Modeling napping, post-lunch dip, and other variations in human sleep propensity

Area of Science:

• Chronobiology
• Sleep Science
• Mathematical Modeling

Background:

• Sleep propensity (SP) exhibits significant 24-hour variations, including a post-noon dip and an early evening trough.
• Existing models often treat SP as discrete or do not fully capture its continuous nature across the day.

Purpose of the Study:

• To develop a continuous 24-hour model of sleep propensity (SP).
• To specifically model the post-noon nap zone and the early evening SP trough.
• To investigate the interaction between homeostatic and circadian sleep drives.

Main Methods:

• A modified 2-process model was employed, replacing the circadian threshold process with REM sleep propensity (R).
• Sleep propensity (SP) was modeled as a multiplicative interaction between homeostatic sleep drive (S) and circadian drive (R): SP = S x R.
• Model parameters were estimated using experimental data.

Main Results:

• The model predicts a 24-hour SP profile with a major nighttime peak, a secondary post-noon peak, and two local minima in the morning and early evening.
• Simulations showed that the post-noon nap zone's magnitude is influenced by the timing of nighttime sleep.
• The early evening SP trough remained stable across simulated sleep timing variations.

Conclusions:

• Sleep propensity can be effectively modeled as a continuous variable through the multiplicative interaction of homeostatic (S) and circadian (R) drives.
• The developed model aligns with observed variations in 24-hour sleep propensity patterns.