Effect of Rocking Movements on Afternoon Sleep

Abstract

Study Objectives: Gentle rocking movements provided by a moving bed have been proposed as a promising non-pharmacological way to promote sleep. In rodents the sleep promoting effect of rocking movements depended on the peak acceleration (named "stimulation intensity") perceived by the vestibular system. We set out to verify previous reports on the sleep promoting effect of rocking movements and to investigate the importance of stimulation intensity in this process. Methods: Side-to-side rocking movements along a pendulum trajectory with different peak accelerations (control: 0 m/s 2 , low intensity: 0.15 m/s 2 , medium intensity: 0.25 m/s 2 , high intensity: 0.35 m/s 2) were provided for 45 min during an afternoon nap opportunity. Participants were assigned to a low intensity group (n = 10) experiencing control, low and medium intensity stimulation or a high intensity group (n = 12) experiencing control, medium and high intensity stimulation. Sleep and sleep-related memory performance were assessed using polysomnography and a word-pair memory task, respectively. Results: Participants transitioned faster into deep sleep under the influence of medium intensity rocking as was evident by a faster buildup of delta power compared to the control condition (n = 22). The faster buildup did not affect sleep architecture, since e.g., the proportion of the nap spent in deep sleep or latencies did not change. Previously reported effects like a shorter latency to stage N2 and a higher density of sleep spindles were not observed. Sleep quality during control naps of the low intensity group was worse than in the high intensity group. In the low intensity group, we also observed a significant increase in delta power throughout the nap, as well as a higher density of slow oscillations both under the influence of low and medium intensity vestibular stimulation. No such effects were observed in the high intensity group. Conclusion: Rocking movements may promote nap sleep in young adults. Due to a difference in sleep quality during control naps between the low and high intensity group no conclusion regarding the influence of stimulation intensity were possible. Thus, optimal stimulation settings in humans need further investigation.

Gentle rocking movements during sleep in the elderly

“…Vestibular stimulation using subjectively preferred stimulation direction and intensity did not improve sleep in our sample of elderly participants. Unlike studies in younger adults, we did not observe a facilitation of sleep onset, more deep sleep or an increase in the number or density of sleep spindles (Omlin et al, 2018;Shibagaki et al, 2017;Woodward et al, 1990). On the contrary, we observed reduced delta power, suggesting a reduced sleep depth under the influence of rocking movements.…”

“…When a rotational component is added to the stimulation, it is clear to the body that the stimulation is tilt and, thus, the sensory mismatch is solved. This could explain the difference between our findings and previous reports of a promotion of sleep through rocking movements (Bayer et al, 2011;Perrault et al, 2019;Shibagaki et al, 2017). Twelve out of 18 subjects in the study by Omlin and colleagues selected movements with a rotational component, and this could explain why also in this study only a weak effect of vestibular stimulation on sleep was observed (Omlin et al, 2018).…”

“…Thus, it might be that the linear peak acceleration of 0.15 m/s 2 used in this study, although above the average perception threshold in adults aged 18-40 years (0.064 m/s 2 ), was too low (i.e., too close to the perception threshold) to promote sleep in adults over 60 years of age. Indeed, we are at the lower limit of the intensities (accelerations) that have been tested in other studies (Bayer et al, 2011;Omlin et al, 2018;Perrault et al, 2019;Shibagaki et al, 2017;Woodward et al, 1990). In a recent study on the effect of rocking movements with different stimulation intensities (0.15-0.35 m/s 2 ) on nap sleep there was no indication of an intensity-dependent effect.…”

“…The gentle movements provided in studies investigating the effect of rocking movements on sleep (Bayer et al, 2011;Omlin et al, 2018;Perrault et al, 2019;Shibagaki et al, 2017;Woodward et al, 1990) are too subtle to induce motion sickness but might evoke tiredness through this mismatch. When a rotational component is added to the stimulation, it is clear to the body that the stimulation is tilt and, thus, the sensory mismatch is solved.…”

“…Recently, vestibular stimulation in the form of gentle rocking movements has been proposed as a promising therapeutic modality. Sleep-promoting effects reported in young adults include facilitation of wake-to-sleep transition (Bayer et al, 2011;Perrault et al, 2019;Woodward, Tauber, Spielmann, & Thorpy, 1990) and more deep sleep (Perrault et al, 2019;Shibagaki, Ashida, Morita, Ikeura, & Yokoyama, 2017).…”