Changes in Brain Oscillatory Dynamics in Elderly Adults as a Consequence of Natural Aging

The oscillatory nature of slow waves during non-rapid eye movement (NREM) sleep has recently been proposed as crucial for the glymphatic system, facilitating the clearance of metabolic waste from the brain. While aging-related reductions in slow wave quantity and amplitude are well-documented and linked to this cleansing function, we propose that the rhythmic dynamics in which slow waves occur may also play a critical role. Thus, we introduce a novel classification of slow waves based on their dynamics into isolated waves and oscillation trains. Using overnight EEG recordings from young and elderly adults, we compared the proportions of each wave type. Additionally, we analyzed train composition, including the proportion of slow waves that initiate a train (lead waves) and the lengths of the trains. Elderly adults exhibited a higher prevalence of isolated waves and a lower proportion of oscillation trains. Moreover, while elderly adults showed a higher proportion of lead waves, their oscillation trains were shorter. We propose that natural aging may result in a less oscillatory brain state, potentially impairing cerebrospinal fluid pulsation and reducing the brain’s efficiency in cleansing pathogenic substances during sleep.