Dynamic functional MRI markers of drowsiness during sleep onset period.

The present use of ocular activity to enhance the temporal resolution of the classification of sleep onset period (SOP) allowed to reveal an increase in the power of oscillations in the BOLD signal at 0.05 Hz in the brain, particularly in sensory cortices, as soon as the first signs of drowsiness. These changes were evident in the "likely drowsy" state of SOP, representing early sleep-related vigilance fluctuations, often encountered even during activities like driving. Our findings show changes in the BOLD signal even before conventional indicators of sleep onset.