demonstrated the same pattern throughout his or her seizures (three to five ictal events) during video-EEG monitoring. These findings suggest that computational EEG may be useful for discerning subtle differences in the distribution of ictal waveforms. These observations also bolster the new ILAE definition of generalized seizures, suggesting that some so-called generalized seizures are not truly generalized but that they instead rapidly engage bilaterally distributed networks with clear asymmetries of scalp electrical discharges.