Abstract
Physical activity is beneficial for health. It has been shown to improve brain functioning and cognition, reduce severity of mood disorders, as well as facilitate healthy sleep and healthy aging. Sleep has been studied in healthy aged mice and absolute slow-wave-activity levels (SWA, electroencephalogram power between 0.75 and 4.0 Hz) in non-rapid-eye-movement sleep (NREM) were elevated, suggesting changes in brain connectivity. To investigate whether physical activity can diminish this aging-induced effect, mice of three age groups were provided with a running wheel (RW) for 1–3 months (6-months-old, n = 9; 18-months-old, n = 9; 24–months-old, n = 8) and were compared with control sedentary mice (n = 11, n = 8 and n = 9 respectively). Two weeks before the sleep-wake recordings the running wheels were removed. The electroencephalogram (EEG) and electromyogram were continuously recorded during undisturbed 24 h baseline (BL) and a sleep-deprivation was conducted during the first 6 h of the second day. Increased waking and decreased NREM sleep was found in the young RW mice, compared to young controls. These effects were not evident in the 18 and 24 months old mice. Unlike sleep architecture, we found that SWA was altered throughout the whole age spectrum. Notably, SWA was increased with aging and attenuated with exercise, exhibiting the lowest levels in the young RW mice. To utilize the cross-age revealing features of SWA, we applied machine learning techniques and found that characteristic information regarding age and exercise was enclosed in SWA. In addition, with cluster analysis, we could classify and accurately distinguish the different groups based solely on their SWA. Therefore, our study comprises a three-fold contribution: (a) effects of exercise on sleep are sustained following 2 weeks after removal of the wheel, (b) we show that EEG SWA can be used as a physiological marker of brain age in the mouse, (c) long-term voluntary regular age-matched exercise leads to a younger phenotype.
Highlights
Sleep is a vital physiological routine that has a critical function in promoting the health of all living organisms
Three control groups in which mice were sedentary throughout their life (n = 11, 8, and 9 with increasing age respectively) and three running-wheel (RW) groups where a running wheel was introduced in the cage (n = 9, 9 and 8 with increasing age respectively), for voluntary use in a daily basis in order for the mice to be exposed to a type of aerobic exercise as preferred in human studies
In the 18 months old mice that had the running wheel, the Analysis of variance (ANOVA) showed a stronger increase in NREM sleep and decrease in waking, compared to age-matched controls, these effects did not survive post hoc multiple comparisons correction (Table 1)
Summary
Sleep is a vital physiological routine that has a critical function in promoting the health of all living organisms. It is regulated by two processes, the circadian and homeostatic process (Borbély et al, 2016; Achermann and Borbely, 2017). Several sleep parameters deteriorate and the overall sleep quality is impaired (Landolt et al, 1996; Carrier et al, 2001; Crowley, 2011). In addition to the increased SWA levels, the overall morphology of the slow-waves was shown to be changed, suggesting cortical brain alterations (Panagiotou et al, 2017)
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