Chylek, D., Fedor, S., Zhang, B., Nathan, V., Freedman, M., Stickgold, R., & Picard, R. (2025, June). Evidence for a deep sleep homeostatic response in ambulatory settings. SLEEP 2025: 38th Annual Meeting of the Associated Professional Sleep Societies, Seattle, WA, United States.

Abstract

Introduction: Sleep homeostasis (SH) regulates human sleep. Traditionally, EEG
slow-wave activity during deep sleep serves as a proxy for SH. We examine deep
sleep duration within the first two hours of sleep onset as a possible indicator of
SH pressure, using smartwatch data from daily life monitoring.

Methods: Sleep data were collected from 28 participants (ages 18-54, 57% female, 25% male,
18% unreported) monitored for 14 days of ambulatory use. We obtained nightly total sleep time
(TST) from Galaxy Watch 6 (GW), ActLumus measurements, daily morning surveys, and
combined the observed GW and Survey data as a fourth modality. The mean TST per night was
calculated from the four aforementioned variables. We also obtained nightly deep sleep data
from GW. Short nights were those with at least 30 minutes less sleep than participants’ median
TST. The mean difference in deep sleep during the first two hours of sleep following a short
night was calculated relative to (i) deep sleep in the first two hours of the short night and (ii)
participant’s median deep sleep duration in the first two hours of all sleep sessions. Results are
based on 50 short nights among participants with valid deep sleep data (mean TST across
participant’s night, alongside short night and following-night deep sleep durations, both
measured for the first two hours of sleep onset).

Results: The mean increase in deep sleep during the first two hours of the night following a
short night, compared to the previous night, was 6.3 minutes (p < 0.05) and compared to the participants’ median deep sleep time during the first two hours was 4.5 minutes (p < 0.05). Both were dose-dependent.

Conclusion: The night after a short-sleep-night showed a statistically significant increase in deep
sleep in the first two hours of sleep onset. This suggests that a smartwatch might help measure
sleep debt and provide a convenient way to collect data at home about daily sleep behaviors and
homeostatic regulation. Data was provided for analysis in February 2025.