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Synchronized Minima in ECoG Power at Frequencies Between Beta-Gamma Oscillations Disclose Cortical Singularities in Cognition


Electrocorticogram (ECoG) data of trained rabbits are analyzed to identify neural correlates of cognition. Previous work indicated long periods of large-scale synchronization of cortical activity, punctuated intermittently by brief desynchronization events. The actual timing of the synchronization events generally depends on the analyzed frequency band, from alpha to high gamma. Here we present the surprising experimental indications that the desynchronization events may synchronize briefly over a wide range of frequencies during a singular event of cognition. The observed synchronization of desynchronization (SOD) effect has significant invariance over broad frequencies. This observation is in line with the expected scale-free behavior of critical brain dynamics. To quantify the observed SOD phenomenon, we analyze information-theoretic measures based on the con- cept of pragmatic information, to complement the Shannon entropy index. We demonstrate the benefit of the new indices in the analysis and detection of phase transitions and possible desynchronization windows in time domain. The results are interpreted in terms of a dynamical system approach to brains operating in a domain of criticality. 

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