The Effect of a Slowly Rocking Bed on Sleep

Abstract

Rocking movements appear to affect human sleep. Recent research suggested a facilitated transition from wake to sleep and a boosting of slow oscillations and sleep spindles due to lateral rocking movements during an afternoon nap. This study aimed at investigating the effect of vestibular stimulation on sleep onset, nocturnal sleep and its potential to increase sleep spindles and slow waves, which could influence memory performance. Polysomnography was recorded in 18 males (age: 20–28 years) during three nights: movement until sleep onset (C1), movement for 2 hours (C2), and one baseline (B) without motion. Sleep dependent changes in memory performance were assessed with a word-pair learning task. Although subjects preferred nights with vestibular stimulation, a facilitated sleep onset or a boost in slow oscillations was not observed. N2 sleep and the total number of sleep spindles increased during the 2 h with vestibular stimulation (C2) but not over the entire night. Memory performance increased over night but did not differ between conditions. The lack of an effect might be due to the already high sleep efficiency (96%) and sleep quality of our subjects during baseline. Nocturnal sleep in good sleepers might not benefit from the potential facilitating effects of vestibular stimulation.

Whole-Night Continuous Rocking Entrains Spontaneous Neural Oscillations with Benefits for Sleep and Memory

“…Because both somatosensory and vestibular systems send direct inputs to the thalamus [1,45,46], their rocking-induced rhythmic stimulation might entrain SOs and spindles within Table S2. thalamocortical circuits. Hence, this mechanism would in turn favor spindles' function in protecting sleep and explain why we also observed changes in the architecture of sleep (increase in N3 duration, decrease in arousals), unlike other studies in which pulsed sensory stimulations were used [8,12,13] or rocking was used only during the first 2 h of sleep [16]. Importantly, we demonstrated that the rocking-induced spindles had unaltered phase coupling with the SO.…”

“…A shortening of sleep latency caused by sensory stimulations was previously reported in the pioneering study by Pompeiano and Swett (1962), who applied regular low-intensity cutaneous electric stimulations in cats [22], and by more recent studies in humans using electrical, olfactory, or rocking stimulations [7,16,[23][24][25]. Here, beyond a mere facilitation of sleep initiation with an overall reduction in sleep latency to N2 and a tendency to enter faster into N3, we also found that rocking profoundly modified the architecture of sleep, with an increase in N3 duration and a decrease in N2 (and N1) duration, while REM sleep remained unaffected.…”

“…Using a 0.42-Hz rocking bed, Woodward and collaborators (1990) did not report any changes in N2 or N3 durations, but they observed a reduced sleep latency under the rocking condition [24]. Recently, Omlin and colleagues (2018) investigated the effect of a rocking stimulation when applied until sleep onset or during the first 2 h of sleep and found no change in sleep latency, but they found an increase in N2 duration under 2 h of the rocking condition [16]. In this particular study, the frequency (0.16 or 0.24 Hz) and the direction of motion applied to the bed (5 possibilities: 3 linear translations and 2 swing rotations) were chosen based on each participant's subjective preference, thus resulting in between 2 and 5 participants per specific motion characteristics.…”

“…The EEG spectrum power average (30 s of time resolution with artefact excluded) was calculated with a 0.2 Hz resolution, by applying a Fast Fourier Transformation (FFT; 50% overlapping, 5 s windows, Hanning filter) using the midline frontal (Fz) and parietal (Pz) derivations. Mean power was calculated for each 0.2 bins between 0.4 and 30 Hz and for the following frequency bands: SOs (0.4-1 Hz), delta (1-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), sigma (11.5-15 Hz), slow and fast spindle power ranges (8.5-12 Hz on Fz and 12-15 Hz on Pz, respectively), low beta (15)(16)(17)(18)(19) and high beta (19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). Following the procedure of Ray and colleagues [70], spindles were detected automatically using the PRANA software.…”

“…Such entrainment of ongoing brain oscillations by an external drive is thought to involve a mechanism of neural phase reset reflecting the reorganization of the ongoing brain oscillations, specifically when applied in pulsed stimulation [8][9][10][11][12][13]15]. In contrast, continuous cyclic stimulation [7,16] might also entrain endogenous brain rhythms by synchronizing to the stream of external events without imposing a phase-reset mechanism [15]. The modality of application of a sensory stimulus can alter its effect on sleep-wake architecture and highlights the importance of the methodology used [17].…”