Individual neurophysiological signatures of spontaneous rhythm processing

When sensory input conveys rhythmic regularity, we are able to form predictions about the timing of upcoming events. Although rhythm processing capacities can differ considerably between individuals, these differences are often obscured by subject- and trial-level data averaging procedures in M/EEG research. Here, instead, we systematically assessed the neurophysiological variability exhibited by individuals listening to isochronous equitone sequences interspersed with unexpected deviant tones. First, we focused on rhythm tracking and tested the phase-relationship between neural activity in the delta-band and pre-tone onsets. We observed clear between- and within-subject variability, confirming that individuals employ variable, flexible, but consistent rhythm tracking at the single-trial level. Next, we modelled single-trial time-locked neural responses in the beta-band to investigate individual tendencies to employ binary or triplet grouping ('tic-toc effect'). Beta-band activity showed binary (strong-weak), triplet (strong-weak-weak) and mixed accentuation patterns, resembling the superimposition of a beat. Thus, we identified individual preferences for grouping patterns and tendencies to switch between binary, triplet, or combined patterns over trials. Notably, we demonstrated that the processing of standard and deviant tones was modulated by the employed grouping. This approach to neurophysiological profiling offers a sensitive strategy to identify individual and dynamically evolving neural signatures of rhythm and beat processing. We suggest that the observed neurophysiological variability reflects flexible windows of opportunity for evaluating and adapting to (un)predictable environmental rhythms. ### Competing Interest Statement The authors have declared no competing interest.