Inter- and intra-individual differences in temporal modulation patterns of the β-band sensorimotor rhythm and its relationship to corticomuscular coherence during intermittent voluntary contraction

The β-band sensorimotor rhythm (SMR), recorded using electroencephalography, generally desynchronizes from motor preparation and subsequently synchronizes with electromyogram signals during voluntary contraction, thus forming corticomuscular coherence (CMC). However, it remains unclear how the temporal modulation of β-band SMR varies among individuals, potentially leading to individual differences in CMC. It is also unclear how the nervous system modulates β-band SMR to meet varying task demands within individuals. Here, we explored how temporal modulation patterns of β-band SMR affect CMC from two perspectives: inter-individual differences (Experiment 1), and intra-individual variability depending on task demands (Experiment 2). In Experiment 1, participants repeated a steady-force maintenance task. The degree of β-band SMR modulation (i.e., rebound from desynchronization to synchronization) during contractions varied greatly among individuals and was positively correlated with CMC magnitude. This suggests that even under steady-force maintenance, the motor control strategy used while regulating β-band SMR varies greatly among individuals. In Experiment 2, participants who showed significant CMC in Experiment 1 performed four tasks with varying target trajectories. Even within individuals, the degree of β-band SMR modulation was reduced in parallel with the CMC magnitude as more difficult force adjustment was required. This finding suggests that, when confronted with more challenging task demands, our nervous system reduces the oscillation of SMR and desynchronizes its coupling with muscles. Overall, the way in which our nervous system regulates β-band SMR is assumed to represent a strategy for flexible adaptation to diverse motor environments.