Morphology of spikes in spike-and-wave complexes

The morphology of spikes of spike-and-wave complexes from 9 patients with primary generalised epilepsy was studied from the scalp recordings of electrodes placed over their fields of maximum expression. Using a 4 x 4 grid electrode placement, selected epochs of the EEG were digitised and stored by a computer program which determined the times of the troughs and peak of the spike as well as its slope, amplitude and duration. Morphological parameters corresponding to those studied for focal spikes in other works gave similar values suggesting a close resemblance between spikes of generalised spike-and-wave complexes and focal spikes. In this study, second half-wave duration exceeded first half-wave duration and amplitudes of the second half-waves were either equal to or greater than those of the first half-waves. Our measures of slope resolved an apparent discrepancy among earlier studies: the entire first half-wave slope was usually equal to or greater than the second half-wave slope while the slopes of the upper half of the spike were usually equal or greater for the second half-wave than for the first. The first half-wave: second half-wave slope ratio was greatest at electrode positions with the maximum spike amplitude (the midline frontal electrodes), and therefore more closely resembled electrocorticogram spikes at these positions.