Phenotypic Interindividual Differences in the Dynamic Structure of Sleep in Healthy Young Adults

Abstract

Introduction

Evaluating the dynamic structure of sleep may yield new insights into the mechanisms underlying human sleep physiology.

Methods

We analyzed data from a 12-day, 11-night, strictly controlled laboratory study with an adaptation night, 3 iterations of a baseline night followed by a recovery night after 36 h of total sleep deprivation, and a final recovery night. All sleep opportunities were 12 h in duration (22:00–10:00) and recorded with polysomnography (PSG). The PSG records were scored for the sleep stages: rapid eye movement (REM) sleep; non-REM (NREM) stage 1 sleep (S1), stage 2 sleep (S2), and slow wave sleep (SWS); and wake (W). Phenotypic interindividual differences were assessed using indices of dynamic sleep structure – specifically sleep stage transitions and sleep cycle characteristics – and intraclass correlation coefficients across nights.

Results

NREM/REM sleep cycles and sleep stage transitions exhibited substantial and stable interindividual differences that were robust across baseline and recovery nights, suggesting that mechanisms underlying the dynamic structure of sleep are phenotypic. In addition, the dynamics of sleep stage transitions were found to be associated with sleep cycle characteristics, with a significant relationship between the length of sleep cycles and the degree to which S2-to-W/S1 and S2-to-SWS transitions were in equilibrium.

Discussion

Our findings are consistent with a model for the underlying mechanisms that involves three subsystems – characterized by S2-to-W/S1, S2-to-SWS, and S2-to-REM transitions – with S2 playing a hub-like role. Furthermore, the balance between the two subsystems within NREM sleep (S2-to-W/S1 and S2-to-SWS) may serve as a basis for the dynamic regulation of sleep structure and may represent a novel target for interventions aiming to improve sleep.

Keywords:

• polysomnography
• sleep stage transitions
• NREM/REM sleep cycles
• ultradian rhythm
• sleep phenotype

Data Sharing Statement

The data that support the findings of this study are available from the authors upon reasonable request.

Disclosure

Professor Hans PA Van Dongen reports personal fees from Jazz Pharmaceuticals, personal fees from Eisai Inc., grants from Federal Express Corporation, and grants from Trackthatsleep, outside the submitted work. The authors report no other conflicts of interest in this work.

Additional information

Funding

This work was partly supported by JSPS KAKENHI grants 15K16416 and 18K17891 and JST PRESTO grant JPMJPR19J3 to A.K., and by NIH grant R01HL70154 and ARO MURI grant W911NF2210223 to H.P.A.V.D.