Periodic and aperiodic contributions to theta‐beta ratios across adulthood

The ratio of fronto‐central theta (4–7 Hz) to beta oscillations (13–30 Hz), known as the theta‐beta ratio, is negatively correlated with attentional control, reinforcement learning, executive function, and age. Although theta‐beta ratios have been found to decrease with age in adolescents and young adults, theta has been found to increase with age in older adults. Moreover, age‐related decrease in individual alpha peak frequency and flattening of the 1/f aperiodic component may artifactually inflate the association between theta‐beta ratio and age. These factors lead to an incomplete understanding of how theta‐beta ratio varies across the lifespan and the extent to which variation is due to a conflation of aperiodic and periodic activity. We conducted a partially preregistered analysis examining the cross‐sectional associations between age and resting canonical fronto‐central theta‐beta ratio, individual alpha peak frequency, and aperiodic component (n = 268; age 36–84, M = 55.8, SD = 11.0). Age was negatively associated with theta‐beta ratios, individual peak alpha frequencies, and the aperiodic exponent. The correlation between theta‐beta ratios and age remained after controlling for individual peak alpha frequencies, but was nonsignificant when controlling for the aperiodic exponent. Aperiodic exponent fully mediated the relationship between theta‐beta ratio and age, although beta remained significantly associated with age after controlling for theta, individual peak alpha, and aperiodic exponent. Results replicate previous observations and show age‐related decreases in theta‐beta ratios are not due to age‐related decrease in individual peak alpha frequencies but primarily explained by flattening of the aperiodic component with age. The fronto‐central theta‐beta ratio is negatively correlated with age, but it is unclear if this is due to age‐related shifts in individual peak alpha frequencies, flattening of the aperiodic 1/f component, or a unique aging process. In a large adult sample (n = 268; age 36–84), the aperiodic exponent fully mediated the negative relationship between age and theta‐beta ratio, suggesting theta‐beta ratio and aperiodic exponent are highly confounded measures across the lifespan.