Optimizing sounds for the driving of sleep oscillations by closed-loop auditory stimulation

Recent studies have shown that slow oscillations (SOs) can be driven by rhythmic auditory stimulation, which deepens slow wave sleep (SWS) and improves memory and the immune-supportive hormonal milieu related to this sleep stage. While different attempts have been made to optimize the driving of the SO by changing the number of click stimulations, no study has yet investigated the impact of applying more than five clicks in a row. Likewise, the importance of the type of sounds in eliciting brain responses is presently unclear. In a study of 12 healthy young participants (10F; aged 18-26), we applied an established closed-loop stimulation method, which delivered sequences of 10 pink noises, 10 pure sounds (B note of 247 Hz), 10 pronounced <a> vowels, 10 sham, 10 variable sounds and 10 oddball sounds on the up phase of the endogenous SO. By analysing area under the curve (auc), amplitude, and ERP, we explored whether the nature of the sound had a differential effect on driving SOs. We showed that every stimulus in a 10 click sequence, induces an SO response. Interestingly, all three types of sounds we tested triggered SOs. However, pink noise elicited a more pronounced response compared to the other sounds, which was explained by a broader topographical recruitment of brain areas. Our data further suggest that varying the sounds may partially counteract habituation.