The influence of stimulation parameters on the relative phase clustering index

For most people suffering from epilepsy the unpredictability of their spontaneous seizures considerably contributes to the burden of their disease. Therefore active and passive seizure prediction methods have been investigated since the 1970s. Among them, the relative phase clustering index (rPCI) has been reported to be a promising stimulation based technique that offers the possibility to localize the seizure onset zone as well as the likelihood for a seizure occurrence within different time ranges. The adaptation of this measurement to animal models of epilepsy would not only offer the possibility to realize and test closed-loop setups based on identification of a preictal period; it would also provide the possibility to test therapeutic paradigms in a much faster and more efficient way. We investigated the transferability of the concept of the rPCI to the epilepsy model of the rat. Adaptation of stimulation parameters, especially the current amplitude, will be necessary for the application in animals, due to different electrodes as well as different anatomical sizes. Therefore, the influence of the stimulation parameters on the results of this active probing are analyzed in this study. While the amplitude and the pulse width (PWD) seem to affect the determined phase clustering index, no correlation with the frequency of test stimulus application could be proven. In the range between 1-5 μA the rPCI increased with increasing the current amplitude. Above that, it stabilized until the stimulation artifact resulted in the saturation of the amplifiers, which made the determination of the rPCI impossible. In addition, stimulation with a longer PWD resulted in higher rPCI values.