Thalamic dynamics orchestrate the recovery of tonic alertness during nocturnal sleep inertia

At dawn, we experience a shift from slumber to sentience following neurophysiological transitions, termed as sleep inertia (SI). Although resting-state fMRI studies have discovered brain reorganizations during SI, the neural basis underlying impaired alertness in SI remains unclear. We conduct simultaneous EEG-fMRI recordings on 26 adults with repeated measures of pre-sleep, nocturnal sleep and consecutive post-sleep awakenings. Using the psychomotor vigilance task (PVT) to probe tonic alertness, we discover that cingulo-opercular network (CON) activation, inclusive of thalamus, troughs upon awakening, and increments along with the post-sleep awake duration. The dynamic recovery of thalamus activity during SI depends on prior sleep architecture and the awake duration, mediating the PVT performances on awakening. Although CON connectivity remains stable, the connectivity changes between thalamus and frontoparietal network (FPN) are associated with changes of thalamic activation and PVT performances during SI. Collectively, thalamic activity and its coupling with the FPN support the restoration of tonic alertness during SI, providing a concise framework for the neural mechanisms underlying cognitive recovery upon awakening.