Increase deep sleep quality8/31/2023 ![]() ![]() ![]() 3, 4, 6, 14, 19 The extent to which environmental or noise pollution effects might differ from those of low-frequency enhancing audio, either momentarily or across a whole night, is unclear. 18 Pink noise, timed to coincide with up-states of SO activity, is the only auditory stimulation reported to enhance SOs. The ability of a sound to produce sleep disruption varies by pressure level (ie, loudness), threat valence, and sleep stage during presentation. However, microarousals (as defined in part by their brevity) do not always lead to neurocortical waking activity of ≥15 sec, and therefore may not lead to increases in wake time even if frequent. Sleep architecture (the distribution of sleep stages and wakefulness) appears largely unaffected by auditory intervention, 10– 14 excepting one study 15 that improved sleep efficiency. 8 Phase-locked auditory stimulation appears to preserve microarousal frequency, 9 but impact on sleep continuity remains unreported for auditory open-loop approaches where sleep disruption is more likely. Sleep fragmentation reduces behavioral, physiologic, and perceived restoration by sleep. 7 The viability of open-loop stimulation in the field is dependent upon not only the magnitude of the effect, however, but also of open-loop’s tolerability and ability to preserve sleep quality (eg, to not induce awakenings). 6 With such open-loop constraints to endogenous deep sleep, and phase-locked constraints to endogenous SO activity, it remains unclear how auditory-induced low-frequency enhancement might improve sleep architecture on the whole where other non-auditory stimulus modalities have been successful. 6 This N3 and transient power spectral increase is accomplished when open-loop stimulation is constrained to the early sleep period. 3, 4 Open-loop stimulation that is supervised and limited to N3 sleep fails to improve word pair memory, 6 which was observed in phase-locked studies, 4, 5 but open-loop stimulation can elicit a modest increase in N3 sleep proportion 4, 6 in addition to both SO and delta enhancement. Open-loop stimulation literature is sparse partly because auditory stimulation synchronous with the SO up-state is the more effective elicitor of momentary SO power, 4 despite the marginal or suppressive effect of phase-locked stimulation on broader-spectrum delta activity that occurs during deep sleep. The non-phase-locked, open-loop approach to auditory stimulation has a translational advantage in ultimate ecological implementation, because of phase locking’s EEG requirement. 3– 6 Whether low-frequency activity is ontogenically or neurochemically similar to that in endogenous non-rapid eye movement (NREM) stage 3 (N3) sleep is not yet elucidated, but evoked SO waves demonstrate similar electrical field topography as those produced endogenously. 1, 2 Auditory stimulation administered both in phase with endogenous delta activity (“phase locking” with EEG detection) and without phase locking (“open-loop”) enhances slow oscillatory (SO 0.5–1 Hz) power, while the phase-locked effect on broader delta-frequency power (0.5–4 Hz) is equivocal. Preserving sleep continuity should be a primary consideration if auditory stimulation is utilized to enhance slow-wave activity and deepen sleep.Īuditory stimulation during sleep can increase the power of delta-frequency electroencephalographic (EEG) activity by either eliciting K-complexes or increasing amplitude in the low-frequency spectral range. The current work indicates the potential utility of auditory stimulation presented below the arousal threshold to increase restorative deep sleep without the need for precise timing of sounds to brain waves. After the Disruptive night, next-day attention performance was impaired (versus Sham) despite preserved sleep duration and momentary increases in slow-wave activity. Alerting sounds, such as an IV alarm, were momentarily effective in increasing slow-wave activity, but the all-night proportion of deep sleep (versus a Sham control night) increased only on the Enhancing night. Both pink noise (less high-frequency content than white noise) on an “Enhancing” night and sounds without standard pink noise features administered on a “Disruptive” night produced increases in momentary slow-wave brain activity, characteristic of deep sleep. This work demonstrates the potential utility of auditory stimulation, not precisely timed to brain wave activity, to increase deep sleep among mid-life adults. Deep sleep, considered the most restorative stage of sleep, decreases with advancing age. ![]()
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