Intrinsic Rhythmicity Predicts Synchronization-Continuation Entrainment Performance

Abstract

Rhythmic entrainment-defined as a stable temporal relationship between external periodic signals and endogenous rhythmic processes-allows individuals to coordinate with environmental rhythms. However, the impact of inter-individual differences on entrainment processes as a function of the tempo of external periodic signals remain poorly understood. To better understand the effects of endogenous differences and varying tempos on rhythmic entrainment, 20 young healthy adults participated in a spontaneous motor tempo (SMT) task and synchronization-continuation tasks at three experimental tempos (50, 70, and 128 bpm; 1200, 857, and 469 ms inter onset interval (IOI)). We hypothesized that SMT task performance and tempo would influence externally paced synchronization-continuation task behavior. Indeed, intrinsic rhythmicity assessed through the SMT task predicted performance in the externally paced task, allowing us to characterize differences in entrainment behavior between participants with low and high endogenous rhythmicity. High rhythmicity individuals, defined by better SMT performance, deviated from externally paced pulses sooner than individuals with low rhythmicity, who were able to maintain externally paced pulses for longer. The magnitude of these behavioral differences depended on the experimental tempo of the synchronization-continuation task. Our results indicate that differences in intrinsic rhythmicity vary between individuals and relate to tempo-dependent entrainment performance.

Figure 1

Phase Locking Value (PLV) analysis. (A–C) Scatterplots and spearman correlations for PLV from the SMT task against PLV in each of the three paced conditions (50, 70, and 128 bpm; 1200, 857, and 469 ms IOI) from the synchronization-continuation task. (D) After splitting participants into a high rhythmicity and a low rhythmicity group based off of SMT PLV, significant differences were found between high and low rhythmicity groups in the 50 bpm (1200 ms IOI) and 128 bpm (469 ms IOI) conditions.

Figure 2

Inter Onset Interval (IOI) analysis. (A) One example of the IOI time course plots generated at each experimental tempo (50, 70, and 128 bpm; 1200, 857, and 469 ms IOI) for each participant. Here, the 50 bpm (1200 ms IOI) IOI time course data for one participant is plotted and fitted with a linear regression. Slopes were extracted from linear regressions of the data of each participant in each tempo conditions. The red dashed line indicates the IOI of the externally paced prompt—1200 ms. (B) Normalized IOI values were split into early and late groups, depending on whether they fell in the first or last 15-seconds of each trial. This allowed for a comparison of the synchronization vs. continuation entrainment phases of the synchronization-continuation task. A significant interaction between tempo and group demonstrates that faster tempos cause more variability during continuation entrainment. (C) The absolute values of extracted normalized IOI slopes were used to compare how high and low rhythmicity groups deviated from the paced pulse during the transition to continuation entrainment. A main effect for tempo demonstrated that slower tempos lead participants to deviate more from the original prompt frequency.

Figure 3

Drift Value analysis. (A) The 128 bpm (469 ms IOI) drift value data for one participant plotted along with the condensed mean drift time course and sigmoidal function fitting of that time course. (B) t0 coefficients were extracted from the sigmoidal fits and represented the midpoint of the function. These were compared across high and low rhythmicity groups and tempo conditions (50, 70, and 128 bpm; 1200, 857, and 469 ms IOI), revealing a main effect for group that was significant in the 50 bpm (1200 ms IOI) condition. (C) Tau coefficients were extracted from the sigmoidal fits and represented the time-constant (inverse of the maximum slope) of the function. No significant findings were found for tau. (D–F) Plotted time courses for the averaged mean drift time courses for all individuals in the high and low rhythmicity groups at each experimental tempo (50, 70, and 128 bpm; 1200, 857, and 469 ms IOI). See Supplementary Fig. 2 for all participant mean drift time courses plotted together and all participant sigmoidal function fits.

Figure 4

Study and task design. (A) Each participant participated in an SMT task block and three synchronization-continuation task blocks that were all preceded by and interspersed with 5-minute resting periods. (B) The SMT task block consisted of 10 identical SMT task trials that were presented in succession. (C) The synchronization-continuation task block consisted of 21 trials—7 at each of the three experimental tempos (50, 70, and 128 bpm; 1200, 857, and 469 ms IOI)—presented in a random order.