Inter-individual differences in the dynamics of sleep homeostasis

Area of Science:

• Sleep science
• Neuroscience
• Chronobiology

Background:

• Sleep is regulated by circadian (Process C) and homeostatic (Process S) mechanisms.
• EEG slow-wave activity (SWA) quantifies NREM sleep intensity and reflects sleep homeostasis.
• Previous models primarily used average data, limiting understanding of individual differences.

Purpose of the Study:

• To quantify inter-individual differences in the parameters of the two-process sleep model.
• To establish a robust method for estimating homeostatic sleep (Process S) parameters on an individual basis.

Main Methods:

• Analysis of polysomnographic recordings from eight healthy males undergoing 40-hour sustained wakefulness.
• Modeling Process S using a saturating exponential function during wakefulness and exponential decline during sleep.
• Simultaneous parameter estimation by minimizing error between empirical SWA data and simulated Process S, with time constants constrained to physiological ranges.

Main Results:

• The developed method provided a satisfactory fit for both average and most individual data.
• Constraining time constants to physiological ranges improved model fit for all participants.
• Estimated time constants for Process S buildup ranged from 14.1 to 26.4 hours, and for decline from 1.2 to 2.9 hours.
• Significant inter-individual variability was observed in both the buildup and decline of Process S.

Conclusions:

• A robust methodology for individual-level parameter estimation of Process S was successfully established.
• This approach allows for a more precise understanding of individual sleep homeostasis.
• The findings highlight significant variability in sleep homeostatic regulation among healthy young males.