Human Brain-Wide Activation of Sleep Rhythms

During sleep, our brain undergoes highly synchronized activity, orchestrated by distinct neural rhythms. Little is known about the associated brain activation during these sleep rhythms, and even less about their functional implications. In this study, we investigated the brain-wide activation underlying human sleep rhythms by employing simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) in 107 participants during overnight sleep. We identified a significant coupling between slow oscillations (SO) and spindle events during non-rapid eye movement (NREM) sleep, particularly at the UP-state of SOs. This coupling was associated with increased activation in the thalamus and hippocampus, showing a brain-wide activation that resembles episodic memory processing, yet is distinctly dissociated from task-related activation. Moreover, this SO-spindle coupling was linked to a selective increase in functional connectivity from the hippocampus to the thalamus, and from the thalamus to the neocortex, particularly the medial prefrontal cortex. These findings suggest that the thalamus plays a crucial role in coordinating the hippocampal-cortical dialogue during sleep.