How to construct a micro state-based alphabet for evaluating information processing in time

Cognitive processes are highly dynamic processes concatenating different components of human thinking successively or parallel in time. Thereby, different cortical networks are generated, transient or stable in time. One important integration mechanism between different cortical sites is the synchronization of electrical oscillations of neural ensembles. Prior studies have shown that instantaneous EEG coherence analysis is a useful tool to unhide transient synchronization phenomena (see e.g. [Krause et al., 1998; Miltner et al., 1999; Schack et al., 1999a, 1999b]). In those studies instantaneous coherence was investigated for selected short time intervals, respectively, specific time parameters of instantaneous coherence were examined. The present study proposes a method for the evaluation of the whole cognitive process on the basis of instantaneous coherence without loss of time and process information. To this purpose prototypical microstates of synchronous oscillations are constructed. Their temporal, sequential and topographical properties reflect the underlying process of the dynamic activation and deactivation of neuronal networks during information processing. The sequence of microstates may be understood as the orderly arrangement of words of an alphabet in the correspondent thinking process. The presented method is applied to an event-related cognitive task of comparing categorization processes, pattern comparison, and to an irreproducible long task when solving; mathematical problems. In both cases we obtain detailed information about temporal structures and strategies of human thinking.