Nightmare disorder shows reduced slow oscillation-dominant spindle coupling in NREM sleep
npj Biological Timing and Sleep June 22, 2026 I. Papp, Zoran Cvetković, Nazanin Biabani et al.
Nightmare disorder involves not only REM sleep but also altered NREM sleep physiology. In a retrospective case-control study of 26 adults with nightmare disorder and 32 controls, those with nightmare disorder showed reduced frontal slow-oscillation–spindle coupling, while delta–spindle coupling remained normal, resulting in lower coupling dominance. Stage-adjusted K-complex density across the first 6 hours of sleep was also lower in the nightmare disorder group. These findings suggest that nightmare disorder involves changes in NREM sleep microarchitecture, not just REM sleep, and warrant prospective confirmation.