Sleep Duration Phenotypes and Dynamic Homeostasis: A Wave-Model Framework

Are sleep duration and sleep intensity manifestations of the same phenotype, or are they distinct, complementary traits? We addressed this question by removing two major constraints on phenotype expression: limited sleep opportunity and prior sleep deficit. Across 105 baseline 8-h nights and 420 extended 14-h nights in 15 individuals, sleep duration and NREM intensity behaved as two largely independent traits. Baseline expression of each parameter predicted its own subsequent expression during chronic sleep abundance but failed to predict the companion trait either within or between conditions. We then evaluated external evidence from chronic 4- and 6-h sleep restriction alongside extreme natural sleep-duration phenotypes, interpreting these findings through the wave model of sleep dynamics. In this framework, sleep duration reflects the geometry of sleep-cycle oscillations, determined primarily by the width of the sleep-state stability landscape (formally represented as a Morse potential well). Conversely, NREM intensity reflects oscillation amplitude, providing a visible signature of deviation from homeostatic equilibrium. While acute perturbation alters amplitude, chronic perturbation induces adaptive changes in landscape width, preserving a characteristic deviation from equilibrium despite severe shifts in underlying state instability and allostatic strain.