Effects of auditory sleep modulation approaches on brain oscillatory and cardiovascular dynamics

Abstract

Slow waves, the hallmark feature of deep nonrapid eye movement sleep, do potentially drive restorative effects of sleep on brain and body functions. Sleep modulation techniques to elucidate the functional role of slow waves thus have gained large interest. Auditory slow wave stimulation is a promising tool; however, directly comparing auditory stimulation approaches within a night and analyzing induced dynamic brain and cardiovascular effects are yet missing. Here, we tested various auditory stimulation approaches in a windowed, 10 s ON (stimulations) followed by 10 s OFF (no stimulations), within-night stimulation design and compared them to a SHAM control condition. We report the results of three studies and a total of 51 included nights and found a large and global increase in slow-wave activity (SWA) in the stimulation window compared to SHAM. Furthermore, slow-wave dynamics were most pronouncedly increased at the start of the stimulation and declined across the stimulation window. Beyond the changes in brain oscillations, we observed, for some conditions, a significant increase in the mean interval between two heartbeats within a stimulation window, indicating a slowing of the heart rate, and increased heart rate variability derived parasympathetic activity. Those cardiovascular changes were positively correlated with the change in SWA, and thus, our findings provide insight into the potential of auditory slow wave enhancement to modulate cardiovascular restorative conditions during sleep. However, future studies need to investigate whether the potentially increased restorative capacity through slow-wave enhancements translates into a more rested cardiovascular system on a subsequent day.

Targeted memory reactivation during sleep influences social bias as a function of slow‐oscillation phase and delta power

“…Perhaps this rhythm entrained EEG oscillations in some participants, influencing slow-oscillation phase and delta power changes. Indeed, a recent study suggests that openloop auditory stimulation can induce slow-oscillation amplitude changes (Huwiler et al, 2022). Batterink et al (2016) first reported that TMR benefits were predicted by slow-oscillation phase at the time of cueing: cues played during one particular interval of the slow-wave cycle (180-270°) led to less forgetting of cued items than did cues played during other phases.…”

“…Perhaps this rhythm entrained EEG oscillations in some participants, influencing slow‐oscillation phase and delta power changes. Indeed, a recent study suggests that open‐loop auditory stimulation can induce slow‐oscillation amplitude changes (Huwiler et al, 2022).…”

Alpha closed-loop auditory stimulation modulates waking alpha oscillations and sleep onset dynamics in a phase-dependent manner in humans

“…Although a recent study using TACS to target alpha oscillations reported a transient suppression of alpha power independent of the phase at which stimulation was applied 27 . Meanwhile, studies employing auditory stimulation in the same closed-loop manner have demonstrated that administering sounds at different phases of sleep's hallmark slow oscillation leads to different effects, such that sounds applied at the peak of slow oscillations increase its amplitude [28][29][30][31][32] (but see 33 ). In comparison to electrical stimulation, auditory stimulation offers several advantages, as it is inexpensive, easy to apply, has minimal side effects, and it does not cause artifacts on the electrophysiological (EEG) signal, thus permitting straightforward continuous monitoring of brain activity.…”

“…Closed-loop sensory stimulation has the potential to overcome this limitation, since sensory stimuli do not create artefacts in the EEG (allowing repeated neurophysiological interrogation), with the additional advantage of utilising safe, easy to apply and affordable technology. This approach has been used in sleep studies in which sounds are commonly phase-locked to the slow-oscillations (0.5-4Hz) of sleep [27][28][29][30][31][32][33].…”

“…Some of these studies have found a phase-dependent effect of stimuli and, in this case, their primary outcome is often neurophysiological. Thus, sounds boost or diminish slowoscillations on a phase-dependent basis [27][28][29][30][31][32][33], although this remains contentious [29].…”