The timing of sleep spindles is modulated by the respiratory cycle in humans

Abstract

Coupling of sleep spindles with cortical slow waves and hippocampus sharp-waves ripples is crucial for sleep-related memory consolidation. Recent literature evidenced that nasal respiration modulates neural activity in large-scale brain networks. In the rodent, this respiratory drive strongly varies according to vigilance states. Particularly, during sleep, respiration promotes the coupling between hippocampal sharp-wave ripples and cortical DOWN/UP state transitions. However, no study has examined whether sleep spindles could be respiration-modulated in humans. In this work, we aimed to investigate the influence of breathing on brain oscillations during non-rapid-eye-movement stage 2 sleep (N2) in humans by examining the coupling between sleep spindles and respiration cycle. Full night polysomnography of twenty healthy participants were analysed. Spindles and slow waves were detected during N2 sleep stage. Spindle-related sigma power as well as spindle and slow waves events were analysed according to the respiratory phase. We found a significant coupling between slow and fast spindles with respiration cycle, with enhanced sigma activity and probability of occurrence of spindles during the middle part of the expiration phase. A different coupling was observed between breathing and slow waves that were more distributed around both respiration phase transitions. Our findings suggest that breathing cycle influences the dynamics of brain activity during non-rapid-eye-movement sleep. This may enable sleep spindles to synchronize with other brain rhythms including hippocampus sharp wave ripples and facilitate information transfer between distributed brain networks.