The Association between Working Memory Precision and the Nonlinear Dynamics of Frontal and Parieto-occipital EEG Activity.

AbstractWorking memory (WM) research in electrophysiology reveals that brain areas communicate through macroscopic oscillatory activities across multiple frequency bands. Interactions across different frequency components generate nonlinear amplitude modulation (AM) in the observed signal. Traditionally, AM is expressed as the coupling strength between the signal and a prespecified modulator at a lower frequency. Therefore, the idea of AM and coupling cannot be studied separately. In this study, 33 participants completed a color recall task while their brain activity was recorded through EEG. The AM of the EEG data was extracted using the Holo-Hilbert spectral analysis (HHSA), an adaptive method based on the Hilbert-Huang transforms. The results showed that frontal theta power enhancement and parieto-occipital alpha/beta power suppression predicted individual differences in WM precision. Furthermore, the AM of parieto-occipital alpha/beta power predicted WM precision after presenting a target-defining probe array. The phase-amplitude coupling (PAC) between the frontal theta phase and parieto-occipital alpha/beta AM increased with WM load while processing incoming stimuli, but the PAC itself did not predict the subsequent recall performance. These results suggest frontal and parieto-occipital regions communicate through theta-alpha/beta PAC. However, the overall recall precision depends on the alpha/beta AM following the onset of the retro cue.