Closed-loop vibration stimulation based on heart rhythm for reducing sleep inertia

The aim of this study was to determine whether closed-loop vibration stimulation, delivered at +3% of the heart rate frequency at an imperceptible intensity before waking, could reduce sleep inertia. Participants napped on a bed equipped with a woofer that delivered vibration stimulation every 5 min, starting 30 min before their scheduled wake time. The effects of the stimulation were assessed using a Psychomotor Vigilance Task performed immediately upon waking, along with the analysis of salivary cortisol and melatonin levels, as well as subjective arousal ratings based on the Karolinska Sleepiness Scale and the Stanford Sleepiness Scale. The results indicated that vibration stimulation at +3% of the heart rate frequency improved Psychomotor Vigilance Task reaction times and increased self-reported arousal scores, thus reducing sleep inertia compared with the control condition without stimulation. Additionally, salivary melatonin levels were lower immediately after waking. These findings suggest that closed-loop vibration stimulation at +3% of the heart rate frequency before waking could be an effective method to reduce sleep inertia. This non-invasive approach may facilitate cognitive recovery following sleep. Further research is required to investigate the underlying mechanisms, and confirm these findings across different populations and settings.