EEG Theta and Working Memory

Recent research provides converging evidence that EEG theta is particularly responsive` to working memory (WM) demands. The crucial question, however, is whether theta reflects global working memory processes in general, or more specific functions. The most consistently reported findings are that theta is related to the maintenance of information in WM and that a short lasting increase in theta can be observed during the encoding and retrieval of episodic information (regardless of modality and stimulus type). Furthermore, a long lasting increase in Fm is associated with sustained attention. There is, however, no clear evidence whether theta is involved in sensory and perceptual processes as was shown e.g., for gamma. Most interestingly, some studies indicate that gamma and theta become phase coupled during episodic processing. These findings suggest that theta may play an important role for the establishment of complex multi-dimensional` episodic codes. Although the episodic hypothesis provides a possible basis to explain most of the reviewed findings, alternative interpretations cannot be ruled out. It is argued that a better evaluation of the functional role of theta is possible only if new experimental designs are applied which are used to study implicit memory, trace strength and the influence of new semantic, meaningless and sensory information. Most interestingly, these designs which are frequently used in Cognitive Psychology, have not yet been applied to investigate the functional meaning of theta. The aim of the project is to analyze theta (together with other frequencies, particularly gamma but also alpha and delta) in experiments specially designed to dissociate episodic processes from potentially confounding factors such as e.g., attention, sensory and semantic encoding processes. A series of 9 experiments is suggested. EEG theta will be analyzed by standard methods (Spectral power; ERD/ERS; ERBP, IPB) but also by methods that allow a better time-frequency resolution, such as Gabor wavelet based power-frequency analyses. Most importantly, phase sensitive measures such as phase locking but also coherence and phase synchronization (n:n and m:n) will be used to study coherent and synchronized neural processes in distributed assemblies. The application of m:n phase synchronization serves to investigate the interesting question whether gamma oscillations - possibly reflecting perceptual encoding - are nested within theta cycles to form complex multi-dimensional` episodic codes.

Recent research provides converging evidence that EEG theta is particularly `responsive` to working memory (WM) demands. The crucial question, however, is whether theta reflects global working memory processes in general, or more specific functions. The most consistently reported findings are that theta is related to the maintenance of information in WM and that a short lasting increase in theta can be observed during the encoding and retrieval of episodic information (regardless of modality and stimulus type). Furthermore, a long lasting increase in Fm is associated with sustained attention. There is, however, no clear evidence whether theta is involved in sensory and perceptual processes as was shown e.g., for gamma. Most interestingly, some studies indicate that gamma and theta become phase coupled during episodic processing. These findings suggest that theta may play an important role for the establishment of complex `multi-dimensional` episodic codes. Although the episodic hypothesis provides a possible basis to explain most of the reviewed findings, alternative interpretations cannot be ruled out. It is argued that a better evaluation of the functional role of theta is possible only if new experimental designs are applied which are used to study implicit memory, trace strength and the influence of new semantic, meaningless and sensory information. Most interestingly, these designs which are frequently used in Cognitive Psychology, have not yet been applied to investigate the functional meaning of theta. The aim of the project is to analyze theta (together with other frequencies, particularly gamma but also alpha and delta) in experiments specially designed to dissociate episodic processes from potentially confounding factors such as e.g., attention, sensory and semantic encoding processes. A series of 9 experiments is suggested. EEG theta will be analyzed by standard methods (Spectral power; ERD/ERS; ERBP, IPB) but also by methods that allow a better time-frequency resolution, such as Gabor wavelet based power-frequency analyses. Most importantly, phase sensitive measures such as phase locking but also coherence and phase synchronization (n:n and m:n) will be used to study coherent and synchronized neural processes in distributed assemblies. The application of m:n phase synchronization serves to investigate the interesting question whether gamma oscillations - possibly reflecting perceptual encoding - are nested within theta cycles to form complex `multi-dimensional` episodic codes.