title: Time-frequency characterization of interdependencies in nonstationary signals: application to epileptic EEG.
abstract: For the past decades, numerous works have been dedicated to the development of signal processing methods aimed at measuring the degree of association between electroencephalographic (EEG) signals. This interdependency parameter, which may be defined in various ways, is often used to characterize a functional coupling between different brain structures or regions during either normal or pathological processes. In this paper, we focus on the time-frequency characterization of the interdependency between signals. Particularly, we propose a novel estimator of the linear relationship between nonstationary signals based on the cross correlation of narrow band filtered signals. This estimator is compared to a more classical estimator based on the coherence function. In a simulation framework, results show that it may exhibit better statistical performances (bias and variance or mean square error) when a priori knowledge about time delay between signals is available. On real data (intracerebral EEG signals), results show that this estimator may also enhance the readability of the time-frequency representation of relationship and, thus, can improve the interpretation of nonstationary interdependencies in EEG signals. Finally, we illustrate the importance of characterizing the relationship in both time and frequency domains by comparing with frequency-independent methods (linear and nonlinear).
authors.affiliation: Laboratoire Traitement du Signal et de L'Image, INERM U 642, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes, France.
authors.forename: Karim
authors.initials: K
authors.lastname: Ansari-Asl
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Bellanger
authors.forename: Fabrice
authors.initials: F
authors.lastname: Bartolomei
authors.forename: Fabrice
authors.initials: F
authors.lastname: Wendling
authors.forename: Lotfi
authors.initials: L
authors.lastname: Senhadji
mesh_terms: D000465:Algorithms; D001921:Brain / Q000503:physiopathology*; D003198:Computer Simulation; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology*; D006801:Humans; D008959:Models, Neurological; D015233:Models, Statistical; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013269:Stochastic Processes