Top-down modulation of memory traces reflected by gamma- theta-, and alpha-band oscillations in human-EEG and MEG

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In the present research project, we intend to investigate how different brain regions communicate during memory encoding and retrieval. The temporal synchronization of neuronal activation plays a key role for the communication between populations of neurons. Therefore, synchronization can also be regarded as a key mechanism for the integration of cognitive functions which are represented in spatially distributed cortical areas. In the first part of the project we tested the hypothesis if synchronized activity in the gammaband range (> 30 Hz) reflects the activation of memory traces. This assumption has been confirmed. Moreover, our results indicated that in the context of a memory task, gammaband synchronizations covary with oscillations in the thetaband range. Thetaband oscillations presumably reflect executive processes. Consequently, in the second part of the project we want to investigate in detail, how the activation of memory traces is modulated by higher cognitive functions. We focus on the analysis of theta- and alphaband oscillations which are discussed as correlates of executive control and working memory processes. The intended investigation of the interplay between gamma-, theta- and alphaband oscillations allows for a comprehensive analysis of mnemonic sub-processes contributing to long-term and working memory. Our findings might, amongst others, resolve the controversy to what extent both memory systems are realized as distinct cortical modules or as a unified system. To characterize the dynamic interactions of the underlying sub-processes, coupling between frequency bands need to be quantified directly. Therefore, the implementation and development of cross-frequency coupling analysis methods constitute vital aspects of the project.