Comparison of event-related modulation index and traditional methods for evaluating phase-amplitude coupling using simulated brain signals

The neural mechanism of non-phase-locked EEG activity in task switching

Phase-amplitude coupling (PAC) is a well-established concept for evaluating the strength of memory coding within brain regions, and has been shown to possess the characteristic of presenting memory mechanisms. It has been demonstrated that oscillations of theta and gamma brain waves can represent the neural coding structure of memory retrieval. However, most previous studies have presented PAC-related memory mechanisms with visual modalities, and little is known about the influence of auditory stimuli. In this study, 18 participants were recruited and 36-channels electroencephalography (EEG) signals were recorded while they were performing an $n$ -back auditory working memory task. There were three experimental conditions with different levels of working memory load. Event-related phase-amplitude coupling (ERPAC) with the advantage of better temporal resolution was used to evaluate the coupling phenomenon from the reconstructed dipole brain sources. We primarily focused on independent components from the frontal and parietal regions, which were reported to be related to memory mechanisms. The results suggest that significant ERPAC was observed in both the frontal and parietal regions. In addition to the coupling between theta (4-7 Hz) and low gamma (30-40 Hz) frequency bands, pronounced high beta oscillations (20-30 Hz) were also observed to be modulated by the phases of theta oscillations. These findings suggest the existence of phase-amplitude coupling in the neocortex during auditory working memory, and provide a highly resolved timeline to evaluate brain dynamics. In addition, the ERPAC results also support the involvement of theta-gamma and theta-beta neural coding mechanisms in cognitive and memory tasks. Collectively, these findings demonstrate the existence of ERPAC within the frontal and parietal regions during an auditory working memory task using complex chords as stimuli, and prompt the use of complex stimuli in studies that are closer to the real-life applications of cognitive evaluations, mental treatments, and brain-computer interfaces.

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Ting Huang

Papers

Event-Related Phase-Amplitude Coupling During Working Memory of Musical Chords