Task-related changes in aperiodic activity are related to visual working memory capacity independent of event-related potentials and alpha oscillations

Individual differences in visual working memory capacity are related to slow-wave event-related potentials (ERPs) and suppression of alpha-band oscillatory power measured during the delay period of memory tasks using electroencephalography (EEG). However, recent evidence suggests that changes in the non-oscillatory, aperiodic features of the EEG signal may also contribute to working memory performance. We assessed several features of task-related changes in aperiodic activity including the spatial distribution, the effect of memory load, and the relationship between memory capacity, slow-wave ERPs, and alpha suppression. Eighty-four healthy individuals performed a continuous recall working memory task consisting of 2, 4 or 6 coloured squares while EEG was recorded. Aperiodic activity during a baseline and delay period was quantified by fitting a model to the background of the EEG power spectra using the FOOOF toolbox, which returned parameters describing the slope (exponent) and broadband offset of the spectra. The aperiodic exponent decreased (i.e., slope flattened) over lateral parieto-occipital electrodes but increased (i.e., slope steepened) over fronto-central electrodes during the delay period, whereas the offset decreased over parieto-occipital electrodes. These task-related changes in aperiodic activity were not altered by memory load. Larger increases in the aperiodic exponent were associated with higher working memory capacity measured from both the EEG task and a separate battery of complex span tasks, and this relationship was independent of slow-wave ERPs and alpha suppression. Our findings suggest that task-related changes in aperiodic activity during working memory are region specific and reflect an independent neural mechanism important for general working memory ability. ### Competing Interest Statement The authors have declared no competing interest.