Abstracts

RATIONALE: Recent studies have shown nonlinear EEG analysis to be useful for detecting pre/interictal and permanent changes of neuronal synchronization in epilepsy patients. We were interested whether characteristic changes of EEG power, synchronization, and complexity can also be found in the focal EEG during amygdala kindling in rats, a model of human temporal lobe epilepsy. The advantage of this model is the possibility to record at various stages before and after seizures during the stepwise progression of limbic epileptogenesis. METHODS: Eight female Wistar rats were implanted with a bipolar chronic stimulation/recording electrode into the right basolateral amygdala. After two weeks, the rats were daily stimulated (500 A, 1 ms pulses, 50 Hz for 1 s) which elicited initially limbic focal and subsequently secondary generalized seizures. The unipolar EEG of the amygdala was recorded versus an indifferent screw electrode in the contralateral parietal bone for 30 min before and after each seizure. Using a moving-window approach, spectral power, complexity (measured by an effective correlation dimension), and synchronization (measured by the mean phase coherence) were determined. RESULTS: The immediate effect of the first kindling stimulation was an increase in EEG synchronization in most rats. Evaluation of changes in amygdala EEG parameters after kindling has progressed to secondary generalized seizures, i.e. after nine daily stimulations, revealed a significant increase in power and a decrease in complexity after the kindled seizure. In these kindled rats a significant increase in EEG synchronization was found before the kindling stimulation, indicating that kindling caused a permanent change of EEG activity. CONCLUSIONS: Different measures from nonlinear time series analysis of the focal EEG provide supplementary information about different states of neuronal synchronization during amygdala kindling. Focal seizures increase neuronal synchronization which becomes permanent during kindling acquisition. Fully kindled seizures increase power and decrease complexity of the EEG which may be the basis of the postictal depression after these seizures.