Daytime rest: Association with 24‐h rest–activity cycles, circadian timing and cognition in older adults

Abstract

Growing epidemiological evidence points toward an association between fragmented 24‐h rest–activity cycles and cognition in the aged. Alterations in the circadian timing system might at least partially account for these observations. Here, we tested whether daytime rest (DTR) is associated with changes in concomitant 24‐h rest probability profiles, circadian timing and neurobehavioural outcomes in healthy older adults. Sixty‐three individuals (59–82 years) underwent field actigraphy monitoring, in‐lab dim light melatonin onset assessment and an extensive cognitive test battery. Actimetry recordings were used to measure DTR frequency, duration and timing and to extract 24‐h rest probability profiles. As expected, increasing DTR frequency was associated not only with higher rest probabilities during the day, but also with lower rest probabilities during the night, suggesting more fragmented night‐time rest. Higher DTR frequency was also associated with lower episodic memory performance. Moreover, later DTR timing went along with an advanced circadian phase as well as with an altered phase angle of entrainment between the rest–activity cycle and circadian phase. Our results suggest that different DTR characteristics, as reflective indices of wake fragmentation, are not only underlined by functional consequences on cognition, but also by circadian alteration in the aged.

Napping and circadian sleep–wake regulation during healthy aging

“…A critical feature of sleep and wakefulness that deteriorates with age is the ability to maintain these states over extended periods of time [28], such that older individuals may encounter difficulties staying asleep at night (sleep is fragmented) and maintaining waking alertness through the day (naps are more prevalent). In line, we recently observed that increased actimetry-derived daytime rest frequency is not only associated with an altered 24-hour rest-activity distribution, but also reduced episodic memory performance [29]. We also observed that individuals who rest later in the day go to bed later with respect to their circadian phase, thereby indicating circadian misalignment.…”

“…Data considered here were collected during three phases: (1) a telephone interview and screening visit, (2) a pre-laboratory field actimetry study, and (3) an in-laboratory study, encompassing a 56-hour stay. Melatonin and actimetry data from a sub-sample of individuals included here have been published previously [29].…”

“…Psychomotor vigilance performance was assessed after each nap opportunity (dots). was conducted under controlled conditions according to light input (<5 lux during scheduled wakefulness; 0 lux during scheduled sleep opportunities), isocaloric food intake (standardized meals every 4 hours), temperature (~ 19°C) and body posture (semi-recumbent position during scheduled wakefulness and recumbent during sleep opportunities; see also [29] for further specifications on light settings). Participants were not allowed to stand up, except for regularly scheduled bathroom visits and did not have any indications of time of day.…”

Circadian rapid eye movement sleep expression is associated with brain microstructural integrity in older adults

“…Eighty-six healthy retired older participants aged between 59–82 years were recruited. Inclusion criteria have been described elsewhere 49 . Briefly, participants were screened for psychoactive drug impacting the central nervous system, major sleep disorders (mean apnea/hypopnea index [events/hour] ± SD = 5.8 ± 4.8; mean periodic limb movement events/hour ± SD = 3.7 ± 8.2), recent psychiatric disorders (moderate/severe depression, Beck Depression Inventory score > 19; severe anxiety, Beck Anxiety score > 30), brain trauma, diabetes and body mass index ≤ 18 kg/m² and ≥ 30 kg/m², smoking, excessive alcohol ( > 14 units/week) or caffeine ( > 4 cups/day) and drug consumption, and cognitive status (Mini Mental State Examination score < 26, Mattis Dementia Rating Scale score < 130).…”

“…The duration of wakefulness in the last cycle was restricted to 40 min such that the recovery night started at habitual sleep time. During the entire in-lab protocol, controlled laboratory conditions were applied including lighting (4.5–5 lux during wakefulness and < 1 lux during scheduled sleep opportunities, see also 49 for further specifications about light settings), ambient temperature of approximately 19°C, semi-recumbent body posture during wake periods and recumbent during sleep opportunities, and isocaloric food intake (individually standardized meals every 4 h). Participants were not allowed to stand up, except for regularly scheduled bathroom visits, and they did not have any indications of time of day.…”