[Analysis of the extension of epileptic discharges in the animal model]

The study was aimed at the enlightenment of intracortical spreading mechanisms in focal epileptic seizures produced by local application of Acetylcholine. Experiments were made in rabbits. Epi- and intracortical seizure potentials were recorded simultaneously with special electrodes. The recorded signals were analysed using computer aided methods. The results show, that the spreading of the pathological events does not take place continuously but by successive generation of "active zones" independent of the original focus produced by Acetylcholine. In the epicortical recordings, the development of a new focus is indicated by a functional uncoupling between the superficial layers of the cortical area to be involved and the momentary active focus. This functional uncoupling is due to an activation of the middle cortical layers of this area by the focus. As a first sign, high frequent potentials can be observed in the middle cortical layers accompanied by an amplitude decrease in the superficial layers. In the further development high negative discharges appear in the middle cortical layers which lead to characteristic surface positive potentials. This phase indicates that a new focus has developed, i.e. the discharges are no longer triggered by the previous focus. These processes continue as long as inactive cortical areas are available. From the obtained results it can be assumed with high probability that in contrast to previous assumptions the generation of a new epileptic focus is not initiated via superficial axon collaterals but that other cortical connections must be responsible. Additionally, it has to be taken into account that extra- and/or intracellular changes of ion concentrations as a consequence of the massive synaptic bombardment may be responsible for the independent discharges in the focus.