COGPITStudy: COGnitive Function, Performance and Irregular Timing of Sleep –An epidemiology and mathematical modeling approach–

• Applicant: Dr. Dorothee Fischer
• Subject Area: Epidemiology and Medical Biometry/Statistics ; Public Health, Healthcare Research, Social and Occupational Medicine
• Term: from 2020 to 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 439835894

• Final Report Year: 2023

Final Report Abstract

Fatigue and impaired cognitive performance are serious concerns in safety-critical sectors that demand around-the-clock duties including shift work, night work, and time zone changes. Such schedules often result in insufficient and irregular sleep. Regular sleep timing is by now considered as important to health and performance as sufficient sleep duration. This project aimed to: Objective (1), determine potential adverse effects of irregular sleep on cognitive function using new metrics for quantifying sleep regularity in a prospective cohort of US Hispanics; and Objective (2), apply a mathematical model of sleep-wake regulation to improve shift work schedules so that sleep is more regular and predicted cognitive performance is improved in safety-critical occupations in aviation (i.e., pilots). In Objective (1), the association between low cognitive performance and sleep regularity (assessed from 3-7 days of actigraphy data using the Sleep Regularity Index, SRI) was examined in 1,006 middle-aged participants from the ‘Hispanic Community Health Study’, using logistic and multivariable regression models. Per standard deviation higher SRI scores, the odds of having low cognitive performance were ~20% lower. In summary, irregular sleep was among the strongest sleep-wake behavioral correlates of low cognitive performance in this middle-aged population. Given the potential of sleep-wake behavior for modification, targeting midlife irregular rhythms may decrease dementia risk. In Objective (2), a validated, bio-mathematical model of human sleep and cognitive performance, based on the adenosine system in the brain, was applied to performance data from 24 pilots in the helicopter emergency medical services (HEMS). The model captured the observed key dynamics at the group-average level but failed to accurately predict individual-level performance. To improve the model’s individual predictive power, data from two brain-imaging studies were used that collected both adenosine receptor availability and cognitive performance in the same individuals. Initial findings showed good model congruence with individuals that are highly susceptible to sleep-loss induced cognitive impairments, suggesting modeling individual changes in the adenosine system can improve model predictions of individual changes in cognitive performance. In an additional project, the sensitivity to light was examined as a potential physiological factor to promote irregular sleep-wake patterns. Using a mathematical modeling approach, circadian, sleep homeostatic, and light sensitivity parameters were investigated. Three out of five light sensitivity parameters meaningfully affected sleep regularity. The results suggest that irregular sleep can result from an interaction between environmental restrictions and individual physiological factors, including individual differences in the sensitivity to the timing and intensity of light exposure. In a second additional project, the day-to-day regularity of light exposure was assessed using a modified sleep-regularity metric (the Composite Phase Deviation metric, CPD) to examine the association between sleep regularity and light regularity. The findings suggest that occasional exposure to bright light, such as spending weekends outdoors, may help improve sleep, while regular exposure to indoor dim-light may allow other (physiological) factors, such as light sensitivity, to influence sleep-wake behavior, e.g., towards patterns that are considered detrimental to health.

Publications

• A model-based investigation of physiological factors that promote irregular sleep/wake patterns. Sleep Medicine, 100, S43.
  Fischer, D.; Klerman, E.B.; Cain, S.W. & Phillips, A.J.
  
• Light in ecological settings: Entrainment, circadian disruption, and interventions. Progress in Brain Research, 303-330. Elsevier.
  Fischer, D & Hilditch, CJ
  
• Shining light on sleep regularity – daytime light exposure and nighttime sleep patterns. Published conference abstract. J Sleep Res Vol31(Suppl 1);P640.
  Fischer D., Roenneberg T. & Vetter C.
  
• Jet Lag, Sleep Timing, and Sleep Inertia. The Handbook of Fatigue Management in Transportation, 195-213. CRC Press.
  Hilditch, Cassie J. & Fischer, Dorothee