Disruption of The Presumed Circadian Sleep Maintenance Zone Predicts Cognitive Impairment in Older Adults.

Background
Age-related changes in sleep quality are associated with cognitive impairment in older adults and may play a role in the trajectory of cognitive decline in Alzheimer’s disease. Circadian dysregulation of the sleep maintenance zone could in part explain these changes in sleep quality and might be associated with cognitive impairment observed in older adults.
Methods
Community dwelling older adults (N = 112; mean age = 71.6, SD = 7.4; 63% female) with Mini-Mental State Examination scores > 24/30 participated in the study. MCI status was determined using the Montreal Cognitive Assessment (MCI: MoCA < 26/30). Circadian regulation and sleep quality was assessed using the MotionWatch 8© actigraphy system (MW8; camntech). Following 14d actigraphy, cognitive function was assessed using the cognitive subscale of the Alzheimer’s disease assessment scale (ADAS-Cog). Partial correlations, controlling for age, sex, time of cognitive testing, and number of days of actigraphy, determined whether circadian regulation and sleep parameters were associated with cognitive performance. We operationally defined the sleep maintenance zone as the early morning hours prior to habitual wake-up (i.e., 3:00 to 5:59).
Results
Age was fairly strongly related to ADAS-Cog performance (r = .46, p < .001). Older age was also associated with greater nocturnality of activity (r = .19, p < .05); more specifically, older age was associated with a greater proportion of activity occurring between 3:00 and 5:59 (r = .21, p < .05) and with a lower proportion of activity occurring between 18:00 and 20:59 (r = -.24, p < .05). Poorer ADAS-Cog performance was associated with greater nocturnality of activity (r = .32, p < .001), with a greater proportion of activity occurring from 3:00 to 5:59 (r = .22, p < .05) and from 6:00 to 8:59 (r = .33, p < .001), and with a lower proportion of activity occurring from12:00 to 14:59 (r = -.19, p < .05), 18:00 to 20:59 (r = -.29, p < .01), and 21:00 to 23:59 (r = -.19, p < .05).
Conclusions
Our results support the hypothesis that circadian dysregulation of the sleep maintenance zone is associated with cognitive impairment.