Changes in white matter functional networks during wakefulness and sleep

Area of Science:

• Neuroimaging
• Sleep Science
• White Matter Physiology

Background:

• Blood oxygenation level-dependent (BOLD) signals in white matter (WM) encode neural activity.
• Previous studies focused on gray matter functional connectivity during sleep.
• WM functional characteristics during sleep remained largely unknown.

Purpose of the Study:

• To investigate the functional characteristics of WM during different sleep stages.
• To map changes in WM functional networks and signal fluctuations across the sleep-wake cycle.

Main Methods:

• Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data were collected from 66 healthy participants during wakefulness and NREM sleep.
• Clustering analysis was used to construct 10 stable WM functional networks.
• Functional connectivity and regional signal fluctuation amplitude were evaluated across low-frequency bands.

Main Results:

• WM functional connectivity between superficial and middle layers decreased from wakefulness to sleep.
• Connectivity between deep and cerebellar networks varied across sleep stages (higher in light sleep, lower in wakefulness and deep sleep).
• Regional fluctuation amplitude was higher in light sleep and lower in deep sleep; slow-wave activity correlated with WM functional connectivity and fluctuation strength.

Conclusions:

• Neural activity in WM is modulated by the sleep-wake cycle.
• This study provides initial physiological evidence and mapping of functional changes in WM during sleep.