Spontaneous group synchronization of movements and respiratory rhythms

Abstract

We tested whether pre-assigned arm movements performed in a group setting spontaneously synchronized and whether synchronization extended to heart and respiratory rhythms. We monitored arm movements, respiration and electrocardiogram at rest and during spontaneous, music and metronome-associated arm-swinging. No directions were given on whether or how the arm swinging were to be synchronized between participants or with the external cues. Synchronization within 3 groups of 10 participants studied collectively was compared with pseudo-synchronization of 3 groups of 10 participants that underwent an identical protocol but in an individual setting. Motor synchronization was found to be higher in the collective groups than in the individuals for the metronome-associated condition. On a repetition of the protocol on the following day, motor synchronization in the collective groups extended to the spontaneous, un-cued condition. Breathing was also more synchronized in the collective groups than in the individuals, particularly at rest and in the music-associated condition. Group synchronization occurs without explicit instructions, and involves both movements and respiratory control rhythms.

Figure 1. Portable experimental device.

The device acquired electrocardiogram, respiratory excursion and arm movement, at the frequency of 400 Hz/channel. The data were acquired simultaneously from the ten participants and synchronized through a built-in XBEE radio module and saved on SD card.

Figure 2. Collective measurement group setup.

Left Panel: position of the participants during the study. Right panel: participants of the study during the protocol. The individuals in this manuscript gave written informed consent, as outlined in the PLOS consent form, to participate in the study and to publish their case details. The Ethics committee of the University of Pavia, Italy approved the study protocol.

Figure 3. Generalized Partial Directed Coherence (GPDC).

Example of multivariate (GPDC) coherence spectra matrix, related to the abdominal respiration signal in the music-associated condition, and in the 10 subjects (S1–S10) of the first collective measurement group on the first day. In each spectrum the abscissa reports the frequency in Hz, and the ordinate reports the coherence, from 0 to 1. Each subject is compared with all the other subjects and with him/herself in the diagonal. Note that the coherence in the diagonal is lower than 1, as each subject is compared with himself, but in the context of a multivariate model that takes into account also the remaining subjects.

Figure 4. Coherence analysis – Arm movements.

The histograms show the degree of synchronization between participants of the arm movement (accelerometer signal), during the five phases of the study: initial resting baseline, spontaneous movement, music-associated movement, metronome-associated movement and final resting baseline. Participants from the individual measurement group are shown in gray; participants from the collective measurement group are shown in colours, with different colours representing the repetition of the protocol over the course of two days. Top panel. Results of the coherence in the high frequency band (HF: 0.15–0.4 Hz). Movements were more synchronized in the collective measurement groups for the metronome-associated condition. The greater synchronization of the fluctuations of the accelerometer signal in the resting baseline for the individual measurement groups rules out the possibility that the superior synchronization of the collective in the metronome-associated condition was due to artifacts or differences in the baseline level of the accelerometer signal. Bottom panel. Results of the coherence in the very high frequency band (VHF: 0.4–2 Hz). Movements were overall more synchronized in the collective measurement groups than in the individual measurement groups. On the repetition of the protocol, the peak of synchronization previously observed in the metronome-associated condition decreases, while an increase of collective synchronization is observed for the spontaneous, un-cued movements.

Figure 5. Coherence analysis – Respiration.

The histograms show the degree of synchronization between participants for the abdominal (top panel) and thoracic (bottom panel) respiratory signals, in the very high frequency band (VHF: 0.4–2 Hz), during the five phases of the study (see Figure 4 for details). Participants in the collective measurement group show greater synchronization of respiration than participants in the individual measurement group. This is especially pronounced in the initial resting baseline and in the music-associated condition.