Evidence for slow brain waves: a dynamical approach.

Various techniques of non-linear dynamics have been applied with success to EEG data and have provided a new insight into brain dynamics. Among these the 'recurrence plot' is a powerful tool for revealing the presence of drift or periodicities and is easily obtained in the framework of a non-linear dynamical analysis. When this analysis is applied to the EEG recorded from a patient suffering from Creutzfeldt-Jakob disease one observes the presence of slow periodicities of the order of 58 sec. We suggest that the recurrence plots are powerful tools for discovering hidden periodicities of EEG as well as the degree of stationarity of brain activity.