[The propagation of acetylcholine-induced seizures (author's transl)]

Acetylcholine (ACh) injected into the cortex induces epileptic seizures which spread very slowly, with a propagation speed of some millimeters per minute over the cortex. To study this propagation mechanism the ECoG recorded with two rows of equally spaced electrodes, one row on the homolateral the other on the contralateral hemisphere, was analysed using correlation techniques and spectral analytical methods. Rabbits were used as experimental animals. If a cortical area is involved in the seizure of rhythmic fast and low activity of about 30 Hz is observed. The frequency decreases discontinuously and simultaneously the amplitudes increase. After one or more seconds the activity seems to stabilize showing a tonic pattern of about 9 Hz but a few seconds later this tonic pattern is replaced by an irregular seizure activity. This mechanism was found for the spreading of the primary focus as well as for the spreading of the mirror focus on the contralateral hemisphere which occurs about 2 hours after the injection of ACh. The analysis of the approximately 9 Hz tonic period yielded the following results: at the beginning, the 9 Hz activity of the cortical area already involved leads the activity of the adjacent area which is going to be involved. High coherences were found between both areas during this state. Then the coherence decrease, indicating an uncoupling of the two areas. The subsequent increase of coherence indicates a renewed coupling, but now the newly involved area is leading. This was found by correlation and phase analysis. From these results it can be concluded that the propagation of such seizures is based on a stepwise propagation of an active focus and that the propagation is strongly correlated with certain graphoelements and rhythms.