Abstract
Objective. Recent evidence reports cognitive, metabolic, and sleep restoration benefits resulting from the enhancement of sleep slow-waves using auditory stimulation. Our objective is to make this concept practical for consumer use by developing and validating an electroencephalogram (EEG) closed-loop system to deliver auditory stimulation during sleep to enhance slow-waves. Approach. The system automatically detects slow-wave sleep with 74% sensitivity and 97% specificity and optimally delivers stimulation in the form of 50 ms-long tones separated by a constant one-second inter-tone interval at a volume that is dynamically modulated such that louder tones are delivered when sleep is deeper. The system was tested in a study involving 28 participants (18F, 10M; 36.9 ± 7.3 years old; median age: 40 years old) who used the system for ten nights (five nights in a sham condition and five in a stimulation condition). Four nights in each condition were recorded at-home and the fifth one in-lab. Main results. The analysis in two age groups defined by the median age of participants in the study shows significant slow wave activity enhancement (+16.1%, p < 0.01) for the younger group and absence of effect on the older group. However, the older group received only a fraction (57%) of the stimulation compared to the younger group. Changes in sleep architecture and EEG properties due to aging have influenced the amount of stimulation. The analysis of the stimulation timing suggests an entrainment-like phenomenon where slow-waves align to the stimulation periodicity. In addition, enhancement of spindle power in the stimulation condition was found. Significance. We show evidence of the viability of delivering auditory stimulation during sleep, at home, to enhance slow wave activity. The system ensures the stimulation delivery to be at the right time during sleep without causing disturbance.
Highlights
In this study we examine the effect of stimulation on slow-wave activity (SWA) throughout non-rapid eye movement sleep (NREM) sleep and in particular the considered NREM epochs while total SWA (CSWA) increase which according to equation (2), should result in a more efficient dissipation of sleep-need
The normalized confusion matrix associated with the real-time automatic sleep staging algorithm is shown in table 1 for all participants and for two participant subsets: (a) younger than 40 years old, and (b) 40 years old or older
We have developed an integrated closed-loop sleep-wearable system that monitors the sleep EEG, detects the periods when auditory stimulation can be applied to enhance SWA, and automatically modulates the properties of the stimulation to optimize the effect without causing any sleep disturbance
Summary
Closed-loop system to deliver auditory stimulation during slow wave sleep. A sleep wearable system was developed for this study which monitors sleep by processing the EEG signal acquired from a frontal location in real-time (Fpz; as per the 10–20 standard [32]). The reference electrode is on the right mastoid (M2). The system records two (right and left) electrooculogram signals (EOG) which, together with the EEG, are used for manual sleep staging. The right EOG electrode is positioned above the right eyebrow and the left EOG electrode is positioned on the left outer canthus. An adjustable headband holds the Fpz electrode, the EOG electrodes and the speakers. Processing of the signals is performed in an integrated unit with an embedded micro-processor connected to the headband (see figure 2)
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