Aperiodic and oscillatory systems underpinning human domain-general cognition

Domain-general cognitive systems are essential for adaptive human behaviour, supporting various cognitive tasks through flexible neural mechanisms. From decades of fMRI studies, we know that a particular network of frontoparietal brain regions plays a role in supporting many different kinds of cognitive activity, with increased activity and information coding in response to increasing task demands. However, the electrophysiological mechanisms underlying this domain-general response to demand remain unclear. Here we used irregular-resampling auto-spectral analysis (IRASA) to separate the aperiodic and oscillatory components of concurrent MEG/EEG signals and analysed them with multivariate pattern analysis (MVPA) to investigate their roles in domain-general cognition. We found that both aperiodic (broadband power, slope, and intercept) and oscillatory (theta, alpha, and beta power) components coded both task demand and content across three cognitive tasks. Aperiodic broadband power in particular strongly coded task demand, in a manner that generalised across all subtasks, suggesting that modulation of aperiodic broadband power may reflect a domain-general response to multiple sorts of cognitive demand. Source estimation suggested that increasing cognitive demand decreased aperiodic activity across most of the brain, with the strongest modulations partially overlapping with the frontoparietal multiple-demand network. In contrast, oscillatory activity in the theta, alpha and beta bands showed more localised patterns of modulation, primarily in frontal (beta, theta) or occipital (alpha, theta) regions. The spatial pattern of demand-related modulation was significantly correlated across space in individuals, with positive correlations between theta and beta power, while both were negatively correlated with alpha power. These results provide novel insights into the electrophysiological underpinnings of human domain-general cognition, suggesting roles for both aperiodic and oscillatory systems, with changes in aperiodic broadband power being the clearest domain-general electrophysiological correlate of demanding cognitive activity.