EEG Microstates and Related Brain Networks During Light Sleep

Light sleep, including Stages N1 and N2, constitutes more than half of total human sleep duration. It serves essential functions in transitioning from wakefulness to deep sleep and in memory processing. Previous studies have identified four consistent electroencephalogram (EEG) microstates during wakefulness and sleep. Simultaneous EEG and functional magnetic resonance imaging (fMRI) studies have shown that EEG microstates are associated with specific brain functional networks during wakefulness and slow wave sleep. However, the relationship between microstates and brain networks during light sleep remains unexplored. To address this gap, simultaneous EEG-fMRI data acquired during light sleep were used to examine the correspondence between microstates and brain networks. The EEG microstate informed fMRI analysis revealed that Microstate C was associated with the cerebellum, and Microstate D was associated with the thalamus and motor areas during both N1 and N2 sleep. No significant results were found in Microstate A or B during N1. Additionally, linear mixed-effect analysis verified that Microstate D's association with the motor network and thalamus persisted during both N1 and N2, though their activity showed opposing trends between stages: Microstate D-related thalamic activity was lower in N1 than in N2, whereas the motor cortex exhibited the opposite pattern. These findings highlight distinct relationships between EEG microstates and brain networks during N1 and N2 sleep and implicate the thalamus and motor cortex as key neural substrates during light sleep.