Memory-relevant nap sleep physiology in healthy and pathological aging
Julia Ladenbauer, Josef Ladenbauer, Nadine Külzow, Agnes Flöel
Study objectives: Aging is associated with detrimental changes in sleep physiology, a process accelerated in Alzheimer’s disease (AD). Fine-tuned temporal interactions of NREM slow oscillations (SO) and spindles were shown to be particularly important for memory consolidation, and to deteriorate in healthy older adults. Whether this oscillatory interaction further declines in early stages of AD such as mild cognitive impairment (MCI) has not been investigated to date, but may have important therapeutic implications.
Methods: Here, we assessed differences in sleep architecture and memory-relevant SO, sleep spindles and their functional coupling during a 90-min nap between healthy young and older adults, and in older patients with MCI. Furthermore, associations of nap-sleep characteristics with sleep-dependent memory performance change were evaluated.
Results: We found significant differences between young and older healthy adults, and between young adults and patients with MCI, but not between healthy older adults and patients for several sleep metrics, including SO-spindle coupling. Moreover, sleep-dependent retention of verbal memories was significantly higher in young healthy adults versus older adults with and without MCI, but no difference between the two older groups was observed. Associations with sleep metrics were only found for pre-nap memory performances.
Conclusions: In conclusion, our results indicate changes in nap sleep physiology and sleep-related memory consolidation in older adults with and without MCI. Thus, interventions targeted at improving sleep physiology may help to reduce memory decline in both groups, but our study does not indicate additional benefits for patients with MCI.