"By age 74, slow wave sleep is often completely absent." #readingToday

By age 74, slow wave sleep is often completely absent. It is unclear whether this loss is due to a reduced need for that particular type of sleep, perhaps because of reduced physical activity and learning during the day or results instead from a loss of the ability to sustain such large-scale coordinated brain activity. If the latter explanation is true, we have to consider the possibility that reduced slow wave sleep may actually compound age-related problems—through both the resulting fatigue and also the poor memory that can stem from a lack of consolidation. It is even possible that relative reduction in the amount of slow wave sleep older people get compared to younger people eventually leads to some types of neural damage and might be linked to the gradual neurodegeneration that occurs with age. A recent study showed that the extent of medial prefrontal cortex atrophy in older adults predicted not only reductions in the slow waves they obtained but also a reduction in the amount of consolidation that occurred during that sleep.1 These are open topics of current research, however, so we will have to wait some time before the true causes and effects of sleep reduction in aging are known.

(Moon+ Reader Pro v2.3.4, The Secret World of Sleep: The Surprising Science of the Mind at Rest (MacSci))