Slow wave sleep (SWS) is characterized by the predominance of delta waves and slow oscillations, reflecting the synchronized activity of large cortical neuronal populations. Amongst other functions, SWS plays a crucial role in the restorative capacity of sleep. Rhythmic Acoustic Stimulation (RAS) during SWS has been shown a cost-effective method to enhance slow wave activity. Slow wave activity can be expressed in a region-specific manner as a function of previous waking activity. However, it is unclear whether slow waves can be enhanced in a region-specific manner using RAS. We investigated the effects of unilaterally presented rhythmic acoustic sound patterns on sleep EEG oscillations. Thirty-five participants received during SWS 12-seconds long rhythmic bursts of pink noise (at a rate of 1 Hz) that alternated with non-stimulated, silent periods, unilaterally delivered into one of the ears of the participants. As expected, RAS enhanced delta power, especially in its low frequency components between 0.75 and 2.25 Hz. However, increased slow oscillatory activity was apparent in both hemispheres regardless of the side of the stimulation. The most robust increases in slow oscillatory activity appeared during the first 3-4 seconds of the stimulation period. Furthermore, a short-lasting increase in theta and sigma power was evidenced immediately after the first pulse of the stimulation sequences. Our findings indicate that lateralized RAS has a strong potential to globally enhance slow waves during daytime naps. The lack of localized effects suggests that slow waves are triggered by the ascending reticular system and not directly by specific auditory pathways.

Aim: Although people living with Down syndrome have high demand for dental care treatment, dissolving dental fear makes the choice of proper methods extremely difficult. The aim of the study was finding a new method for solving this problem. Materials and methods:In the present study, a 10-minute-long photo-acoustic stimulation with rhythmic sounds or relaxation music was used for tranquilizing the patients before a dental examination. Thirty volunteers living with Down syndrome participated in the study. They were divided into three groups (rhythmic sound, relaxation music, and control groups). A piece of Johan Sebastian Bach (Bach Cello Suite No. 1 in G major BWvi007) was applied as a relaxing music. Spielberger State-Trait Anxiety Inventory (STAI) Child version, Dental Anxiety Scale (DAS), and Dental Anxiety Question (DAQ) were used for measuring the anxiety level of the participants. Results:The results confirm the first hypothesis, namely that photo-acoustic stimulation with rhythmic sounds or relaxation music is suitable for decreasing the level of fear of dental patients living with Down syndrome. The other hypothesis that the anxiety-suppressing effect of light stimulation with classical music would be larger than that of light stimulation with rhythmic sounds was not proven statistically. Conclusion:The results suggest that application of photoacoustic method by using either relaxing music or rhythmic sounds is able to reduce dental fear of patients although some contraindications should be respected (e.g., the presence of epilepsy). Clinical significance:The importance of photo-acoustic stimulation in dental fear reduction is underestimated and deserves higher attention, especially in case of people living with Down syndrome.

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