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

• Sigma activity is enhanced during the expiratory phase of respiration in non-rapid-eye-movement sleep. • Both slow and fast spindle events occurrence significantly increases during the middle part of the expiration phase. • Breathing exerts a lower biphasic effect on slow waves occurrence, which increases during respiration phase transitions. 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 rodents, this respiratory drive strongly varies according to vigilance states. Whether sleep oscillations are also respiration-modulated in humans remains open. In this work, we investigated the influence of breathing on sleep spindles during non-rapid-eye-movement sleep in humans. Full night polysomnography of twenty healthy participants were analysed. Spindles and slow waves were automatically detected during N2 and N3 stages. Spindle-related sigma power as well as spindle and slow wave events were analysed according to the respiratory phase. We found a significant coupling between both slow and fast spindles and the respiration cycle, with enhanced sigma activity and occurrence probability of spindles during the middle part of the expiration phase. A different coupling was observed for slow waves negative peaks which were rather distributed around the two respiration phase transitions. Our findings suggest that breathing cycle influences the dynamics of brain activity during non-rapid-eye-movement sleep. This coupling may enable sleep spindles to synchronize with other sleep oscillations and facilitate information transfer between distributed brain networks. [ABSTRACT FROM AUTHOR]