Modulation of aperiodic EEG activity provides sensitive index of cognitive state changes during working memory task

To better understand cognitive processes, it is essential to examine the interplay between periodic (oscillatory) and aperiodic electrophysiological brain activity. In this study, we aim to clarify how the periodic and aperiodic electrophysiological components respectively reflect the cognitive processes involved in working memory. Fiftyseven participants performed an n-back task while their brain activity was recorded using EEG. The analysis of both components of the EEG spectrum during task performance indicate that both periodic and aperiodic activities exhibit distinct taskrelated spatiotemporal dynamics that are closely related to cognitive demands. The results indicate that the substantial changes traditionally attributed to theta oscillations in working memory tasks are, in fact, due to shifts in the spectral slope of aperiodic activity. This suggests that the modulation of aperiodic activity associated with cognitive control processes may provide a more sensitive index of cognitive state changes than previously recognised. To validate our findings, we also used these analysis methods in another working memory task, which showed similar patterns of periodic and aperiodic activity. Our findings challenge the conventional understanding of theta oscillations in cognitive processing and question the routine practice of EEG baseline correction in time-frequency analysis, which may obscure significant modulations in continuous working memory tasks. Consequently, the inclusion of aperiodic activity as a fundamental component of EEG analysis is critical to the accurate representation of the neural basis of cognition.