During “resting state,” defined here as when one is not engaged in a cognitive task, the brain still emits spontaneous, rhythmic activity. Resting EEG measures a complex signal of voltage oscillations comprising a wide range of spectral frequencies (i.e., number of waves per second, Hz), that are subdivided into bands: delta (1–3.5 Hz), theta (3.5–7.5 Hz), alpha (7.5–12.5), beta (12.5–28) and gamma (above 28 Hz). The resting EEG is stable and highly heritable across all frequency bands. 69 These EEG rhythms are indicators of global brain states from the alert‐awake state to drowsiness and stages of sleep. In healthy adults, alpha and beta frequencies predominate the awake resting EEG, with alpha rhythm dominating during relaxation parietal‐occipitally and beta seen throughout the scalp with mental activation. 70 In COGA, resting‐state EEG is recorded while participants have their eyes closed (4.25 min) and again while they have their eyes open (4.25 min). Measures of resting EEG analyzed in COGA are (1) EEG power (absolute and relative) in each frequency band, representing the amount of neural activity in these frequency bands, 71 and
