Homeostatic response to sleep deprivation and circadian rhythmicity are intact in older adults with insomnia

Study Objectives We examined whether homeostatic sleep drive and circadian rhythmicity differ in older adults with insomnia (OAI) compared to older good sleepers (GS). Methods OAI (n = 37) and GS (n = 30) participated in a 60-h in-lab study with sleep deprivation and constant routine paradigms. Homeostatic sleep drive was assessed by examining the effect of sleep deprivation on delta EEG power and theta EEG power, and repeated sleep latency tests. Circadian rhythm was assessed with salivary melatonin (phase and amplitude), core body temperature (phase, amplitude, and mesor), and sleep latency during a constant routine paradigm. Mixed models were used to assess interactions of group (OAS vs GS) with homeostatic sleep and circadian effects. Results Compared to GS, OAI showed a greater linear increase in waking theta power during sleep deprivation, but the two groups did not show differential responses to sleep deprivation in delta EEG, or in repeated sleep latency tests. The two groups did not differ in circadian phase or amplitude of melatonin or core body temperature rhythms. OAI had a significantly elevated core body temperature mesor compared to GS. Conclusions Homeostatic response to sleep deprivation was intact in OAI compared to GS; theta EEG power suggested a greater homeostatic response in OAI. Circadian rhythm amplitude and phase were similar in OAI compared to GS. Elevated body temperature mesor in OAI may indicate elevated physiological arousal. These findings suggest that effective treatments for insomnia in older adults may leverage intact sleep and circadian regulatory mechanisms, rather than repair defective sleep and circadian regulation.