The looping lullaby: closed-loop neurostimulation decreases sleepers' sensitivity to environmental noise

Study ObjectiveSleep is critical for physical and mental health. However, sleep disruption due to noise is a growing problem, causing long-lasting distress and fragilizing entire populations mentally and physically. Here for the first time, we tested an innovative and non-invasive potential countermeasure for sleep disruptions due to noise. MethodsWe developed a new, modeling-based, closed-loop acoustic neurostimulation procedure (CLNS) to precisely phase-lock stimuli to slow oscillations (SO). We used CLNS to align, soft sound pulses to the start of the SO positive deflection to boost SO and sleep spindles during non-rapid eye movement (NREM) sleep. Participants underwent three overnight EEG recordings. The first night served to determine each participants individual noise arousal threshold. The remaining two nights occurred in counterbalanced order: in the "Disturbing night", loud, real-life noises were repeatedly presented; in the "Intervention night", similar loud noises were played while using the CLNS to boost SO. All experimental manipulations were performed in the first three hours of sleep; participants slept undisturbed for the rest of the night. ResultsIn contrast to the Disturbing night, the probability of arousals caused by noise was significantly decreased in the Intervention night. Moreover, the CLNS intervention increased NREM duration and sleep spindle power across the night. ConclusionsThese results show that our CLNS procedure can effectively protect sleep from disruptions caused by noise. Remarkably, even in the presence of loud environmental noise, CLNS soft and precisely timed sound pulses played a beneficial role in protecting sleep continuity. This represents the first successful attempt at using CLNS in a noisy environment. Statement of SignificanceExposure to noise during sleep impairs sleep quality, leading to impaired biological functioning, decreased day-time performance and higher occurrence of accidents. Slow wave sleep is hallmarked by slow oscillations (SO) and sleep spindles, both of which are markers of sleep stability. In previous experiments, acoustic stimulation has shown potential in enhancing SO and sleep spindles. Whether these manipulations also work to stabilize sleep against the disrupting effects of environmental noise remains unclear. Here we use a new closed-loop approach to precisely align subtle acoustic stimuli with SO phase. We show that this method effectively stabilizes sleep in the presence of noise. Our results bear crucial relevance for improving sleep in the general public and in many high-risk professions.