Quantification of transient quadratic phase couplings within EEG burst patterns in sedated patients during electroencephalic burst-suppression period

The time dynamics of the quadratic phase coupling within burst patterns dur ing electroencephalic burst-suppression has been quantified. It can be show n that a transient quadratic phase coupling (QPC) exists between the freque ncy ranges 0 to 2.5 and 3 to 7.5 Hz and between the frequency ranges 0 to 2 .5 and 8 to 12 Hz. The QPC can be explained by an amplitude modulation, whe re the slow rhythm modulates the rhythmic activities with a higher frequenc y. By means of time-variant bicoherence analysis, a strong phase-locking be tween the modulating and the modulated component can be identified. The pha se-locking is demonstrable within the first 250 ms after the burst onset an d comes up to the maximum between 750 and 1250 ms. The effect is maintained over the whole first part of the burst (2 a) with a decreasing tendency af ter 1250 ms. All these effects cannot be found in the LEG before entering t he burst suppression period (BSP). The transient coupling phenomena in the EEG bursts during BSP can be regarded as indicators for short-term interrel ations between the underlying electrophysiologic processes. (C) 2000 Elsevi er Science Ltd. Published by Editions scientifiques et medicales Elsevier S AS.