TOPOGRAPHIC EEG MAPPING OF 3 S SPIKE-AND-WAVE COMPLEXES DURING ABSENCE SEIZURES/

Topographic color mapping has recently been introduced for the study o f 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 curing the 2 sec preceding the 3/s sw bursts. An increase in delta and theta ban ds 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. I n 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 radial ly oriented dipole. We conclude that EEG changes can be detected befor e 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 se izure; moreover a frontal cortical mechanism seems to be prevalently a ctive at the beginning of the seizure, which is soon captured by a cor tico-subcortical process as the attack progresses.