Brain oscillations and sleep microarchitecture: From EEG to fMRI.

This chapter covers the role of brain oscillations in shaping the microarchitecture of sleep and their role in physiological and pathological states. Neural oscillations (delta to gamma frequencies) are fundamental to the structure of sleep stages and play a central role in cognitive and restorative processes of the human brain. This chapter discusses how different oscillatory signatures characterize non-rapid eye movement (NREM) and rapid eye movement (REM) sleep, with slow waves dominating deep sleep and desynchronization in REM sleep. Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) are complementary to investigate sleep dynamics. EEG offers high temporal resolution in terms of oscillatory activity, and fMRI provides a spatial mapping of the network. The convergence of these modalities has provided new insights into sleep spindles, slow oscillations, and their association with large functional connections. Also emphasized in the chapter are the quantitative EEG metrics and advances in signal processing and machine learning that can help identify sleep stages and pathological patterns. The disruption of oscillatory dynamics in sleep disorders and neurodegenerative conditions is also explored as oscillatory biomarkers can be used as diagnostic and prognostic tools. Overall, the chapter highlights the implications of oscillatory dynamics as a common framework to connect sleep physiology with cognitive function and clinical applications, highlighting the potential for multimodal neuroimaging.