Spatio-temporal dynamics prior to neocortical XXXX : amplitude versus phase couplings.

@entity1 @entity410 @entity1315 @entity302
The mechanisms underlying the transition of brain activity toward @entity302 remain unclear. Based on nonlinear analysis of both intracranial and scalp electroencephalographic (EEG) recordings, different research groups have recently reported dynamical smooth changes in @entity302 brain activity several minutes before @entity410 onset. Such preictal states have been detected in populations of @entity1 with @entity1315 ( @entity1315 ) and, more recently, with different neocortical @entity302 (NPEs). In this paper, we are particularly interested in the spatio-temporal organization of epileptogenic networks prior to @entity410 in @entity302 . For this, we characterize the network of two @entity1 with NPE by means of two nonlinear measures of interdependencies. Since the synchronization of neuronal activity is an essential feature of the generation and propagation of @entity302 activity, we have analyzed changes in phase synchrony between EEG time series. In order to compare the phase and amplitude dynamics, we have also studied the degree of association between pairs of signals by means of a nonlinear correlation coefficient. Recent findings have suggested changes prior to @entity410 in a wideband frequency range. Instead, for the examples of this study, we report a significant decrease of synchrony in the focal area several minutes before @entity410 (>30 min in both @entity1 ) in the frequency band of 10-25 Hz mainly. Furthermore, the spatio-temporal organization of this preictal activity seems to be specifically related to this frequency band. Measures of both amplitude and phase coupling yielded similar results in narrow-band analysis. These results may open new perspectives on the mechanisms of @entity410 emergence as well as the organization of neocortical epileptogenic networks. The possibility of forecasting the onset of @entity410 has important implications for a better understanding, diagnosis and a potential treatment of the @entity302 .
