Cluster-based permutations revealed a significant linear decrease of spontaneous oscillatory activity with increasing age for the slow frequency range of 0.5–6.5 Hz (p = .009). The decrease in slow wave power was widespread over large parts of the brain, affecting almost the entire sensor array (Figure 1a). This negative relation is illustrated in the scatterplot in Figure 1b: For each subject, we averaged power estimates from all frequency × sensor samples within the cluster and correlated these values with age. Pearson r was −.58 (p < .001). In Figure 2, participants were divided into a “younger” (18–54 years of age, n = 26) and “older” (55–89 years of age, n = 27) group, based on a median split. The graph shows reduced slow wave power for “older” compared to “younger” participants.
