Phase precession of spindle-slow oscillation coupling across the human brain

Spindles and slow oscillations (SO) are fundamental elements of the NREM sleep microarchitecture, often co-occurring in a phase-dependent manner, and this cross-frequency coupling is critical for the temporal coordination of neural activity in sleep. However, spindles and SO occur at different times in different regions, and it is unclear how the coupling of these oscillations is organized across the brain. Here, we provide evidence in humans for a novel spatiotemporal organization of spindle-SO coupling, characterized by a precession of the SO phase of spindles along the brain's anterior-posterior axis. We show that this phase precession relationship is a robust phenomenon and can be quantified across individual subjects. Moreover, the integrity of phase precession strength and slope declines with advancing age. These findings provide new insight into the temporal coordination of sleep rhythms across brain space, linking this coordination to a canonical principle of neural coding.